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effi
 
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Default engineering cathedral ceiling with 3.25" thick airspace?

would like to create a cathedral type ceiling in a small area of 24" on
center roof rafters 3.25" thick

within the 3.25 inches thick want: 1" airflow space; and 2.25" insulation

how can the 1" thick airflow space (between 2.25" insulation and underside
of roof decking, plywood) be created?

seems just putting 2.25" thick of insulation without some means to keep the
1" airflow space open might be a mistake

have considered chickenwire with small 1" thick blocks of wood glued to
underside of roof decking every foot or so to keep the space open



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willshak
 
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On 12/20/2004 8:22 PM US(ET), effi took fingers to keys, and typed the
following:

would like to create a cathedral type ceiling in a small area of 24" on
center roof rafters 3.25" thick

within the 3.25 inches thick want: 1" airflow space; and 2.25" insulation

how can the 1" thick airflow space (between 2.25" insulation and underside
of roof decking, plywood) be created?

seems just putting 2.25" thick of insulation without some means to keep the
1" airflow space open might be a mistake

have considered chickenwire with small 1" thick blocks of wood glued to
underside of roof decking every foot or so to keep the space open

They make formed foam spacers that go between rafters that will keep the
insulation away from the roof sheathing.
Check at the big stores.
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Greg O
 
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"effi" wrote in message
...
would like to create a cathedral type ceiling in a small area of 24" on
center roof rafters 3.25" thick

within the 3.25 inches thick want: 1" airflow space; and 2.25" insulation

how can the 1" thick airflow space (between 2.25" insulation and underside
of roof decking, plywood) be created?

seems just putting 2.25" thick of insulation without some means to keep

the
1" airflow space open might be a mistake



Seems to me that 2.25" of insulation is a mistake!
Greg


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effi
 
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"willshak" wrote in message
...
On 12/20/2004 8:22 PM US(ET), effi took fingers to keys, and typed the
following:

would like to create a cathedral type ceiling in a small area of 24" on
center roof rafters 3.25" thick

within the 3.25 inches thick want: 1" airflow space; and 2.25" insulation

how can the 1" thick airflow space (between 2.25" insulation and underside
of roof decking, plywood) be created?

seems just putting 2.25" thick of insulation without some means to keep
the 1" airflow space open might be a mistake

have considered chickenwire with small 1" thick blocks of wood glued to
underside of roof decking every foot or so to keep the space open

They make formed foam spacers that go between rafters that will keep the
insulation away from the roof sheathing.
Check at the big stores.


considered those, they probably won't be structurally strong enough in this
application

also considering 4" of fiberglass insulation with 1 1/2" or 2" pvc,
perforated along the length by drilling lots of holes, run centrally inside
the 4" fiberglass to provide air circulation instead of 1" open space above
2.25" of insulation



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effi
 
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"Greg O" wrote in message
...

"effi" wrote in message
...
would like to create a cathedral type ceiling in a small area of 24" on
center roof rafters 3.25" thick

within the 3.25 inches thick want: 1" airflow space; and 2.25" insulation

how can the 1" thick airflow space (between 2.25" insulation and
underside
of roof decking, plywood) be created?

seems just putting 2.25" thick of insulation without some means to keep

the
1" airflow space open might be a mistake



Seems to me that 2.25" of insulation is a mistake!
Greg


ya, am leaning towards 4" of glass compressed into the 3.25" space, with
perforated pvc pipe run centrally through it for air flow

hardie panel soffit board will be ceiling and provide some insulation factor
as well




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willshak
 
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On 12/21/2004 12:19 AM US(ET), effi took fingers to keys, and typed the
following:

"willshak" wrote in message
...


On 12/20/2004 8:22 PM US(ET), effi took fingers to keys, and typed the
following:



would like to create a cathedral type ceiling in a small area of 24" on
center roof rafters 3.25" thick

within the 3.25 inches thick want: 1" airflow space; and 2.25" insulation

how can the 1" thick airflow space (between 2.25" insulation and underside
of roof decking, plywood) be created?

seems just putting 2.25" thick of insulation without some means to keep
the 1" airflow space open might be a mistake

have considered chickenwire with small 1" thick blocks of wood glued to
underside of roof decking every foot or so to keep the space open



They make formed foam spacers that go between rafters that will keep the
insulation away from the roof sheathing.
Check at the big stores.



considered those, they probably won't be structurally strong enough in this
application

also considering 4" of fiberglass insulation with 1 1/2" or 2" pvc,
perforated along the length by drilling lots of holes, run centrally inside
the 4" fiberglass to provide air circulation instead of 1" open space above
2.25" of insulation

You've already ruled out solid foam panels then?
They come in various thicknesses, and widths to fit between 16" o.c, or
24" o.c. framing.
http://www.owenscorning.com/around/i...s/foamular.asp
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HerHusband
 
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Effi,

would like to create a cathedral type ceiling in a small area of 24"
on center roof rafters 3.25" thick
within the 3.25 inches thick want: 1" airflow space; and 2.25"
insulation


2.25" won't provide much in the way of insulation, especially in a ceiling
where it's needed most. You might get R-5 to R10 if you're real lucky.
That's a far cry from the R38 (in my area) that normally is required in
cathedral ceilings.

To maintain the airspace, just use the foam air baffles you can get from
Home Depot or most any lumber yard. The ones I used have little "bumps" in
the middle to prevent them from getting pushed against the roof sheathing
when you push the insulation in.

Alternatively, you could nail (or glue) some 1x boards (or strips of
foam insulation) along the sides of the rafters and span the gap with a
piece of plywood or hardboard.

If you MUST stick to that 2.25" insulation space, your best bet would be
solid foam insulation. It will provide the best R-value per inch, and
because of their rigidity will probably not need the air baffles above
them.

Compressing 4" insulation into the space won't work very well either. It's
the air that gets trapped in the fiberglass that provides the insulation
ability. If you compress the fiberglass, you greatly reduce the air spaces
and correspondingly the R-value.

If there's any way you can shim down the rafter space to gain more depth
(i.e. nail 2x3's on edge along the bottom of the rafters), you could put in
more insulation.

Alternatively, or in combination with the above method, you could go ahead
and fill up the available rafter bays, then frame a second roof on top of
the existing roof sheathing, providing the 1" air space there.

Finally, you may want to look into sprayed foam insulation. It'll provide
the best insulating ability for the space, and will completely seal off the
rafter bays. While this would also eliminate the 1" airspace, I hear it
works well because no air currents can flow within the space. It's a lot
like structural stress skin panels. Unfortunately, it's not a do-it-
yourself application.

Good luck!

Anthony
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Philip Lewis
 
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HerHusband writes:
sprayed foam insulation.

[...]
While this would also eliminate the 1" airspace,


I've considered doing this. The resulting roof is then known as a
"hot roof" and might not be code in the OP's area. It might also void
shingle warranty.

We are looking at vaulting our third floor ceiling to open the place
up. it is currently a combination of sloped and flat ceiling with an
unaccessible "attic" space above the flat parts.

The way i've considered doing it is to use a small can of foam to
"glue" the air channels in first... then spray with the foam to fill
the remainder of the cavity. I havn't found an answer as to if
this would be a "good idea" or not... but it seems it would seal well,
supply vent space, and have the higest insulation value.

Unfortunately, it's not a do-it-yourself application.

perhaps it is.... www.fomofoam.com is where i've been looking.
I'd love to find some other sources for price comparison. Anyone know
of any?

--
be safe.
flip
Ich habe keine Ahnung was das bedeutet, oder vielleicht doch?
Remove origin of the word spam from address to reply (leave "+")


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willshak
 
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On 12/21/2004 12:19 AM US(ET), effi took fingers to keys, and typed the
following:

"willshak" wrote in message
...


On 12/20/2004 8:22 PM US(ET), effi took fingers to keys, and typed the
following:



would like to create a cathedral type ceiling in a small area of 24" on
center roof rafters 3.25" thick

within the 3.25 inches thick want: 1" airflow space; and 2.25" insulation

how can the 1" thick airflow space (between 2.25" insulation and underside
of roof decking, plywood) be created?

seems just putting 2.25" thick of insulation without some means to keep
the 1" airflow space open might be a mistake

have considered chickenwire with small 1" thick blocks of wood glued to
underside of roof decking every foot or so to keep the space open



They make formed foam spacers that go between rafters that will keep the
insulation away from the roof sheathing.
Check at the big stores.



considered those, they probably won't be structurally strong enough in this
application

also considering 4" of fiberglass insulation with 1 1/2" or 2" pvc,
perforated along the length by drilling lots of holes, run centrally inside
the 4" fiberglass to provide air circulation instead of 1" open space above
2.25" of insulation


I've already responded to this in another message, but I just had a thought.
Instead of all these efforts to keep the insulation away from the
sheathing with Rube Goldberg ideas, how about you nail 2-1/2" x 2-1/2"
strips of wood to the current 2 x 4 joists, so that they are 2x5"
joists, and then use common 3-1/2" insulation stapled to the 1-1/2" faces?
That will give you a 1-1/2" gap between the insulation and the sheathing
which is the recommended gap.

--
Bill
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effi
 
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"HerHusband" wrote in message
...
Effi,

would like to create a cathedral type ceiling in a small area of 24"
on center roof rafters 3.25" thick
within the 3.25 inches thick want: 1" airflow space; and 2.25"
insulation


2.25" won't provide much in the way of insulation, especially in a ceiling
where it's needed most. You might get R-5 to R10 if you're real lucky.
That's a far cry from the R38 (in my area) that normally is required in
cathedral ceilings.

To maintain the airspace, just use the foam air baffles you can get from
Home Depot or most any lumber yard. The ones I used have little "bumps" in
the middle to prevent them from getting pushed against the roof sheathing
when you push the insulation in.

Alternatively, you could nail (or glue) some 1x boards (or strips of
foam insulation) along the sides of the rafters and span the gap with a
piece of plywood or hardboard.

If you MUST stick to that 2.25" insulation space, your best bet would be
solid foam insulation. It will provide the best R-value per inch, and
because of their rigidity will probably not need the air baffles above
them.

Compressing 4" insulation into the space won't work very well either. It's
the air that gets trapped in the fiberglass that provides the insulation
ability. If you compress the fiberglass, you greatly reduce the air spaces
and correspondingly the R-value.

If there's any way you can shim down the rafter space to gain more depth
(i.e. nail 2x3's on edge along the bottom of the rafters), you could put
in
more insulation.

Alternatively, or in combination with the above method, you could go ahead
and fill up the available rafter bays, then frame a second roof on top of
the existing roof sheathing, providing the 1" air space there.

Finally, you may want to look into sprayed foam insulation. It'll provide
the best insulating ability for the space, and will completely seal off
the
rafter bays. While this would also eliminate the 1" airspace, I hear it
works well because no air currents can flow within the space. It's a lot
like structural stress skin panels. Unfortunately, it's not a do-it-
yourself application.

Good luck!

Anthony



thought of shimming the rafters down (making them thicker) but didn't like
the idea of heavy hardie panel ceiling attached to 2x4's attached to 2x4's,
so thought about running 2x6's alongside the existing 2x4's, resulting in
5.25" to work with (aka the 6 in "2x6"), but would have to tie 2x6's into
existing framework at peak of roof and where rafters meet top of wall
framing, an involved process so was gonna try to get by with 3.25", see now
it won't work, may go with the 2x6's alongside, then:


layers from underside of plywood roof decking down as follows:

wood blocks 1" x 1" square x 1.25" thick glued to underside of plywood roof
decking staggered every 12 or 18"

1.25" airspace

radiant barrier (perforated brown paper with aluminum foil facing on one
side, stapled to thel 1".25 thick blocks of wood 1" x 1" in size glued to
underside of plywood roof deck every 12 or 18", the blocks holding the
radiant barrier and fiberglass back from the underside of the roof deck by
1.25") stapled and siliconed to the small wood blocks

4" fiberglass or foamboard (undecided on which)
(may cut some leftover 24" wide 8 1/4" thick encapsulated fiberglass in half
using electric meat carving type knife and use the +/- 4" thick halves
between the 24" on center rafters)

hardie panel or soffit panels atached to 2x6 rafters as the ceiling

any ideas?





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HerHusband
 
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Effi,

thought of shimming the rafters down (making them thicker) but didn't
like the idea of heavy hardie panel ceiling attached to 2x4's attached
to 2x4's, so thought about running 2x6's alongside the existing 2x4's,


The biggest problem I see with that arrangement is the overall thickness of
the doubled up rafters. The wood framing is the weak link in the
insulation. In simple terms, the space taken up by the rafter is
uninsulated. If you double up the rafters, you'll have twice as much
uninsulated space (twice as much heat loss).

If you used construction adhesive and long screws every 12-16" or so to
attach the shim boards, I doubt you'll have any problems. I don't know what
a Hardie-panel weighs, but even if it weighs 100 pounds, that's only a bit
over 3 pounds for each square foot (4x8 sheet). With 24" OC rafter spacing,
you may end up with 7-8 pounds on each linear foot of the rafter. Not a big
load.

Alternatively, or in combination, you could glue/nail plywood on both sides
of the rafter and shim board. In effect, you would be building box
beams. This would actually allow you to increase the rafter depth as much
as you wanted. In fact, you could provide an air gap between the rafter and
shim board, which would reduce thermal bridging. You could even insulate
that gap if you want to get really efficient.

wood blocks 1" x 1" square x 1.25" thick glued to underside of plywood
roof decking staggered every 12 or 18"


Sounds like a lot of work with little gain. Increase the insulation space
and use standard plastic insulation baffles if you need them.

radiant barrier (perforated brown paper with aluminum foil facing on
one side, stapled to thel 1".25 thick blocks of wood


If you use a radiant barrier, it should be on the heated side of the
insulation, not against the roof. You want to reflect the heat back into
the room, before it goes into the insulation.

(unless you live in a warm climate and are more concerned about keeping the
heat OUT of the house).

may cut some leftover 24" wide 8 1/4" thick encapsulated fiberglass
in half using electric meat carving type knife


Sounds real itchy... Easier to just lay the mat over a board, compress it
with another board, and a quick swipe with a sharp knife. You'll end up
with a cleaner cut and less fiberglass dust floating in air. Be sure to
wear gloves and dust masks. Insulating is miserable work...

Anthony
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If you're going to modify the rafters anyway, just convert them
into the upper chord of a truss, using 2x3s as the lower chord,
and regular metal or plywood gussets. That will give you
all the joist-depth you can use. If you're converting a pre-existing
flat-ceiling into a cathedral, that means you're taking out the
existing ceiling joists and-or collar-ties, right? Have you
worked out what that's going to do to the tops of your walls,
in terms of resisting the outward thrust of the roof?

--Goedjn

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effi
 
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"HerHusband" wrote in message
...
Effi,

thought of shimming the rafters down (making them thicker) but didn't
like the idea of heavy hardie panel ceiling attached to 2x4's attached
to 2x4's, so thought about running 2x6's alongside the existing 2x4's,


The biggest problem I see with that arrangement is the overall thickness
of
the doubled up rafters. The wood framing is the weak link in the
insulation. In simple terms, the space taken up by the rafter is
uninsulated. If you double up the rafters, you'll have twice as much
uninsulated space (twice as much heat loss).

If you used construction adhesive and long screws every 12-16" or so to
attach the shim boards, I doubt you'll have any problems. I don't know
what
a Hardie-panel weighs, but even if it weighs 100 pounds, that's only a bit
over 3 pounds for each square foot (4x8 sheet). With 24" OC rafter
spacing,
you may end up with 7-8 pounds on each linear foot of the rafter. Not a
big
load.

Alternatively, or in combination, you could glue/nail plywood on both
sides
of the rafter and shim board. In effect, you would be building box
beams. This would actually allow you to increase the rafter depth as much
as you wanted. In fact, you could provide an air gap between the rafter
and
shim board, which would reduce thermal bridging. You could even insulate
that gap if you want to get really efficient.

wood blocks 1" x 1" square x 1.25" thick glued to underside of plywood
roof decking staggered every 12 or 18"


Sounds like a lot of work with little gain. Increase the insulation space
and use standard plastic insulation baffles if you need them.

radiant barrier (perforated brown paper with aluminum foil facing on
one side, stapled to thel 1".25 thick blocks of wood


If you use a radiant barrier, it should be on the heated side of the
insulation, not against the roof. You want to reflect the heat back into
the room, before it goes into the insulation.

(unless you live in a warm climate and are more concerned about keeping
the
heat OUT of the house).

may cut some leftover 24" wide 8 1/4" thick encapsulated fiberglass
in half using electric meat carving type knife


Sounds real itchy... Easier to just lay the mat over a board, compress it
with another board, and a quick swipe with a sharp knife. You'll end up
with a cleaner cut and less fiberglass dust floating in air. Be sure to
wear gloves and dust masks. Insulating is miserable work...

Anthony


plenty of food for thought here

also been looking at
http://www.owenscorning.com/around/i...sultoattic.asp
for ideas

am now considering following layers from underside of plywood roof decking
down:

layer 1.
Owens Corning Raft-R-Mate® attic vents attached to underside of plywood roof
decking
http://www.owenscorning.com/around/v...mate_attic.asp

layer 2.
radiant barrier; yes in warmer clime so installed closer to roof to keep
heat out; am considering leaving radiant barrier out, pending research on
effect on asphalt composition roof shingles and ridge vent installed on that
section of roof to vent any extra heat from radiant barrier

layer 3.
pieces of 2x4 about 5" in length, one end attached to the underside of the
roof rafter 2x4, making it 5" + 3.25" = 8.25 inches from the underside of
the plywood roof decking, one 5" piece attached every 3' or so along the
roof rafter, by means of glue and press on metal braces which overlay and
pierce both boards being joined

layer 4.
a secondary 2x4 running the length of the roof rafters and attached to the
5" 2x4 pieces mentioned in layer 1.; the secondary 2x4 will be attached to
the 5" pieces with the 4 side of the 2x4 running horizontal, making the
length from the underside of the plywood roof decking now 8.25" + 1.5"
(thickness of secondary 2x4 attached horizontally) = 9.75";
may need or want to add some stability 2x4s between each new "extended
rafter" if they sway due to new length from roof

layer 5.
4" of fiberglass insulation between new "extended rafters"

layer 6.
hardie panel ceiling attached to new "extended rafters"


seems this arrangement might work, 9.75" thick air space created and used
for:
1.50" or so foam attic vents
8.25" insulation (this way can use encapsulated 8.25" thick
fiberglass without modification)



as to other poster's question, ceiling joists will stay in place, could be
removed later




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HerHusband
 
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Effi,

www.owenscorning.com


Yep, I visited there a lot when we were preparing to insulate our house
too...

layer 1.
Owens Corning Raft-R-Mate® attic vents


Depending on how much depth you finally end up with, you may only need them
at each end of the rafter span where the insulation can get bunched up and
block off the air flow. But, you can certainly use them the full length of
the rafter bay if you wish. Just more cost (and slightly more restriction
to the airflow).

layer 2.
radiant barrier; yes in warmer clime


Sounds fine. I have no experience with radiant barriers.

layer 3.
one 5" piece attached every 3' or so along the roof rafter,
by means of glue and press on metal braces


I personally would not trust the press on metal braces. I know they use
them for roof trusses, but they have a big press in the factory to press
them in firmly and evenly. I don't see how you could ever achieve the same
results in the field.

If you want to use metal braces, I would get the types that have all the
little holes in them, then nail them up with joist hanger nails (short
lengths that won't go all the way through the 2x lumber).

I still think plywood supports would be cheaper and easier to install.

layer 4.
a secondary 2x4 running the length of the roof rafters
and attached to the 5" 2x4 pieces mentioned in layer 1.


I was just looking at an old article from the Journal of Light Construction
Online (couldn't find it online now) about "Energy efficient cathedral
ceilings". One of their techniques was to use 4" wide plywood gussets
nailed to the rafter with 8D nails and to the new bottom chord (2x3 in
their case). By adjusting the length of the gussets, they could adjust the
depth available for insulation. From what I could tell, they only nailed
the gussets on one side of the rafter.

If it were me, I would probably use wider gussets or even full length
strips of plywood, just for the added strength.

may need or want to add some stability 2x4s
between each new "extended rafter" if they sway


If each end is fastened securely, I wouldn't think there would be too much
sway (don't know how long your span is), but I see no real problem with
your solution.

9.75" thick air space created and used for:
1.50" or so foam attic vents
8.25" insulation


Around here, I would try for R30 minimum in the ceiling if at all possible.
But, you may not need that much in your climate. You would have to do some
checking on that.

In any case, your current plan sounds much better than your original
proposal.

Have fun!

Anthony
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If it were me, I would probably use wider gussets or even full length
strips of plywood, just for the added strength.


The thing is, you don't really NEED all that much strength. You're
only holding up the bottom chord, fiber insulation, and sheetrock,
That's something like 7 PSF dead-load. The only problems occur
in 6 years, when someone decides to hang a swing-chair from
the rafters with lag-bolts...



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effi
 
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"HerHusband" wrote in message
...
Effi,

www.owenscorning.com


Yep, I visited there a lot when we were preparing to insulate our house
too...

layer 1.
Owens Corning Raft-R-Mate® attic vents


Depending on how much depth you finally end up with, you may only need
them
at each end of the rafter span where the insulation can get bunched up and
block off the air flow. But, you can certainly use them the full length of
the rafter bay if you wish. Just more cost (and slightly more restriction
to the airflow).

layer 2.
radiant barrier; yes in warmer clime


Sounds fine. I have no experience with radiant barriers.

layer 3.
one 5" piece attached every 3' or so along the roof rafter,
by means of glue and press on metal braces


I personally would not trust the press on metal braces. I know they use
them for roof trusses, but they have a big press in the factory to press
them in firmly and evenly. I don't see how you could ever achieve the same
results in the field.

If you want to use metal braces, I would get the types that have all the
little holes in them, then nail them up with joist hanger nails (short
lengths that won't go all the way through the 2x lumber).

I still think plywood supports would be cheaper and easier to install.


i see now, and will use them, might even be stronger



layer 4.
a secondary 2x4 running the length of the roof rafters
and attached to the 5" 2x4 pieces mentioned in layer 1.


I was just looking at an old article from the Journal of Light
Construction
Online (couldn't find it online now) about "Energy efficient cathedral
ceilings". One of their techniques was to use 4" wide plywood gussets
nailed to the rafter with 8D nails and to the new bottom chord (2x3 in
their case). By adjusting the length of the gussets, they could adjust the
depth available for insulation. From what I could tell, they only nailed
the gussets on one side of the rafter.

If it were me, I would probably use wider gussets or even full length
strips of plywood, just for the added strength.



will use full length strips of plywood, good idea



may need or want to add some stability 2x4s
between each new "extended rafter" if they sway


If each end is fastened securely, I wouldn't think there would be too much
sway (don't know how long your span is), but I see no real problem with
your solution.

9.75" thick air space created and used for:
1.50" or so foam attic vents
8.25" insulation


Around here, I would try for R30 minimum in the ceiling if at all
possible.
But, you may not need that much in your climate. You would have to do some
checking on that.



for attic ceiling here
http://www.owenscorning.com/around/i...ion/rvalue.asp
or here
http://www.owenscorning.com/around/i...ue_results.asp
the DOE reccomends r-49 in the attic, for texas!, and the attic only had 4"
of glass (r-11 to r-15?) as originally built, a whole subdivision of houses
the same way ! ! !

sounds like the fed govt should give us all a tax credit for getting our
attic insulation up to what they specify since the houses were malequipped
with insulation when built and the home builders can probably no longer be
sued in a class action suit

then there's the cadmium problem with galvanized pipe, which the industry
has known about for years...

this source

says
"If you find cadmium in your hot or cold water, you will never be able to
filter it out. Nor should you switch to bottled water. The amount of cadmium
in your clothing from doing laundry with this water is already too much for
your adrenals and kidneys.
Change your galvanized pipes to PVC plastic. If you believe you already have
plastic pipes or all copper (which leads to leukemia, schizophrenia and
fertility problems) you will need to search every inch of plumbing for a
very short piece of galvanized pipe left in the system! A piece as short as
a 2 inch T or Y can be causing all the trouble."

modern life is so wonderful ; )



In any case, your current plan sounds much better than your original
proposal.



many thanks for the ideas

will post in the new year about results



Have fun!

Anthony



  #17   Report Post  
 
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Something ain't right here. You have a roof that uses 2X4's on 24"
centers for rafters? And you want to now turn it into a cathedral
ceiling by insulating it and sheetrocking it? I think the first thing
needed is some engineering calculation to figure out how the roof is
going to support the load or maybe even how it's even still there
before you do anything else to it.

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effi
 
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"effi" wrote in message
...
"HerHusband" wrote in message
...
Effi,

www.owenscorning.com


Yep, I visited there a lot when we were preparing to insulate our house
too...

layer 1.
Owens Corning Raft-R-Mate® attic vents


Depending on how much depth you finally end up with, you may only need
them
at each end of the rafter span where the insulation can get bunched up
and
block off the air flow. But, you can certainly use them the full length
of
the rafter bay if you wish. Just more cost (and slightly more restriction
to the airflow).

layer 2.
radiant barrier; yes in warmer clime


Sounds fine. I have no experience with radiant barriers.

layer 3.
one 5" piece attached every 3' or so along the roof rafter,
by means of glue and press on metal braces


I personally would not trust the press on metal braces. I know they use
them for roof trusses, but they have a big press in the factory to press
them in firmly and evenly. I don't see how you could ever achieve the
same
results in the field.

If you want to use metal braces, I would get the types that have all the
little holes in them, then nail them up with joist hanger nails (short
lengths that won't go all the way through the 2x lumber).

I still think plywood supports would be cheaper and easier to install.


i see now, and will use them, might even be stronger



layer 4.
a secondary 2x4 running the length of the roof rafters
and attached to the 5" 2x4 pieces mentioned in layer 1.


I was just looking at an old article from the Journal of Light
Construction
Online (couldn't find it online now) about "Energy efficient cathedral
ceilings". One of their techniques was to use 4" wide plywood gussets
nailed to the rafter with 8D nails and to the new bottom chord (2x3 in
their case). By adjusting the length of the gussets, they could adjust
the
depth available for insulation. From what I could tell, they only nailed
the gussets on one side of the rafter.

If it were me, I would probably use wider gussets or even full length
strips of plywood, just for the added strength.



will use full length strips of plywood, good idea



may need or want to add some stability 2x4s
between each new "extended rafter" if they sway


If each end is fastened securely, I wouldn't think there would be too
much
sway (don't know how long your span is), but I see no real problem with
your solution.

9.75" thick air space created and used for:
1.50" or so foam attic vents
8.25" insulation


Around here, I would try for R30 minimum in the ceiling if at all
possible.
But, you may not need that much in your climate. You would have to do
some
checking on that.



for attic ceiling here
http://www.owenscorning.com/around/i...ion/rvalue.asp
or here
http://www.owenscorning.com/around/i...ue_results.asp
the DOE reccomends r-49 in the attic, for texas!, and the attic only had
4" of glass (r-11 to r-15?) as originally built, a whole subdivision of
houses the same way ! ! !

sounds like the fed govt should give us all a tax credit for getting our
attic insulation up to what they specify since the houses were malequipped
with insulation when built and the home builders can probably no longer be
sued in a class action suit

then there's the cadmium problem with galvanized pipe, which the industry
has known about for years...

this source



forgot to add this link last time about the galvanized pipe problem
http://www.curezone.com/clark/high.asp


says
"If you find cadmium in your hot or cold water, you will never be able to
filter it out. Nor should you switch to bottled water. The amount of
cadmium in your clothing from doing laundry with this water is already too
much for your adrenals and kidneys.
Change your galvanized pipes to PVC plastic. If you believe you already
have plastic pipes or all copper (which leads to leukemia, schizophrenia
and fertility problems) you will need to search every inch of plumbing for
a very short piece of galvanized pipe left in the system! A piece as short
as a 2 inch T or Y can be causing all the trouble."

modern life is so wonderful ; )



In any case, your current plan sounds much better than your original
proposal.



many thanks for the ideas

will post in the new year about results



Have fun!

Anthony





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You don't eh? He's got a roof made of 2X4's on 24 inch centers.
That's sufficient for a light roof in a place where it doesn't snow
much and with a span of maybe 7 ft max. And that's assuming whoever
built it used only quality construction grade 2X4's, not some random
studs. Anyone taking that care likely would have used 2X6's to begin
with.

The previous advice to build out the rafters and correctly reinforce
them is the right advice. If done correctly, it will make it strong
and fix the insulation issue at the same time.

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