Hi,

Just received a quote for roof insulation with closed cell foam between
the rafters. The quote is for 3" and I am being told that 3" is 90% as
good as 6". Do I believe them?

Thanks,
Aaron

On 2009-08-20, Aaron Fude wrote:

Just received a quote for roof insulation with closed cell foam between
the rafters. The quote is for 3" and I am being told that 3" is 90% as
good as 6". Do I believe them?

That kind of stuff makes me paranoid. Foam just seems way too flammable a
material to entombing your home with.

On Aug 20, 10:05*am, Aaron Fude wrote:
Hi,

Just received a quote for roof insulation with closed cell foam between
the rafters. The quote is for 3" and I am being told that 3" is 90% as
good as 6". Do I believe them?

Thanks,
Aaron

I had a roofer tell me 1" of his foam equaled R 35, the dam liar. From
what I have read your foams go from aproximatly R 5 - R 7 per inch,
and thats it. Polyurethane is about R7" and other types less so going
by factual R values 3" is R15 to R21 depending on type of foam used,
ask them whose product they use and check that companies site, but no
foam is 90% different and R 21 isnt squat for insulation what I live
in Zone 5. Your bidder is lying to you.

On 2009-08-20, Aaron Fude wrote:

Just received a quote for roof insulation with closed cell foam
between the rafters. The quote is for 3" and I am being told that 3"
is 90% as good as 6". Do I believe them?

Are you insulating between the rafters because you'll be turning the
attic into habitable space?

As to your question, 6" of foam will be about twice as good an
insulator as 3" of foam. If your concern is about reducing the
heating and cooling costs of the entire house, then the useful of the
extra 3" of foam depends on how well everything else is insulated.

Here's a simplistic example: suppose the roof represents 20% of the
surface area of the house, and lets call F-1 the insulation value of
1" of foam. If the rest of the house is a perfect insulator
(impossible), doubling the roof insulation will halve the energy loss.
If the rest of the house is insulated to F-6, then the F-6 roof will
reduce the system energy loss by 17% over the F-3 roof. If the rest
of the house is insulated to F-3, then the reduction is only 10%. And
if the rest of the house is F-1, the reduction is only 4%.

Cheers, Wayne

"Aaron Fude" wrote in message
...

Just received a quote for roof insulation with closed cell foam between
the rafters. The quote is for 3" and I am being told that 3" is 90% as
good as 6". Do I believe them?

American taxpayers fund a government housing standards
laboratory precisely to answer questions like this (probably
free to householders.)

--
Don Phillipson
Carlsbad Springs
(Ottawa, Canada)

Wayne Whitney wrote:
On 2009-08-20, Aaron Fude wrote:

Just received a quote for roof insulation with closed cell foam
between the rafters. The quote is for 3" and I am being told that 3"
is 90% as good as 6". Do I believe them?

Are you insulating between the rafters because you'll be turning the
attic into habitable space?

As to your question, 6" of foam will be about twice as good an
insulator as 3" of foam. If your concern is about reducing the
heating and cooling costs of the entire house, then the useful of the
extra 3" of foam depends on how well everything else is insulated.

Don't think so. Resulting efficiency rate drops off as thickness increases.
If you're at 50% with 3", you might be at 70% with 6" and 80% at 9" and 85%
at 12" (numbers are made up).

You're spot on about insulating the rest of the house. It won't do much good
to insulate the attic if you leave the front door open.

On Thu, 20 Aug 2009 15:16:18 -0500, "HeyBub"
wrote:

Wayne Whitney wrote:
On 2009-08-20, Aaron Fude wrote:

Just received a quote for roof insulation with closed cell foam
between the rafters. The quote is for 3" and I am being told that 3"
is 90% as good as 6". Do I believe them?

Are you insulating between the rafters because you'll be turning the
attic into habitable space?

As to your question, 6" of foam will be about twice as good an
insulator as 3" of foam. If your concern is about reducing the
heating and cooling costs of the entire house, then the useful of the
extra 3" of foam depends on how well everything else is insulated.

Don't think so. Resulting efficiency rate drops off as thickness increases.
If you're at 50% with 3", you might be at 70% with 6" and 80% at 9" and 85%
at 12" (numbers are made up).

You're spot on about insulating the rest of the house. It won't do much good
to insulate the attic if you leave the front door open.


Although that is very true, it's also true that more heat escapes
upwards than outward. Overhead insulation tends to be the most
important. Better to have r50 in the attic and r20 in the walls than
the other way around.

Wayne Whitney wrote:
On 2009-08-20, Aaron Fude wrote:

Just received a quote for roof insulation with closed cell foam
between the rafters. The quote is for 3" and I am being told that 3"
is 90% as good as 6". Do I believe them?

Are you insulating between the rafters because you'll be turning the
attic into habitable space?

As to your question, 6" of foam will be about twice as good an
insulator as 3" of foam. If your concern is about reducing the
heating and cooling costs of the entire house, then the useful of the
extra 3" of foam depends on how well everything else is insulated.

Here's a simplistic example: suppose the roof represents 20% of the
surface area of the house, and lets call F-1 the insulation value of
1" of foam. If the rest of the house is a perfect insulator
(impossible), doubling the roof insulation will halve the energy loss.
If the rest of the house is insulated to F-6, then the F-6 roof will
reduce the system energy loss by 17% over the F-3 roof. If the rest
of the house is insulated to F-3, then the reduction is only 10%. And
if the rest of the house is F-1, the reduction is only 4%.

But, the energy saved by adding attic insulation is the same, regardless of the
other insulation in the house.

wrote:

Don't think so. Resulting efficiency rate drops off as thickness
increases. If you're at 50% with 3", you might be at 70% with 6" and
80% at 9" and 85% at 12" (numbers are made up).

You're spot on about insulating the rest of the house. It won't do
much good to insulate the attic if you leave the front door open.


I agree with Bub on this one. It is like SPF numbers on sunscreen.
Pretty soon you reach the point of diminishing returns.

Attic insulation is really a winter thing more than a summer thing
anyway. At a certain point you have to decide heat rises. You cold air
loss is down on the walls, windows and doors. Cooling your attic with
better ventilation may return more than an extra few inches of
insulation.

That depends. There are places where winter temperatures never drop below
50°F but summer temps can reach 130°F.

I'm in Houston and I'm blessed that I've actually seen snow. Not many of my
neighbors have.

"ShadowTek" wrote in message
. ..
On 2009-08-20, Aaron Fude wrote:

Just received a quote for roof insulation with closed cell foam between
the rafters. The quote is for 3" and I am being told that 3" is 90% as
good as 6". Do I believe them?

That kind of stuff makes me paranoid. Foam just seems way too flammable a
material to entombing your home with.


Foam is treated to make it self extinguishing. It will not burn unless
something next to it is burning. Code requires it to be covered with
sheetrock if exposed to the living space.

Aaron Fude wrote:
Hi,

Just received a quote for roof insulation with closed cell foam between
the rafters. The quote is for 3" and I am being told that 3" is 90% as
good as 6". Do I believe them?

Thanks,
Aaron
Hi,
Where do you live? What is your area building code?
I have R60 attic, R24 ext. walls, R12 basement walls
insulation. Roof is ceramic coated steel tiles.
Hottest summer temp. 33 deg. C. Coldest winter -37 deg. C.
Wind chill could go down to -50 deg. C but not very often.
We have Chinook frequently.
Very dry climate year round.

On Aug 20, 3:16*pm, "HeyBub" wrote:
Wayne Whitney wrote:
On 2009-08-20, Aaron Fude wrote:

Just received a quote for roof insulation with closed cell foam
between the rafters. The quote is for 3" and I am being told that 3"
is 90% as good as 6". Do I believe them?

Are you insulating between the rafters because you'll be turning the
attic into habitable space?

As to your question, 6" of foam will be about twice as good an
insulator as 3" of foam. *If your concern is about reducing the
heating and cooling costs of the entire house, then the useful of the
extra 3" of foam depends on how well everything else is insulated.

Don't think so. Resulting efficiency rate drops off as thickness increases.
If you're at 50% with 3", you might be at 70% with 6" and 80% at 9" and 85%
at 12" (numbers are made up).

You're spot on about insulating the rest of the house. It won't do much good
to insulate the attic if you leave the front door open.

It depends on where you live, his 3" of foam could be R15-R21, mimimal
code for my zone 5 area is R 35 and optimal is R60. Heat rises and in
cold areas you do see a difference in even room comfort going to R 60.
If he is in a cold winter area 3" of foam for a roof-attic is a joke
in my area where it was -20f last year. Sure you get diminishing
returns but I was paying near 120 a month gas where a neighbor with
same size house that had crap windows and near no insulation paid near
700 one month for gas, up north here it is better to overdo efficency,
so you dont overpay utilities for the rest of your life. It also
increases resale value alot, or can make the sale in tough times.

I would not.

--
Christopher A. Young
Learn more about Jesus
www.lds.org
..


"Aaron Fude" wrote in message
...
Hi,

Just received a quote for roof insulation with closed cell
foam between
the rafters. The quote is for 3" and I am being told that 3"
is 90% as
good as 6". Do I believe them?

Thanks,
Aaron

On 2009-08-20, HeyBub wrote:

Don't think so. Resulting efficiency rate drops off as thickness
increases. If you're at 50% with 3", you might be at 70% with 6"
and 80% at 9" and 85% at 12" (numbers are made up).

I'm not sure what kind of efficiency you are talking about. If the
R-value of 3" of foam is R-15, then the R-value of 6" of foam is about
R-30.

Cheers, Wayne

On 2009-08-20, Bob F wrote:

Wayne Whitney wrote:

Here's a simplistic example: suppose the roof represents 20% of the
surface area of the house, and lets call F-1 the insulation value
of 1" of foam. If the rest of the house is a perfect insulator
(impossible), doubling the roof insulation will halve the energy
loss. If the rest of the house is insulated to F-6, then the F-6
roof will reduce the system energy loss by 17% over the F-3 roof.
If the rest of the house is insulated to F-3, then the reduction is
only 10%. And if the rest of the house is F-1, the reduction is
only 4%.

But, the energy saved by adding attic insulation is the same,
regardless of the other insulation in the house.

I guess my main point was that you may be better off directing your
dollars towards insulating elsewhere in the house.

As to your comment, it is mostly true. Adding attic insulation may
change the mechanism of heat loss that the house experiences. So you
need to know something about the other insulation in the house to
figure out the impact of your added attic insulation.

Cheers, Wayne