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wewantutopia 08-25-2012 12:45 AM

layered polyiso
 
Hello,

I am just about finished residing my house (going on 2 years now...). Under the siding on top of the sheathing, I covered the exterior with 1.5" Thermax polyiso.

I'm now finding out I was 1 sheet short. I can't find it ANYWHERE now (within a reasonable distance). In fact I can't find any brand foil-faced in 1.5".

My question is, can I layer .5" and 1" John Mansville foil faced polyiso without any ill effect? What if I peel the foil off of one back and one front, would that be needed? The seams are all taped of course.

Thanks.

Gary in WA 08-25-2012 01:20 AM

That will work, long as you have the housewrap in there (preferably under the foam board), and the air gap or rainscreen with any wood siding; Fig. 24, page 46; http://www.buildingscience.com/docum...-climate-zones

Don't bother pulling any foil facing as the inside foil face (alone) next to the sheathing will vapor (barrier) seal the wall there, be sure no inside vapor barrier. Without a strapping air gap- the outside foil is nil- unless using vinyl siding; http://energyguild.hubpages.com/hub/...lp-Save-Energy

Pictures, we love pictures!

Gary

wewantutopia 08-25-2012 09:02 AM

Quote:

Originally Posted by GBR in WA (Post 995852)
That will work, long as you have the housewrap in there (preferably under the foam board), and the air gap or rainscreen with any wood siding; Fig. 24, page 46; http://www.buildingscience.com/docum...-climate-zones

Don't bother pulling any foil facing as the inside foil face (alone) next to the sheathing will vapor (barrier) seal the wall there, be sure no inside vapor barrier. Without a strapping air gap- the outside foil is nil- unless using vinyl siding; http://energyguild.hubpages.com/hub/...lp-Save-Energy

Pictures, we love pictures!

Gary

I was mainly worried about water getting trapped between the 2 sheets. I guess that, since polyiso can absorb water, it is good thing to leave the foil on to protect the boards.

I do have housewrap between the sheathing and the foam. On top of the foam I have a "rainscreen"; I'm doing vinyl. I don't trust the adhesive on the tape to last for 20+ years (the life of the siding). I didn't want to lose the radiant barrier properties by covering the foil so... I got 1200 sq. ft. of emergency blankets (http://en.wikipedia.org/wiki/Space_blanket) for $35 and used them; lapping them properly of course.

Most of our 100 year old house now has 3" polyiso in between the studs that was foamed on all 4 sides so I'm not too worried about vapor migration.

The 2x4 wall assemblies now are ~R30 with ~10 of that being an exterior thermal break. I'm pretty psyched!

This spring I also covered the foundation to below the slab with 1.5" XPS.

Here's some pix:

This house was a foreclosure that the previous owners tried to flip and ran out of $. The did some REALLY bad work. For example: The replaced the windows (except the basement, I did that) with "standard" sized windows. The resulting gaps were just covered with OSB and painted to match the asbestos siding.

Before:
https://lh4.googleusercontent.com/-_...s640/25800.JPG

https://lh3.googleusercontent.com/-f...0/100_2083.JPG

https://lh4.googleusercontent.com/-F...0/100_2108.JPG

Foundation Before:
https://lh5.googleusercontent.com/-8...s640/26695.JPG

After new windows, fixing the mortar joints, repairing some of the crumbling concrete, parging, and 6 coats of liquid rubber foundation coating:

https://lh3.googleusercontent.com/-Q...0/100_3292.jpg

Foamed:
https://lh6.googleusercontent.com/-3...0/100_3309.jpg

Finished. 6 More coats liquid rubber coating on the foam with sand added for texture:
https://lh4.googleusercontent.com/-g...0/100_3322.jpg

Here is the last wall. Part of this project includes all new electric service, replacing the original meter and wiring. The new location for the meter is to the right of the picture (out of view), but that is what the 2x6s are running along the roof to near the peak.

https://lh5.googleusercontent.com/-u...0/100_2471.JPG

https://lh6.googleusercontent.com/-_...0/100_3361.JPG

https://lh4.googleusercontent.com/-s...0/100_3394.JPG

Thanks for your help!!

Windows on Wash 08-26-2012 12:23 PM

Cool project.

Congrats to you for doing your research and doing it right.

wewantutopia 08-26-2012 07:29 PM

Hey thanks! It's a totally different house already, but there is still LOTS to do!

Windows on Wash 08-26-2012 11:30 PM

Quote:

Originally Posted by wewantutopia (Post 997064)
Hey thanks! It's a totally different house already, but there is still LOTS to do!

There always is.

Ed Harris doesn't talk about that in those BS home ownership ads does he....:whistling2:


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