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-   -   Exterior Foam sheathing thickness? (http://www.diychatroom.com/f19/exterior-foam-sheathing-thickness-32764/)

teachtech 11-28-2008 01:30 PM

Exterior Foam sheathing thickness?
 
I am about to install foam board ont the exterior of my home. The house has r-13 insulation and 1/"plywood sheathing. Will it make a big difference if I was to use 1" thick foam board instead of 1/2" foam board, the price difference is $7.00 and more of a hassle to install. My home is drafty and their or other issues such as the windows that are leaking. What do you think?? Thank You!

buletbob 11-28-2008 02:03 PM

Buy going with a thicker insulation board there are some issues you will have to deal with when you go to install your siding, some thing to consider.
1) you will have to pack out you window trim. I don't like my siding J channel sticking past my doors or windows I like to keep it back some.
2) what are you going to do with your gable trim, same thing you will have to caulk your Chanel to the rake trim to keep water from getting behind it.
This is why the 3/8" foam board is so popular, but the R- value is low. The 1/2" foam is what I normally use because of the R-3.2 rating you should Get around an R-6 or 7 with the 1" but you run into the above draw backs.
if your thinking of doing your roof do that first this way you can pack out your trim to accept the thickness of your insulation and siding, I like to have the foam and the siding behind the rake trim when I do the complete exterior of the house.if your going to change the windows you can then install a wooden build-out around the window openings the thickness of your foam then you can install siding. This is the sequence that I conform to. But read on you will get other great advice from the other pro,s on this site.
Good luck BOB.

teachtech 11-28-2008 07:13 PM

If you do not take into account of all the technical problems of installing thicker foam do you think the extra thickness will make a difference. I get the feeling a lot of heat is lost through the cieling into the attic. This is a ranch house and the attic has about 8" of blown in insulation. Thank You

Wildie 11-28-2008 08:30 PM

In my area, 1" of foam is standard, along with 2X6 wall studs filled with R20 insulation.
Ceiling insulation is R40 now, although my 60 year old house only has R30.
Lots of insulation saves heat in the winter and A/C costs in the summer!

buletbob 11-29-2008 05:36 AM

Quote:

Originally Posted by teachtech (Post 191213)
If you do not take into account of all the technical problems of installing thicker foam do you think the extra thickness will make a difference. I get the feeling a lot of heat is lost through the cieling into the attic. This is a ranch house and the attic has about 8" of blown in insulation. Thank You


I do not know what the R rating would be for 8" of blown insulation I know R-30 is around 9-1/4"
you think your losing it through the attic? let me ask ! when it snows and it covers your roof does it melt before the other surrounding houses?
is the whole attic covered with the insulation, It wasn't pulled back in spots was it?? BOB


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