Awl --

Recently, on one of these How They Do It ditties, they featured but more
Dubai profligacy, this time indoor skiing in the middle of the effing
desert.

The key to the insulation, they explained, was a huge air gap, asserting
that air -- caveat: trapped non-moving air -- was among the best
insulators.

First, is this true? Before I insulated my roof, that air would become
blisteringly hot, and it didn't seem to be moving much. That attic seemed
like a pretty good air gap to me, and it didn't seem to be doing much
insulating.

Second, I seem to remember one strategy where push/pull fans were used with
air gaps in a roof-type situation, to keep air flowing, to reduce the
heating transfer, like what accumulated in my attic -- ie, the exact
opposite of static air.

Now mebbe air behaves differently in conduction vs. *radiant* heat from
roof-type situations that is making the attic so hot, not hot air itself --
if the two can be distinguished wrt air.

iirc, the Dubai ditty used reflection, insulation, AND that big air gap.....

But I've read about this insulating property of air before, so I'm wondering
how it might be employed in a house.
It would seem that if air itself was so good, solid insulation wouldn't be
so high a priority

I wonder what mooslims think about Dubai.....
--
EA

On Wed, 27 Jul 2011 10:20:23 -0400, "Existential Angst"
wrote:

It would seem that if air itself was so good, solid insulation wouldn't be
so high a priority

The key here is convection. Even though the air is enclosed in an
airtight room, the air will circulate inside the room so that the
temperature becomes fairly evenly distributed. The point of insulation
material is to prevent this convection, so that the air stays still.

The insulation material must also have low heat conduction, which is
why it is made from rock or glass, and not copper or aluminium.

Some scuba divers replace the air in their drysuit with argon to stay
a little bit warmer. It only makes a small difference, though.
--
RoRo

On Jul 27, 10:20*am, "Existential Angst" wrote:
Awl --

Recently, on one of these How They Do It ditties, they featured but more
Dubai profligacy, this time indoor skiing in the middle of the effing
desert.

The key to the insulation, they explained, was a huge air gap, asserting
that air -- caveat: *trapped non-moving air -- was among the best
insulators.

First, is this true? *Before I insulated my roof, that air would become
blisteringly hot, and it didn't seem to be moving much. *That attic seemed
like a pretty good air gap to me, and it didn't seem to be doing much
insulating.

Second, I seem to remember one strategy where push/pull fans were used with
air gaps in a roof-type situation, to keep air flowing, to reduce the
heating transfer, like what accumulated in my attic -- ie, the exact
opposite of static air.

Now mebbe air behaves differently in conduction vs. *radiant* heat from
roof-type situations that is making the attic so hot, not hot air itself -- *
if the two can be distinguished wrt air.

iirc, the Dubai ditty used reflection, insulation, AND that big air gap......

But I've read about this insulating property of air before, so I'm wondering
how it might be employed in a house.
It would seem that if air itself was so good, solid insulation wouldn't be
so high a priority

I wonder what mooslims think about Dubai.....
--
EA

You've got a bunch of apples and oranges mixed up in your fruit salad.
In your attic, you have a roof which is being heated by the sun. Then
you have convection, which mixes up the attic air and brings it in
contact with the lower floor's ceiling. The object of insulation
material is to keep the air still, to (virtually) eliminate the
convection.

a properly vented attic space should have a considerably lower
temperature. Air is drawn into the soffit vents and expelled through
the ridge vent. Even better is a powered ventilator or, the push-pull
fans you mentioned. In the ventilated space, the sun-heated air is
replaced with cooler ambient outside air. This has nothing to do with
the insulation value of the air, just its temperature.

Besides the house cooling issues, it is generally a good thing for the
logevity of the roofing materials to keep the inside attic temperature
as close as possible to the outside temperature.

A reflective roof would make a huge difference. I don't understand the
fascination with black (or othr dark color) roofing shingles.

On Jul 27, 11:25*am, rangerssuck wrote:
On Jul 27, 10:20*am, "Existential Angst" wrote:





Awl --

Recently, on one of these How They Do It ditties, they featured but more
Dubai profligacy, this time indoor skiing in the middle of the effing
desert.

The key to the insulation, they explained, was a huge air gap, asserting
that air -- caveat: *trapped non-moving air -- was among the best
insulators.

First, is this true? *Before I insulated my roof, that air would become
blisteringly hot, and it didn't seem to be moving much. *That attic seemed
like a pretty good air gap to me, and it didn't seem to be doing much
insulating.

Second, I seem to remember one strategy where push/pull fans were used with
air gaps in a roof-type situation, to keep air flowing, to reduce the
heating transfer, like what accumulated in my attic -- ie, the exact
opposite of static air.

Now mebbe air behaves differently in conduction vs. *radiant* heat from
roof-type situations that is making the attic so hot, not hot air itself -- *
if the two can be distinguished wrt air.

iirc, the Dubai ditty used reflection, insulation, AND that big air gap......

But I've read about this insulating property of air before, so I'm wondering
how it might be employed in a house.
It would seem that if air itself was so good, solid insulation wouldn't be
so high a priority

I wonder what mooslims think about Dubai.....
--
EA

You've got a bunch of apples and oranges mixed up in your fruit salad.
In your attic, you have a roof which is being heated by the sun. Then
you have convection, which mixes up the attic air and brings it in
contact with the lower floor's ceiling. The object of insulation
material is to keep the air still, to (virtually) eliminate the
convection.

a properly vented attic space should have a considerably lower
temperature. Air is drawn into the soffit vents and expelled through
the ridge vent. Even better is a powered ventilator or, the push-pull
fans you mentioned. In the ventilated space, the sun-heated air is
replaced with cooler ambient outside air. This has nothing to do with
the insulation value of the air, just its temperature.

Besides the house cooling issues, it is generally a good thing for the
logevity of the roofing materials to keep the inside attic temperature
as close as possible to the outside temperature.

A reflective roof would make a huge difference. I don't understand the
fascination with black (or othr dark color) roofing shingles.- Hide quoted text -

- Show quoted text -

Now, having said all that, I have a related question:

My attic floor is insulated, but rather poorly. Adding more insulation
in the attic would not be easy. I am getting ready to repair the
ceilings in two bedrooms. The plaster is badly cracked and there are
definitely some broken keys (plaster / wood lath). The standard
parctice is to install furring strips and sheetrock over the plaster.
What I'm thinking about is adding a couple of inches of ridgid foam
insulation between the plaster and sheetrock.

I'd use screws and plaster washers to secure the existing ceiling to
the joists. Then use screws with fender washers to secure the
insulation, and then screw the sheetrock through the wholew mess to
the joists with, say, 3 1/2" sheetrock screws. I CAN afford to give up
a couple of inches of ceiling height.

Is this plan at all sane?

"rangerssuck" wrote in message
...

A reflective roof would make a huge difference. I don't understand the
fascination with black (or othr dark color) roofing shingles.

Some people don't live in a cooling-dominated climate.

--

On Jul 27, 11:06*am, Robert Roland wrote:
On Wed, 27 Jul 2011 10:20:23 -0400, "Existential Angst"

wrote:
It would seem that if air itself was so good, solid insulation wouldn't be
so high a priority

The key here is convection. Even though the air is enclosed in an
airtight room, the air will circulate inside the room so that the
temperature becomes fairly evenly distributed. The point of insulation
material is to prevent this convection, so that the air stays still.

The insulation material must also have low heat conduction, which is
why it is made from rock or glass, and not copper or aluminium.

Some scuba divers replace the air in their drysuit with argon to stay
a little bit warmer. It only makes a small difference, though.
--
RoRo

http://en.wikipedia.org/wiki/Insulated_glazing
"Typically, most sealed units achieve maximum insulating values using
a gas space of between 5/8 to 3/4” (16–19 mm) when measured at the
centre of the IGU."

AFAIK thicker air spaces permit heat transfer by convection.

jsw

On Jul 27, 9:33*am, rangerssuck wrote:
On Jul 27, 11:25*am, rangerssuck wrote:





On Jul 27, 10:20*am, "Existential Angst" wrote:

Awl --

Recently, on one of these How They Do It ditties, they featured but more
Dubai profligacy, this time indoor skiing in the middle of the effing
desert.

The key to the insulation, they explained, was a huge air gap, asserting
that air -- caveat: *trapped non-moving air -- was among the best
insulators.

First, is this true? *Before I insulated my roof, that air would become
blisteringly hot, and it didn't seem to be moving much. *That attic seemed
like a pretty good air gap to me, and it didn't seem to be doing much
insulating.

Second, I seem to remember one strategy where push/pull fans were used with
air gaps in a roof-type situation, to keep air flowing, to reduce the
heating transfer, like what accumulated in my attic -- ie, the exact
opposite of static air.

Now mebbe air behaves differently in conduction vs. *radiant* heat from
roof-type situations that is making the attic so hot, not hot air itself -- *
if the two can be distinguished wrt air.

iirc, the Dubai ditty used reflection, insulation, AND that big air gap.....

But I've read about this insulating property of air before, so I'm wondering
how it might be employed in a house.
It would seem that if air itself was so good, solid insulation wouldn't be
so high a priority

I wonder what mooslims think about Dubai.....
--
EA

You've got a bunch of apples and oranges mixed up in your fruit salad.
In your attic, you have a roof which is being heated by the sun. Then
you have convection, which mixes up the attic air and brings it in
contact with the lower floor's ceiling. The object of insulation
material is to keep the air still, to (virtually) eliminate the
convection.

a properly vented attic space should have a considerably lower
temperature. Air is drawn into the soffit vents and expelled through
the ridge vent. Even better is a powered ventilator or, the push-pull
fans you mentioned. In the ventilated space, the sun-heated air is
replaced with cooler ambient outside air. This has nothing to do with
the insulation value of the air, just its temperature.

Besides the house cooling issues, it is generally a good thing for the
logevity of the roofing materials to keep the inside attic temperature
as close as possible to the outside temperature.

A reflective roof would make a huge difference. I don't understand the
fascination with black (or othr dark color) roofing shingles.- Hide quoted text -

- Show quoted text -

Now, having said all that, I have a related question:

My attic floor is insulated, but rather poorly. Adding more insulation
in the attic would not be easy. I am getting ready to repair the
ceilings in two bedrooms. The plaster is badly cracked and there are
definitely some broken keys (plaster / wood lath). The standard
parctice is to install furring strips and sheetrock over the plaster.
What I'm thinking about is adding a couple of inches of ridgid foam
insulation between the plaster and sheetrock.

I'd use screws and plaster washers to secure the existing ceiling to
the joists. Then use screws with fender washers to secure the
insulation, and then screw the sheetrock through the wholew mess to
the joists with, say, 3 1/2" sheetrock screws. I CAN afford to give up
a couple of inches of ceiling height.

Is this plan at all sane?- Hide quoted text -

- Show quoted text -

Yup, my dad did the same at our old house. We had high ceilings,
though, newer crackerbox construction wouldn't have enough room. The
way we did it was to put up some 2x furring strips on edge, then fill
in with foam between. Sheetrock over the works. He did some rewiring
at the same time, dropping some romex in was easy. Had knob and tube
before with a little BX mixed in. We made up a hot-wire cutter with
an old train transformer and some nichrome, worked well enough to rip
foam strips and cut to length.

As far as the other poster's comments on shingle color, we'd reroofed
with a mostly white pattern, made a huge difference in that walk-in
attic heat radiated into the livingroom below. Must have cut the temp
in the attic by at least 20 degrees. Later on, they stuck a big fan
in the attic window for the summers, that really made a difference.

Stan

"rangerssuck" wrote in message
...
On Jul 27, 10:20 am, "Existential Angst" wrote:
Awl --

Recently, on one of these How They Do It ditties, they featured but more
Dubai profligacy, this time indoor skiing in the middle of the effing
desert.

The key to the insulation, they explained, was a huge air gap, asserting
that air -- caveat: trapped non-moving air -- was among the best
insulators.

First, is this true? Before I insulated my roof, that air would become
blisteringly hot, and it didn't seem to be moving much. That attic seemed
like a pretty good air gap to me, and it didn't seem to be doing much
insulating.

Second, I seem to remember one strategy where push/pull fans were used
with
air gaps in a roof-type situation, to keep air flowing, to reduce the
heating transfer, like what accumulated in my attic -- ie, the exact
opposite of static air.

Now mebbe air behaves differently in conduction vs. *radiant* heat from
roof-type situations that is making the attic so hot, not hot air
itself --
if the two can be distinguished wrt air.

iirc, the Dubai ditty used reflection, insulation, AND that big air
gap.....

But I've read about this insulating property of air before, so I'm
wondering
how it might be employed in a house.
It would seem that if air itself was so good, solid insulation wouldn't be
so high a priority

I wonder what mooslims think about Dubai.....
--
EA

You've got a bunch of apples and oranges mixed up in your fruit salad.
In your attic, you have a roof which is being heated by the sun. Then
you have convection, which mixes up the attic air and brings it in
contact with the lower floor's ceiling. The object of insulation
material is to keep the air still, to (virtually) eliminate the
convection.
================================================== ==

If I saw/understood correctly, the air gap space in this Dubai skiing thing
was the size of an airplane hangar.
=======



a properly vented attic space should have a considerably lower
temperature. Air is drawn into the soffit vents and expelled through
the ridge vent. Even better is a powered ventilator or, the push-pull
fans you mentioned. In the ventilated space, the sun-heated air is
replaced with cooler ambient outside air. This has nothing to do with
the insulation value of the air, just its temperature.

Besides the house cooling issues, it is generally a good thing for the
logevity of the roofing materials to keep the inside attic temperature
as close as possible to the outside temperature.
================================================== =====

Yeah, I've heard that too.
I've got a slate roof, I wonder if insulated the rafter space was the best
move.
--
EA









A reflective roof would make a huge difference. I don't understand the
fascination with black (or othr dark color) roofing shingles.

On Jul 27, 10:33*am, rangerssuck wrote:
On Jul 27, 11:25*am, rangerssuck wrote:









On Jul 27, 10:20*am, "Existential Angst" wrote:

Awl --

Recently, on one of these How They Do It ditties, they featured but more
Dubai profligacy, this time indoor skiing in the middle of the effing
desert.

The key to the insulation, they explained, was a huge air gap, asserting
that air -- caveat: *trapped non-moving air -- was among the best
insulators.

First, is this true? *Before I insulated my roof, that air would become
blisteringly hot, and it didn't seem to be moving much. *That attic seemed
like a pretty good air gap to me, and it didn't seem to be doing much
insulating.

Second, I seem to remember one strategy where push/pull fans were used with
air gaps in a roof-type situation, to keep air flowing, to reduce the
heating transfer, like what accumulated in my attic -- ie, the exact
opposite of static air.

Now mebbe air behaves differently in conduction vs. *radiant* heat from
roof-type situations that is making the attic so hot, not hot air itself -- *
if the two can be distinguished wrt air.

iirc, the Dubai ditty used reflection, insulation, AND that big air gap.....

But I've read about this insulating property of air before, so I'm wondering
how it might be employed in a house.
It would seem that if air itself was so good, solid insulation wouldn't be
so high a priority

I wonder what mooslims think about Dubai.....
--
EA

You've got a bunch of apples and oranges mixed up in your fruit salad.
In your attic, you have a roof which is being heated by the sun. Then
you have convection, which mixes up the attic air and brings it in
contact with the lower floor's ceiling. The object of insulation
material is to keep the air still, to (virtually) eliminate the
convection.

a properly vented attic space should have a considerably lower
temperature. Air is drawn into the soffit vents and expelled through
the ridge vent. Even better is a powered ventilator or, the push-pull
fans you mentioned. In the ventilated space, the sun-heated air is
replaced with cooler ambient outside air. This has nothing to do with
the insulation value of the air, just its temperature.

Besides the house cooling issues, it is generally a good thing for the
logevity of the roofing materials to keep the inside attic temperature
as close as possible to the outside temperature.

A reflective roof would make a huge difference. I don't understand the
fascination with black (or othr dark color) roofing shingles.- Hide quoted text -

- Show quoted text -

Now, having said all that, I have a related question:

My attic floor is insulated, but rather poorly. Adding more insulation
in the attic would not be easy. I am getting ready to repair the
ceilings in two bedrooms. The plaster is badly cracked and there are
definitely some broken keys (plaster / wood lath). The standard
parctice is to install furring strips and sheetrock over the plaster.
What I'm thinking about is adding a couple of inches of ridgid foam
insulation between the plaster and sheetrock.

I'd use screws and plaster washers to secure the existing ceiling to
the joists. Then use screws with fender washers to secure the
insulation, and then screw the sheetrock through the wholew mess to
the joists with, say, 3 1/2" sheetrock screws. I CAN afford to give up
a couple of inches of ceiling height.

Is this plan at all sane?

It will work OK if you can put up with wavy sheetrock. Probably
wouldn't be that noticeable. This assumes the plaster is unstable and
therefore the furring strips may not be quite level. Having BTDT, I
did like most everyone else does and gat rid of the old cracked
plaster and lath. On most jobs the old joists were nearly all true, so
the drywall crew were quickly done and the odds and ends I did turned
out well. Your plan may be rather labor intensive, so choose
carefully.

Joe

On Jul 27, 10:20*am, "Existential Angst" wrote:
Awl --

Recently, on one of these How They Do It ditties, they featured but more
Dubai profligacy, this time indoor skiing in the middle of the effing
desert.

The key to the insulation, they explained, was a huge air gap, asserting
that air -- caveat: *trapped non-moving air -- was among the best
insulators.

First, is this true? *Before I insulated my roof, that air would become
blisteringly hot, and it didn't seem to be moving much. *That attic seemed
like a pretty good air gap to me, and it didn't seem to be doing much
insulating.

Second, I seem to remember one strategy where push/pull fans were used with
air gaps in a roof-type situation, to keep air flowing, to reduce the
heating transfer, like what accumulated in my attic -- ie, the exact
opposite of static air.

Now mebbe air behaves differently in conduction vs. *radiant* heat from
roof-type situations that is making the attic so hot, not hot air itself -- *
if the two can be distinguished wrt air.

iirc, the Dubai ditty used reflection, insulation, AND that big air gap......

But I've read about this insulating property of air before, so I'm wondering
how it might be employed in a house.

It actually is employed in your house if you have fiberglass
insulation.
The fiberglass essentially traps air within the fiberglass so that it
cannot move. Air that does not move will not transfer heat very
effectively.
That's why if you crush the insulation down and compress it, you
greatly reduce the R value.

How that applies to the Dubai ski facility, I'm not clear on. I
agree with your reasoning that if it's just a closed air space
similar to an attic, it won't work, because the air will move
via convection.






It would seem that if air itself was so good, solid insulation wouldn't be
so high a priority

I wonder what mooslims think about Dubai.....
--
EA

In article ,
says...

Awl --

Recently, on one of these How They Do It ditties, they featured but more
Dubai profligacy, this time indoor skiing in the middle of the effing
desert.

The key to the insulation, they explained, was a huge air gap, asserting
that air -- caveat: trapped non-moving air -- was among the best
insulators.

First, is this true?

Yep.

Before I insulated my roof, that air would become
blisteringly hot, and it didn't seem to be moving much. That attic seemed
like a pretty good air gap to me, and it didn't seem to be doing much
insulating.

The attic would have a convection cell going unless there was something
in it that prevented convection.

Fiberglass, styrofoam, down, etc, all trap air--that's where their
insulating value comes from.

Second, I seem to remember one strategy where push/pull fans were used with
air gaps in a roof-type situation, to keep air flowing, to reduce the
heating transfer, like what accumulated in my attic -- ie, the exact
opposite of static air.

If it's just recirculating the air in the attic it isn't going to do
much, if it's moving outside air in and inside air out then it's
providing cooling--generally the air temperature will be less than the
surface temperature.

Now mebbe air behaves differently in conduction vs. *radiant* heat from
roof-type situations that is making the attic so hot, not hot air itself --
if the two can be distinguished wrt air.

Convection is different from both conduction and radiation. Air heats
by convection.

iirc, the Dubai ditty used reflection, insulation, AND that big air gap.....

But I've read about this insulating property of air before, so I'm wondering
how it might be employed in a house.
It would seem that if air itself was so good, solid insulation wouldn't be
so high a priority

The "solid" insulation is to keep the air from moving.


I wonder what mooslims think about Dubai.....

rangerssuck wrote:

A reflective roof would make a huge difference. I don't understand the
fascination with black (or othr dark color) roofing shingles.

Drive around your neighborhood or town. Do you see ANY light-colored roofs?

The reason is cosmetic. A white roof will show the dirt/smog/particulates
that settle out of the air, making the roof look like a mud pie.

Heck, I've got to power-wash my brick veneer ever two or three years to get
the mung off of it. But as bad as that is, pity poor Rome.

The city has pressure-washing crews that travel about the city cleaning
statues and marble artworks from the stuff settling on them from the air
(and I don't mean pigeons).

On Jul 27, 10:33*am, rangerssuck wrote:
On Jul 27, 11:25*am, rangerssuck wrote:









On Jul 27, 10:20*am, "Existential Angst" wrote:

Awl --

Recently, on one of these How They Do It ditties, they featured but more
Dubai profligacy, this time indoor skiing in the middle of the effing
desert.

The key to the insulation, they explained, was a huge air gap, asserting
that air -- caveat: *trapped non-moving air -- was among the best
insulators.

First, is this true? *Before I insulated my roof, that air would become
blisteringly hot, and it didn't seem to be moving much. *That attic seemed
like a pretty good air gap to me, and it didn't seem to be doing much
insulating.

Second, I seem to remember one strategy where push/pull fans were used with
air gaps in a roof-type situation, to keep air flowing, to reduce the
heating transfer, like what accumulated in my attic -- ie, the exact
opposite of static air.

Now mebbe air behaves differently in conduction vs. *radiant* heat from
roof-type situations that is making the attic so hot, not hot air itself -- *
if the two can be distinguished wrt air.

iirc, the Dubai ditty used reflection, insulation, AND that big air gap.....

But I've read about this insulating property of air before, so I'm wondering
how it might be employed in a house.
It would seem that if air itself was so good, solid insulation wouldn't be
so high a priority

I wonder what mooslims think about Dubai.....
--
EA

You've got a bunch of apples and oranges mixed up in your fruit salad.
In your attic, you have a roof which is being heated by the sun. Then
you have convection, which mixes up the attic air and brings it in
contact with the lower floor's ceiling. The object of insulation
material is to keep the air still, to (virtually) eliminate the
convection.

a properly vented attic space should have a considerably lower
temperature. Air is drawn into the soffit vents and expelled through
the ridge vent. Even better is a powered ventilator or, the push-pull
fans you mentioned. In the ventilated space, the sun-heated air is
replaced with cooler ambient outside air. This has nothing to do with
the insulation value of the air, just its temperature.

Besides the house cooling issues, it is generally a good thing for the
logevity of the roofing materials to keep the inside attic temperature
as close as possible to the outside temperature.

A reflective roof would make a huge difference. I don't understand the
fascination with black (or othr dark color) roofing shingles.- Hide quoted text -

- Show quoted text -

Now, having said all that, I have a related question:

My attic floor is insulated, but rather poorly. Adding more insulation
in the attic would not be easy. I am getting ready to repair the
ceilings in two bedrooms. The plaster is badly cracked and there are
definitely some broken keys (plaster / wood lath). The standard
parctice is to install furring strips and sheetrock over the plaster.
What I'm thinking about is adding a couple of inches of ridgid foam
insulation between the plaster and sheetrock.

I'd use screws and plaster washers to secure the existing ceiling to
the joists. Then use screws with fender washers to secure the
insulation, and then screw the sheetrock through the wholew mess to
the joists with, say, 3 1/2" sheetrock screws. I CAN afford to give up
a couple of inches of ceiling height.

Is this plan at all sane?

I'm thinking of doing something similar on my ceiling. In 60% of my
house I've got a cathedral ceiling with 2 by 8 rafters packed full of
fiberglass insulation. I'd like to add some ventilation and increase
the R-factor. I'm thinking of removing the ceiling and the fiberglass
insulation, and then putting six inches of the pink insulation board
between the rafters. That would leave about an inch and a quarter of
space on top for air to go out a ridge vent. Then I'd add two inches
of foam board on the bottom face of the rafters with 1 by 3 boards
screwed perpendicular to the rafters to provide a base for the
drywall. I'll probably put in some radiant foil insulation as well.
This would take me from R-22 to R-40 something and provide some much
needed roof ventilation. (I'm in Minnesota.) I would lose about 3
inches of ceiling height and that might be a code problem at the short
walls.

In your case you might also want to put up boards to attach the
drywall. You might get too much flex going through the two inches of
foam. I saw something online about that when I was researching the
problem. The other issue is you'll be sandwiching the current plaster
ceiling between two moisture barriers (the existing one and the new
foam board one). However, I don't think that would be a big deal. You
could drill a few hundred holes in the current ceiling if you were
worried about that.

Good luck with the project.

dss

On Jul 27, 10:33*am, rangerssuck wrote:
On Jul 27, 11:25*am, rangerssuck wrote:





On Jul 27, 10:20*am, "Existential Angst" wrote:

Awl --

Recently, on one of these How They Do It ditties, they featured but more
Dubai profligacy, this time indoor skiing in the middle of the effing
desert.

The key to the insulation, they explained, was a huge air gap, asserting
that air -- caveat: *trapped non-moving air -- was among the best
insulators.

First, is this true? *Before I insulated my roof, that air would become
blisteringly hot, and it didn't seem to be moving much. *That attic seemed
like a pretty good air gap to me, and it didn't seem to be doing much
insulating.

Second, I seem to remember one strategy where push/pull fans were used with
air gaps in a roof-type situation, to keep air flowing, to reduce the
heating transfer, like what accumulated in my attic -- ie, the exact
opposite of static air.

Now mebbe air behaves differently in conduction vs. *radiant* heat from
roof-type situations that is making the attic so hot, not hot air itself -- *
if the two can be distinguished wrt air.

iirc, the Dubai ditty used reflection, insulation, AND that big air gap.....

But I've read about this insulating property of air before, so I'm wondering
how it might be employed in a house.
It would seem that if air itself was so good, solid insulation wouldn't be
so high a priority

I wonder what mooslims think about Dubai.....
--
EA

You've got a bunch of apples and oranges mixed up in your fruit salad.
In your attic, you have a roof which is being heated by the sun. Then
you have convection, which mixes up the attic air and brings it in
contact with the lower floor's ceiling. The object of insulation
material is to keep the air still, to (virtually) eliminate the
convection.

a properly vented attic space should have a considerably lower
temperature. Air is drawn into the soffit vents and expelled through
the ridge vent. Even better is a powered ventilator or, the push-pull
fans you mentioned. In the ventilated space, the sun-heated air is
replaced with cooler ambient outside air. This has nothing to do with
the insulation value of the air, just its temperature.

Besides the house cooling issues, it is generally a good thing for the
logevity of the roofing materials to keep the inside attic temperature
as close as possible to the outside temperature.

A reflective roof would make a huge difference. I don't understand the
fascination with black (or othr dark color) roofing shingles.- Hide quoted text -

- Show quoted text -

Now, having said all that, I have a related question:

My attic floor is insulated, but rather poorly. Adding more insulation
in the attic would not be easy. I am getting ready to repair the
ceilings in two bedrooms. The plaster is badly cracked and there are
definitely some broken keys (plaster / wood lath). The standard
parctice is to install furring strips and sheetrock over the plaster.
What I'm thinking about is adding a couple of inches of ridgid foam
insulation between the plaster and sheetrock.

I'd use screws and plaster washers to secure the existing ceiling to
the joists. Then use screws with fender washers to secure the
insulation, and then screw the sheetrock through the wholew mess to
the joists with, say, 3 1/2" sheetrock screws. I CAN afford to give up
a couple of inches of ceiling height.

Is this plan at all sane?- Hide quoted text -

- Show quoted text -

YES!

On Jul 27, 11:33*am, rangerssuck wrote:
On Jul 27, 11:25*am, rangerssuck wrote:

You've got a bunch of apples and oranges mixed up in your fruit salad.
In your attic, you have a roof which is being heated by the sun. Then
you have convection, which mixes up the attic air and brings it in
contact with the lower floor's ceiling. The object of insulation
material is to keep the air still, to (virtually) eliminate the
convection.

The object of some insulation, such as fiberglass batt, does for a
large part utilize trapped air to achieve it's overall R value. Rigid
insulation...not so much. But I agree with your point as far as
trapped air adding to the insulation value. Basically it's taking
another step down on the heat transfer hierarchy of efficiency -
taking the step down from convection to radiation through the trapped
air.

a properly vented attic space should have a considerably lower
temperature. Air is drawn into the soffit vents and expelled through
the ridge vent. Even better is a powered ventilator or, the push-pull
fans you mentioned. In the ventilated space, the sun-heated air is
replaced with cooler ambient outside air. This has nothing to do with
the insulation value of the air, just its temperature.

Besides the house cooling issues, it is generally a good thing for the
longevity of the roofing materials to keep the inside attic temperature
as close as possible to the outside temperature.

A reflective roof would make a huge difference. I don't understand the
fascination with black (or othr dark color) roofing shingles.

I think the dark roof thing has a lot to do with tradition and what
people are used to seeing. It also has to do with minimizing the
objectionable appearance of roof discoloration. A darker roof
usually 'wears' better.

Now, having said all that, I have a related question:

My attic floor is insulated, but rather poorly. Adding more insulation
in the attic would not be easy. I am getting ready to repair the
ceilings in two bedrooms. The plaster is badly cracked and there are
definitely some broken keys (plaster / wood lath). The standard
parctice is to install furring strips and sheetrock over the plaster.
What I'm thinking about is adding a couple of inches of ridgid foam
insulation between the plaster and sheetrock.

I'd use screws and plaster washers to secure the existing ceiling to
the joists. Then use screws with fender washers to secure the
insulation, and then screw the sheetrock through the wholew mess to
the joists with, say, 3 1/2" sheetrock screws. I CAN afford to give up
a couple of inches of ceiling height.

Is this plan at all sane?

Perfectly. Normally I'd be tempted to pull the old ceiling plaster
and lath, and start fresh, but with the insulation up there, and the
fact that it's the middle of the summer...I like your plan
better. Exactly how poorly insulated is your attic floor and
where is the house?

The rigid insulation at the ceiling level is a superior solution
overall. If your ceiling joists or rafters are on 16" centers, that's
getting near 15% of the overall ceiling area being taken up by
joists. Depending on your insulation, those joists might be a thermal
short circuit.

3 1/2" drywall screws won't work with the existing plaster and 2" of
rigid insulation and the new drywall ceiling. Even 4" screws are a
little short for my tastes in that situation.

R

On Wed, 27 Jul 2011 16:43:32 -0500, "HeyBub" wrote:

rangerssuck wrote:

A reflective roof would make a huge difference. I don't understand the
fascination with black (or othr dark color) roofing shingles.

Drive around your neighborhood or town. Do you see ANY light-colored roofs?

I see them. In fact, I used to have one (shingled the 2-1/2 car garage
myself). I guess it depends on where you live, but worse than mung from the
air is mold. It *really* shows up on light shingles.

The reason is cosmetic. A white roof will show the dirt/smog/particulates
that settle out of the air, making the roof look like a mud pie.

Heck, I've got to power-wash my brick veneer ever two or three years to get
the mung off of it. But as bad as that is, pity poor Rome.

The city has pressure-washing crews that travel about the city cleaning
statues and marble artworks from the stuff settling on them from the air
(and I don't mean pigeons).

On Jul 27, 10:20*am, "Existential Angst" wrote:
Awl --

Recently, on one of these How They Do It ditties, they featured but more
Dubai profligacy, this time indoor skiing in the middle of the effing
desert.

The key to the insulation, they explained, was a huge air gap, asserting
that air -- caveat: *trapped non-moving air -- was among the best
insulators.

First, is this true? *Before I insulated my roof, that air would become
blisteringly hot, and it didn't seem to be moving much. *That attic seemed
like a pretty good air gap to me, and it didn't seem to be doing much
insulating.

Second, I seem to remember one strategy where push/pull fans were used with
air gaps in a roof-type situation, to keep air flowing, to reduce the
heating transfer, like what accumulated in my attic -- ie, the exact
opposite of static air.

Now mebbe air behaves differently in conduction vs. *radiant* heat from
roof-type situations that is making the attic so hot, not hot air itself -- *
if the two can be distinguished wrt air.

iirc, the Dubai ditty used reflection, insulation, AND that big air gap......

But I've read about this insulating property of air before, so I'm wondering
how it might be employed in a house.
It would seem that if air itself was so good, solid insulation wouldn't be
so high a priority

I wonder what mooslims think about Dubai.....
--
EA

You insulated your roof. Ok. What I did in my garage was install
perforated reflective material to the roof joists. This does create an
extra few inches of air space. The dominant force in the summer is the
suns heat. When there is a large differential temperate, radiance
becomes dominant. I used to go in my garage and you could feel the
heat from the roof. Now, nothing. And of course it's a lot cooler
through the day. Eventually the temperature of the air becomes equal
to the outside through the day, but forget the baking effect.

Greg

"Existential Angst" wrote in message
...
Awl --

Recently, on one of these How They Do It ditties, they featured but more
Dubai profligacy, this time indoor skiing in the middle of the effing
desert.

The key to the insulation, they explained, was a huge air gap, asserting
that air -- caveat: trapped non-moving air -- was among the best
insulators.

First, is this true? Before I insulated my roof, that air would become
blisteringly hot, and it didn't seem to be moving much. That attic seemed
like a pretty good air gap to me, and it didn't seem to be doing much
insulating.

Second, I seem to remember one strategy where push/pull fans were used with
air gaps in a roof-type situation, to keep air flowing, to reduce the
heating transfer, like what accumulated in my attic -- ie, the exact
opposite of static air.

Now mebbe air behaves differently in conduction vs. *radiant* heat from
roof-type situations that is making the attic so hot, not hot air itself --
if the two can be distinguished wrt air.

iirc, the Dubai ditty used reflection, insulation, AND that big air gap.....

But I've read about this insulating property of air before, so I'm wondering
how it might be employed in a house.
It would seem that if air itself was so good, solid insulation wouldn't be
so high a priority

I wonder what mooslims think about Dubai.....
--
EA


No, it's not true as others have already responded.
Those shows are riddled with errors, which, I suspect come from liberal
arts majors writing/editing the scripts which the narrator just reads. Accuracy
in science or engineering doesn't seem to be high on their list of important
aspects of the show.
Art

On Wed, 27 Jul 2011 08:25:09 -0700 (PDT), rangerssuck
wrote:

snip

Besides the house cooling issues, it is generally a good thing for the
logevity of the roofing materials to keep the inside attic temperature
as close as possible to the outside temperature.

A reflective roof would make a huge difference. I don't understand the
fascination with black (or othr dark color) roofing shingles.

You'll want to check the numbers if using asphalt shingles. We are
considering a re-shingle job, and found that "white" shingles aren't
hugely better than black in reflectivity (they are slighly better,
though). A shiny metal roof might be very different, I dunno.

The manufacturer may give reflectivity values for various shingles.
--
Best -- Terry

Terry wrote:

You'll want to check the numbers if using asphalt shingles. We are
considering a re-shingle job, and found that "white" shingles aren't
hugely better than black in reflectivity (they are slighly better,
though). A shiny metal roof might be very different, I dunno.


Some places are difficult to get insurance if you have a metal roof
on your home.


--
It's easy to think outside the box, when you have a cutting torch.

zzzzzzzzzz wrote:
On Wed, 27 Jul 2011 16:43:32 -0500, "HeyBub"
wrote:

rangerssuck wrote:

A reflective roof would make a huge difference. I don't understand
the fascination with black (or othr dark color) roofing shingles.

Drive around your neighborhood or town. Do you see ANY light-colored
roofs?

I see them. In fact, I used to have one (shingled the 2-1/2 car
garage myself). I guess it depends on where you live, but worse than
mung from the air is mold. It *really* shows up on light shingles.


Ah, of course you're right. I'm in a metropolitan area - lot's of cars,
busses, trucks, heavy industry, and chickens driving Cadillacs to
Washington, D.C.

On Thu, 28 Jul 2011 11:05:42 -0400, "Michael A. Terrell"
wrote:


Terry wrote:

You'll want to check the numbers if using asphalt shingles. We are
considering a re-shingle job, and found that "white" shingles aren't
hugely better than black in reflectivity (they are slighly better,
though). A shiny metal roof might be very different, I dunno.


Some places are difficult to get insurance if you have a metal roof
on your home.

Where? Why? I would think it would lower the insurance. Lasts
longer, more durable, and more resistant to fire.

Jim

Jim Elbrecht wrote:

On Thu, 28 Jul 2011 11:05:42 -0400, "Michael A. Terrell"
wrote:


Terry wrote:

You'll want to check the numbers if using asphalt shingles. We are
considering a re-shingle job, and found that "white" shingles aren't
hugely better than black in reflectivity (they are slighly better,
though). A shiny metal roof might be very different, I dunno.


Some places are difficult to get insurance if you have a metal roof
on your home.

Where? Why? I would think it would lower the insurance. Lasts
longer, more durable, and more resistant to fire.


Florida. High winds. Harder to put out a house fire, since you can't
walk on it and cut holes to ventilate the building.


--
It's easy to think outside the box, when you have a cutting torch.

"Existential Angst" wrote:
Awl --

Recently, on one of these How They Do It ditties, they featured but more
Dubai profligacy, this time indoor skiing in the middle of the effing
desert.

The key to the insulation, they explained, was a huge air gap, asserting
that air -- caveat: trapped non-moving air -- was among the best
insulators.

First, is this true? Before I insulated my roof, that air would become
blisteringly hot, and it didn't seem to be moving much. That attic seemed
like a pretty good air gap to me, and it didn't seem to be doing much
insulating.

Second, I seem to remember one strategy where push/pull fans were used with
air gaps in a roof-type situation, to keep air flowing, to reduce the
heating transfer, like what accumulated in my attic -- ie, the exact
opposite of static air.

Now mebbe air behaves differently in conduction vs. *radiant* heat from
roof-type situations that is making the attic so hot, not hot air itself --
if the two can be distinguished wrt air.

iirc, the Dubai ditty used reflection, insulation, AND that big air gap.....

But I've read about this insulating property of air before, so I'm wondering
how it might be employed in a house.
It would seem that if air itself was so good, solid insulation wouldn't be
so high a priority

I wonder what mooslims think about Dubai.....

Vacuum is best, with two reflective sides. I never figured out argon a
heavy gas. I think air with humidity is worse than dry air.
Syrofoam is a little bit worse than some other foams. I could never figure
that out.
Fiberglass tends to be a little worse than cellulose because cellulose
stops air flow better.
I also think extra thin fiberglass is better. Corning used to make very
fine, no itch.
Insulating the roof will shorten the life of shingles, they get hotter.
Maybe if every building had reflective or plants, the world would cool
down.

Maybe someday I'll install reflective sheeting on the house like I did on
garage. First I need to cut openings in the wooden sofet where they
installed perforated aluminum over the wood. Well they did drill a couple
holes in the wood, here and there. Bought the house like that.

Greg

On Thu, 28 Jul 2011 10:09:34 -0500, "HeyBub" wrote:

wrote:
On Wed, 27 Jul 2011 16:43:32 -0500, "HeyBub"
wrote:

rangerssuck wrote:

A reflective roof would make a huge difference. I don't understand
the fascination with black (or othr dark color) roofing shingles.

Drive around your neighborhood or town. Do you see ANY light-colored
roofs?

I see them. In fact, I used to have one (shingled the 2-1/2 car
garage myself). I guess it depends on where you live, but worse than
mung from the air is mold. It *really* shows up on light shingles.


Ah, of course you're right. I'm in a metropolitan area - lot's of cars,
busses, trucks, heavy industry, and chickens driving Cadillacs to
Washington, D.C.

I was living in NY (~70mi North of NYC) at the time. There aren't any white
roofs down here but I suspect it's because of the red clay.

On Jul 27, 8:33*am, rangerssuck wrote:
On Jul 27, 11:25*am, rangerssuck wrote:









On Jul 27, 10:20*am, "Existential Angst" wrote:

Awl --

Recently, on one of these How They Do It ditties, they featured but more
Dubai profligacy, this time indoor skiing in the middle of the effing
desert.

The key to the insulation, they explained, was a huge air gap, asserting
that air -- caveat: *trapped non-moving air -- was among the best
insulators.

First, is this true? *Before I insulated my roof, that air would become
blisteringly hot, and it didn't seem to be moving much. *That attic seemed
like a pretty good air gap to me, and it didn't seem to be doing much
insulating.

Second, I seem to remember one strategy where push/pull fans were used with
air gaps in a roof-type situation, to keep air flowing, to reduce the
heating transfer, like what accumulated in my attic -- ie, the exact
opposite of static air.

Now mebbe air behaves differently in conduction vs. *radiant* heat from
roof-type situations that is making the attic so hot, not hot air itself -- *
if the two can be distinguished wrt air.

iirc, the Dubai ditty used reflection, insulation, AND that big air gap.....

But I've read about this insulating property of air before, so I'm wondering
how it might be employed in a house.
It would seem that if air itself was so good, solid insulation wouldn't be
so high a priority

I wonder what mooslims think about Dubai.....
--
EA

You've got a bunch of apples and oranges mixed up in your fruit salad.
In your attic, you have a roof which is being heated by the sun. Then
you have convection, which mixes up the attic air and brings it in
contact with the lower floor's ceiling. The object of insulation
material is to keep the air still, to (virtually) eliminate the
convection.

a properly vented attic space should have a considerably lower
temperature. Air is drawn into the soffit vents and expelled through
the ridge vent. Even better is a powered ventilator or, the push-pull
fans you mentioned. In the ventilated space, the sun-heated air is
replaced with cooler ambient outside air. This has nothing to do with
the insulation value of the air, just its temperature.

Besides the house cooling issues, it is generally a good thing for the
logevity of the roofing materials to keep the inside attic temperature
as close as possible to the outside temperature.

A reflective roof would make a huge difference. I don't understand the
fascination with black (or othr dark color) roofing shingles.- Hide quoted text -

- Show quoted text -

Now, having said all that, I have a related question:

My attic floor is insulated, but rather poorly. Adding more insulation
in the attic would not be easy. I am getting ready to repair the
ceilings in two bedrooms. The plaster is badly cracked and there are
definitely some broken keys (plaster / wood lath). The standard
parctice is to install furring strips and sheetrock over the plaster.
What I'm thinking about is adding a couple of inches of ridgid foam
insulation between the plaster and sheetrock.

I'd use screws and plaster washers to secure the existing ceiling to
the joists. Then use screws with fender washers to secure the
insulation, and then screw the sheetrock through the wholew mess to
the joists with, say, 3 1/2" sheetrock screws. I CAN afford to give up
a couple of inches of ceiling height.

Is this plan at all sane?

Is this plan at all sane?

Generally speaking.... yes.

I'm not sure I'd do it exactly the way you propose but your idea is
workable.

RIgid foam could give you an additional R-14 with only ~2".

Depending on your local climate vapor barrier issues might be
important.

cheers
Bob

On Jul 27, 10:20*am, "Existential Angst" wrote:
It would seem that if air itself was so good, solid insulation wouldn't be
so high a priority

Neither fiberglass nor Styrofoam are "solid". They are basically air
with a tiny bit of structure to keep that air from moving (much)...

Even if your attic were hermetically sealed, the air in it would be
moving all over the place (though too slowly to notice).

Michael A. Terrell" wrote:


Jim Elbrecht wrote:

On Thu, 28 Jul 2011 11:05:42 -0400, "Michael A. Terrell"
wrote:


Terry wrote:

You'll want to check the numbers if using asphalt shingles. We are
considering a re-shingle job, and found that "white" shingles aren't
hugely better than black in reflectivity (they are slighly better,
though). A shiny metal roof might be very different, I dunno.


Some places are difficult to get insurance if you have a metal roof
on your home.

Where? Why? I would think it would lower the insurance. Lasts
longer, more durable, and more resistant to fire.


Florida. High winds. Harder to put out a house fire, since you can't
walk on it and cut holes to ventilate the building.

Wind makes sense- we rarely have roof-ripping winds in my neck of the
woods-- But our firemen have ladders & don't walk around on our
rather steep rooves. [roofs?- suit yourself, I looked it up because
rooves looked weird-- both work]

Jim

On Jul 28, 12:33*pm, "Michael A. Terrell"
wrote:
Jim Elbrecht wrote:
On Thu, 28 Jul 2011 11:05:42 -0400, "Michael A. Terrell" wrote:
Terry wrote:

You'll want to check the numbers if using asphalt shingles. *We are
considering a re-shingle job, and found that "white" shingles aren't
hugely better than black in reflectivity (they are slighly better,
though). * A shiny metal roof might be very different, I dunno.

* Some places are difficult to get insurance if you have a metal roof
on your home.

Where? *Why? * I would think it would lower the insurance. *Lasts
longer, more durable, and more resistant to fire.

* *Florida. High winds. Harder to put out a house fire, since you can't
walk on it and cut holes to ventilate the building.

There are a number of metal roofing systems that have been approved by
Dade County for high winds, and if it's good enough for Dade, it's
good enough for your application.

Impact resistance might be an insurance consideration for hail damage,
but there are metal roofing systems that have that...errr...covered as
well:
http://www.tdi.state.tx.us/home/roofingx.html

I know of no fire rating criteria that requires a building envelope
component to be easily compromised to improve firefighting access. If
you could provide a citation, that would be grand.

R

On Jul 28, 11:49*pm, Larry Fishel wrote:
On Jul 27, 10:20*am, "Existential Angst" wrote:

It would seem that if air itself was so good, solid insulation wouldn't be
so high a priority

Neither fiberglass nor Styrofoam are "solid". They are basically air
with a tiny bit of structure to keep that air from moving (much)...

Exactly. And they rely on the fact that stationary air is in fact a
poor conductor of heat.




Even if your attic were hermetically sealed, the air in it would be
moving all over the place (though too slowly to notice).

wrote in message
...
On Jul 28, 11:49 pm, Larry Fishel wrote:
On Jul 27, 10:20 am, "Existential Angst" wrote:

It would seem that if air itself was so good, solid insulation wouldn't
be
so high a priority

Neither fiberglass nor Styrofoam are "solid". They are basically air
with a tiny bit of structure to keep that air from moving (much)...

Exactly. And they rely on the fact that stationary air is in fact a
poor conductor of heat.

Another way to explain it is that there are two variables that control how
effective trapped air can be as an insulator. One is preventing mixing and
convection -- movement of the air, for practical purposes. Therefore, small
pockets are more efficient than big ones. The other is the relative
conductivity and relative volume of the entrapping medium: Plastics usually
are better than glass, which is better than metal, etc.

So fine, closed-cell foam is an extremely efficient insulator. Fiberglass
batts are relatively less so, but still are quite good because a dense
network of it is very good at preventing internal movement. Nanogel, which
is a type of aerogel, is one of the best that use air as the insulating
medium. (Most other aerogels have another gas in the pores.)


Even if your attic were hermetically sealed, the air in it would be
moving all over the place (though too slowly to notice).

On Jul 27, 4:04*pm, RicodJour wrote:
On Jul 27, 11:33*am, rangerssuck wrote:

On Jul 27, 11:25*am, rangerssuck wrote:

You've got a bunch of apples and oranges mixed up in your fruit salad..
In your attic, you have a roof which is being heated by the sun. Then
you have convection, which mixes up the attic air and brings it in
contact with the lower floor's ceiling. The object of insulation
material is to keep the air still, to (virtually) eliminate the
convection.

The object of some insulation, such as fiberglass batt, does for a
large part utilize trapped air to achieve it's overall R value. *Rigid
insulation...not so much. *But I agree with your point as far as
trapped air adding to the insulation value. *Basically it's taking
another step down on the heat transfer hierarchy of efficiency -
taking the step down from convection to radiation through the trapped
air.

a properly vented attic space should have a considerably lower
temperature. Air is drawn into the soffit vents and expelled through
the ridge vent. Even better is a powered ventilator or, the push-pull
fans you mentioned. In the ventilated space, the sun-heated air is
replaced with cooler ambient outside air. This has nothing to do with
the insulation value of the air, just its temperature.

Besides the house cooling issues, it is generally a good thing for the
longevity of the roofing materials to keep the inside attic temperature
as close as possible to the outside temperature.

A reflective roof would make a huge difference. I don't understand the
fascination with black (or othr dark color) roofing shingles.

I think the dark roof thing has a lot to do with tradition and what
people are used to seeing. *It also has to do with minimizing the
objectionable appearance of roof discoloration. *A darker roof
usually *'wears' better.









Now, having said all that, I have a related question:

My attic floor is insulated, but rather poorly. Adding more insulation
in the attic would not be easy. I am getting ready to repair the
ceilings in two bedrooms. The plaster is badly cracked and there are
definitely some broken keys (plaster / wood lath). The standard
parctice is to install furring strips and sheetrock over the plaster.
What I'm thinking about is adding a couple of inches of ridgid foam
insulation between the plaster and sheetrock.

I'd use screws and plaster washers to secure the existing ceiling to
the joists. Then use screws with fender washers to secure the
insulation, and then screw the sheetrock through the wholew mess to
the joists with, say, 3 1/2" sheetrock screws. I CAN afford to give up
a couple of inches of ceiling height.

Is this plan at all sane?

Perfectly. *Normally I'd be tempted to pull the old ceiling plaster
and lath, and start fresh, but with the insulation up there, and the
fact that it's the middle of the summer...I like your plan
better. * *Exactly how poorly insulated is your attic floor and
where is the house?

The rigid insulation at the ceiling level is a superior solution
overall. *If your ceiling joists or rafters are on 16" centers, that's
getting near 15% of the overall ceiling area being taken up by
joists. *Depending on your insulation, those joists might be a thermal
short circuit.

3 1/2" drywall screws won't work with the existing plaster and 2" of
rigid insulation and the new drywall ceiling. *Even 4" screws are a
little short for my tastes in that situation.

R

Rico-

Good point about the "thermal bridging" ....

OP-

I'd be inclined to take down the ceiling, remove the existing
insulation
and replace it with rigid foam between the existing joists.
If the joists are 2x6's you could get R-30.

Depending on your locale this might be enough or you could do another
inch or two below the joists and go even higher.

Vapor barrier issue could be addressed at the bottom surface of the
insulation or the surface of the draywall.

cheers
Bob

On Jul 27, 6:49*pm, "Artemus" wrote:
"Existential Angst" wrote in message

...







Awl --

Recently, on one of these How They Do It ditties, they featured but more
Dubai profligacy, this time indoor skiing in the middle of the effing
desert.

The key to the insulation, they explained, was a huge air gap, asserting
that air -- caveat: *trapped non-moving air -- was among the best
insulators.

First, is this true? *Before I insulated my roof, that air would become
blisteringly hot, and it didn't seem to be moving much. *That attic seemed
like a pretty good air gap to me, and it didn't seem to be doing much
insulating.

Second, I seem to remember one strategy where push/pull fans were used with
air gaps in a roof-type situation, to keep air flowing, to reduce the
heating transfer, like what accumulated in my attic -- ie, the exact
opposite of static air.

Now mebbe air behaves differently in conduction vs. *radiant* heat from
roof-type situations that is making the attic so hot, not hot air itself --
if the two can be distinguished wrt air.

iirc, the Dubai ditty used reflection, insulation, AND that big air gap......

But I've read about this insulating property of air before, so I'm wondering
how it might be employed in a house.
It would seem that if air itself was so good, solid insulation wouldn't be
so high a priority

I wonder what mooslims think about Dubai.....
--
EA

No, it's not true as others have already responded.
Those shows are riddled with errors, which, I suspect come from liberal
arts majors writing/editing the scripts which the narrator just reads. *Accuracy
in science or engineering doesn't seem to be high on their list of important
aspects of the show.
Art

Why particularly do you suspect the people you are indicting (without
evidence)? Please defend your thesis with actual data.

HB

On Jul 29, 4:49*am, Larry Fishel wrote:
On Jul 27, 10:20*am, "Existential Angst" wrote:

It would seem that if air itself was so good, solid insulation wouldn't be
so high a priority

Neither fiberglass nor Styrofoam are "solid". They are basically air
with a tiny bit of structure to keep that air from moving (much)...

Even if your attic were hermetically sealed, the air in it would be
moving all over the place (though too slowly to notice).

There are rigid foam boards available that do not contain air but
other gases. CO2 and refrigerants mostly. They are better than air as
an insulator.

On Fri, 29 Jul 2011 12:39:46 -0400, Ed Huntress wrote:
wrote ...
On Jul 28, 11:49 pm, Larry Fishel wrote:
On Jul 27, 10:20 am, "Existential Angst" fit... wrote:

It would seem that if air itself was so good, solid insulation
wouldn't be so high a priority

Neither fiberglass nor Styrofoam are "solid". They are basically air
with a tiny bit of structure to keep that air from moving (much)...

Exactly. And they rely on the fact that stationary air is in fact a
poor conductor of heat.

Another way to explain it is that there are two variables that control
how effective trapped air can be as an insulator. One is preventing
mixing and convection -- movement of the air, for practical purposes.
Therefore, small pockets are more efficient than big ones. The other is
the relative conductivity and relative volume of the entrapping medium:
Plastics usually are better than glass, which is better than metal, etc.

I contend that as a practical matter, "small pockets are more efficient
than big ones" does not remain true as cell size shrinks to zero.
Instead (for any given medium and filler gas) efficiency improves as
size decreases to some point, after which efficiency gets worse, due
to increased importance of heat conduction relative to convection as
size decreases. With an ideal medium, the ratio need not change,
because ideally the ratio of gas volume to medium volume can remain
constant as cell size shrinks and as constant strength (or, at least,
constant cross section of medium) is maintained. But as a practical
matter, after cell wall thickness reaches some minimal amount, it
cannot shrink further as cell size decreases.

[snip re aerogels & nanogel]

Makers of "cenospheres" are quite proud of their products -- see
eg http://www.isbu-info.org/all_about_ceramic_insulation.htm and
http://www.democraticunderground.com/discuss/duboard.php?az=view_all&address=115x89276

--
jiw

"James Waldby" wrote in message
...
On Fri, 29 Jul 2011 12:39:46 -0400, Ed Huntress wrote:
wrote ...
On Jul 28, 11:49 pm, Larry Fishel wrote:
On Jul 27, 10:20 am, "Existential Angst" fit... wrote:

It would seem that if air itself was so good, solid insulation
wouldn't be so high a priority

Neither fiberglass nor Styrofoam are "solid". They are basically air
with a tiny bit of structure to keep that air from moving (much)...

Exactly. And they rely on the fact that stationary air is in fact a
poor conductor of heat.

Another way to explain it is that there are two variables that control
how effective trapped air can be as an insulator. One is preventing
mixing and convection -- movement of the air, for practical purposes.
Therefore, small pockets are more efficient than big ones. The other is
the relative conductivity and relative volume of the entrapping medium:
Plastics usually are better than glass, which is better than metal, etc.

I contend that as a practical matter, "small pockets are more efficient
than big ones" does not remain true as cell size shrinks to zero.
Instead (for any given medium and filler gas) efficiency improves as
size decreases to some point, after which efficiency gets worse, due
to increased importance of heat conduction relative to convection as
size decreases.
With an ideal medium, the ratio need not change,
because ideally the ratio of gas volume to medium volume can remain
constant as cell size shrinks and as constant strength (or, at least,
constant cross section of medium) is maintained. But as a practical
matter, after cell wall thickness reaches some minimal amount, it
cannot shrink further as cell size decreases.

Sure. But the R value of polyurethane foam, for example, increases as the
pore size diminishes to the practical minimum you can obtain and still have
continuous foam.

But that practical limit diminishes further with aerogels, including
nanogel, because the thickness of the entraining walls can be vanishingly
small. And then you get even better R values.


[snip re aerogels & nanogel]

Makers of "cenospheres" are quite proud of their products -- see
eg http://www.isbu-info.org/all_about_ceramic_insulation.htm and
http://www.democraticunderground.com/discuss/duboard.php?az=view_all&address=115x89276

--
jiw

RicodJour wrote:

On Jul 28, 12:33 pm, "Michael A. Terrell"
wrote:
Jim Elbrecht wrote:
On Thu, 28 Jul 2011 11:05:42 -0400, "Michael A. Terrell" wrote:
Terry wrote:

You'll want to check the numbers if using asphalt shingles. We are
considering a re-shingle job, and found that "white" shingles aren't
hugely better than black in reflectivity (they are slighly better,
though). A shiny metal roof might be very different, I dunno.

Some places are difficult to get insurance if you have a metal roof
on your home.

Where? Why? I would think it would lower the insurance. Lasts
longer, more durable, and more resistant to fire.

Florida. High winds. Harder to put out a house fire, since you can't
walk on it and cut holes to ventilate the building.

There are a number of metal roofing systems that have been approved by
Dade County for high winds, and if it's good enough for Dade, it's
good enough for your application.

Impact resistance might be an insurance consideration for hail damage,
but there are metal roofing systems that have that...errr...covered as
well:
http://www.tdi.state.tx.us/home/roofingx.html

I know of no fire rating criteria that requires a building envelope
component to be easily compromised to improve firefighting access. If
you could provide a citation, that would be grand.



My dad had a house in Lake County and couldn't get insurance because
of the metal roof. They all told him to replace it with a shingle roof,
or they couldn't insure him. Of course, Dade county approves of all
kinds of construction that other places won't accept. I know people who
left there after Andrew. Houses less than two years old were badly
damaged, yet passed al hurricane rated inspections. Afterwards, he
damage revealed all kinds of substandard work. Curiously, all the
inspectors involved had 'retired' and couldn't be located.



--
It's easy to think outside the box, when you have a cutting torch.

In article ,
says...

RicodJour wrote:

On Jul 28, 12:33 pm, "Michael A. Terrell"
wrote:
Jim Elbrecht wrote:
On Thu, 28 Jul 2011 11:05:42 -0400, "Michael A. Terrell" wrote:
Terry wrote:

You'll want to check the numbers if using asphalt shingles. We are
considering a re-shingle job, and found that "white" shingles aren't
hugely better than black in reflectivity (they are slighly better,
though). A shiny metal roof might be very different, I dunno.

Some places are difficult to get insurance if you have a metal roof
on your home.

Where? Why? I would think it would lower the insurance. Lasts
longer, more durable, and more resistant to fire.

Florida. High winds. Harder to put out a house fire, since you can't
walk on it and cut holes to ventilate the building.

There are a number of metal roofing systems that have been approved by
Dade County for high winds, and if it's good enough for Dade, it's
good enough for your application.

Impact resistance might be an insurance consideration for hail damage,
but there are metal roofing systems that have that...errr...covered as
well:
http://www.tdi.state.tx.us/home/roofingx.html

I know of no fire rating criteria that requires a building envelope
component to be easily compromised to improve firefighting access. If
you could provide a citation, that would be grand.



My dad had a house in Lake County and couldn't get insurance because
of the metal roof. They all told him to replace it with a shingle roof,
or they couldn't insure him.

Perhaps he should have called State Farm. They list 20 pages of metal
roofs for which they offer discounts. To get the discount though you
have to take a cosmetic damage waiver--I guess they don't want to pay
for every little dent.

House I grew up in in Nassau County had a metal roof. Never any problem
getting insurance.

Of course, Dade county approves of all
kinds of construction that other places won't accept. I know people who
left there after Andrew. Houses less than two years old were badly
damaged, yet passed al hurricane rated inspections. Afterwards, he
damage revealed all kinds of substandard work. Curiously, all the
inspectors involved had 'retired' and couldn't be located.

Dade County changed the building code radically after Andrew you know,
based on lessons learned, and it is one of the toughest in the country
now.

"J. Clarke" wrote:

In article ,
says...

RicodJour wrote:

On Jul 28, 12:33 pm, "Michael A. Terrell"
wrote:
Jim Elbrecht wrote:
On Thu, 28 Jul 2011 11:05:42 -0400, "Michael A. Terrell" wrote:
Terry wrote:

You'll want to check the numbers if using asphalt shingles. We are
considering a re-shingle job, and found that "white" shingles aren't
hugely better than black in reflectivity (they are slighly better,
though). A shiny metal roof might be very different, I dunno.

Some places are difficult to get insurance if you have a metal roof
on your home.

Where? Why? I would think it would lower the insurance. Lasts
longer, more durable, and more resistant to fire.

Florida. High winds. Harder to put out a house fire, since you can't
walk on it and cut holes to ventilate the building.

There are a number of metal roofing systems that have been approved by
Dade County for high winds, and if it's good enough for Dade, it's
good enough for your application.

Impact resistance might be an insurance consideration for hail damage,
but there are metal roofing systems that have that...errr...covered as
well:
http://www.tdi.state.tx.us/home/roofingx.html

I know of no fire rating criteria that requires a building envelope
component to be easily compromised to improve firefighting access. If
you could provide a citation, that would be grand.



My dad had a house in Lake County and couldn't get insurance because
of the metal roof. They all told him to replace it with a shingle roof,
or they couldn't insure him.

Perhaps he should have called State Farm.


I'm sure he did, since they insured his car at the time.


They list 20 pages of metal
roofs for which they offer discounts. To get the discount though you
have to take a cosmetic damage waiver--I guess they don't want to pay
for every little dent.


They never want to pay, but there are plenty of roof types they don't
want to insure. By listing '20 types' it sounds like they are
decorative styles over plywood or other construction instead of a plain
'Five V' roof on perlings and rafters.


House I grew up in in Nassau County had a metal roof. Never any problem
getting insurance.

Of course, Dade county approves of all
kinds of construction that other places won't accept. I know people who
left there after Andrew. Houses less than two years old were badly
damaged, yet passed al hurricane rated inspections. Afterwards, he
damage revealed all kinds of substandard work. Curiously, all the
inspectors involved had 'retired' and couldn't be located.

Dade County changed the building code radically after Andrew you know,
based on lessons learned, and it is one of the toughest in the country
now.


--
It's easy to think outside the box, when you have a cutting torch.

In article ,
says...

"J. Clarke" wrote:

In article ,
says...

RicodJour wrote:

On Jul 28, 12:33 pm, "Michael A. Terrell"
wrote:
Jim Elbrecht wrote:
On Thu, 28 Jul 2011 11:05:42 -0400, "Michael A. Terrell" wrote:
Terry wrote:

You'll want to check the numbers if using asphalt shingles. We are
considering a re-shingle job, and found that "white" shingles aren't
hugely better than black in reflectivity (they are slighly better,
though). A shiny metal roof might be very different, I dunno.

Some places are difficult to get insurance if you have a metal roof
on your home.

Where? Why? I would think it would lower the insurance. Lasts
longer, more durable, and more resistant to fire.

Florida. High winds. Harder to put out a house fire, since you can't
walk on it and cut holes to ventilate the building.

There are a number of metal roofing systems that have been approved by
Dade County for high winds, and if it's good enough for Dade, it's
good enough for your application.

Impact resistance might be an insurance consideration for hail damage,
but there are metal roofing systems that have that...errr...covered as
well:
http://www.tdi.state.tx.us/home/roofingx.html

I know of no fire rating criteria that requires a building envelope
component to be easily compromised to improve firefighting access. If
you could provide a citation, that would be grand.



My dad had a house in Lake County and couldn't get insurance because
of the metal roof. They all told him to replace it with a shingle roof,
or they couldn't insure him.

Perhaps he should have called State Farm.


I'm sure he did, since they insured his car at the time.


They list 20 pages of metal
roofs for which they offer discounts. To get the discount though you
have to take a cosmetic damage waiver--I guess they don't want to pay
for every little dent.


They never want to pay, but there are plenty of roof types they don't
want to insure. By listing '20 types' it sounds like they are
decorative styles over plywood or other construction instead of a plain
'Five V' roof on perlings and rafters.

I didn't say "20 types", I said 20 _pages_, listed by brand name and
manufacturer mostly.

House I grew up in in Nassau County had a metal roof. Never any problem
getting insurance.

Of course, Dade county approves of all
kinds of construction that other places won't accept. I know people who
left there after Andrew. Houses less than two years old were badly
damaged, yet passed al hurricane rated inspections. Afterwards, he
damage revealed all kinds of substandard work. Curiously, all the
inspectors involved had 'retired' and couldn't be located.

Dade County changed the building code radically after Andrew you know,
based on lessons learned, and it is one of the toughest in the country
now.