Rigid foam board insulation

Posted by LM on September 3, 2006, 10:00 pm

I'm replacing my siding and find lots of gaps in the fiberglass inulation
(in-wall). I am thinking of adding foam boards to the exterior walls to
better seal them and add little insulation. Going by R-value, this doesn't
add much (1/2" R4) but maybe this would protect better against winds etc. I
am installing hardie plank siding. Will this home 'breath' ?
ventilation? Anyone has experience with this type of insulation?

Luke

Posted by JimL on September 4, 2006, 1:00 am

> I'm replacing my siding and find lots of gaps in the fiberglass inulation
>(in-wall). I am thinking of adding foam boards to the exterior walls to
>better seal them and add little insulation. Going by R-value, this doesn't
>add much (1/2" R4) but maybe this would protect better against winds etc. I
>am installing hardie plank siding. Will this home 'breath' ?
>ventilation? Anyone has experience with this type of insulation?
>Luke

If you are replacing siding then don't even think about breathing
problems. I promise, you have lots of breating going on, even if you
wrap it twice.

Posted by m Ransley on September 4, 2006, 8:10 am

You won`t get R4 per 1/2" out of any board I know of, R7.2" new and
stabilised at R6+" is the best Polyisosyanurate gets. I covered my
house in 2" polyiso for R 14.4. Can you replace siding on a soft surface
and not over nail it making it uneven? I covered mine in Osb.

Posted by John McGaw on September 4, 2006, 10:07 am

m Ransley wrote:

> You won`t get R4 per 1/2" out of any board I know of, R7.2" new and
> stabilised at R6+" is the best Polyisosyanurate gets. I covered my
> house in 2" polyiso for R 14.4. Can you replace siding on a soft surface
> and not over nail it making it uneven? I covered mine in Osb.
>

1/2" Dow blue foam board is R3 and that is the best I could find when I
searched for materials for my basement remodel. Perhaps one of the
foil-faced types might do better but I don't recall any.

--
John McGaw
[Knoxville, TN, USA]
http://johnmcgaw.com

Posted by Eric in North TX on September 4, 2006, 10:19 am

I tried just about every brand a few years ago on a west wall I
rebuilt, the blue board won as somewhat effective, the foil covered
white crap is landfill. Only the blue board is only slightly more
effective than an empty space even when fitted with surgical precision.
A poorly fitted R-13 fiberglass did much better. I've ripped most of it
out and replaced it with R-16 fiberglass. The blue has its uses, and I
would use it again, it has the advantage of being softer and tighter so
accurate cuts can be made with out the shattering and crumbling the
white stuff does. Any place the bats will fit, isn't one of its uses.

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