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