Replace existing Siding and add Foam Board Insulation
retired7111
| Posted in Energy, Heating & Insulation on
I recently purchased a 1986 modular home in Frisco, North Carolina. The house has the original T1-11 sheathing that is beginning to deteriorate, with 3.5″ of fiberglass insulation. The inside finished walls are paneling that we are priming and painting. I want to remove the existing exterior siding and install 1″ of foam sheathing, cover that with 1/2″ Zip sheathing and then install new windows and the new siding, cement board shingles with SS nails. Am I missing anything? Thank you.
I should have added that under the T1-11 there is a layer of felt paper and 1/2″ plywood to keep the building from racking.
Replies
I wouldn't remove the siding. That stuff is probably glued and nailed down. UGGH...
I would put felt on it and nail on the hardi planks.
While the sideing may be deteriorating as an exterior surface, it's probably still doing well as a diaphram sheathing.
I think you should leave it in place, and use 2" rigid foam on the exterior. This will act as the air and vapor barrier as long as you seal and tape the seams, so you don't need felt or building paper like Tyvek/Typar. Attache vertical furring with coravent insect screens at the top and bottom as a rain screen vented channel behind your cement shingles.
That sounds like a lot of work for a relatively mild climate. I don't believe the foam would pay off. Frisco NC is on the outer banks.
Also there is the possibility of hurricanes, so the siding would have to be solidly attached. Foam board may add to the difficulty.
Yeah, I'd question the need to remove the T1-11 and would also question the merits of installing foam for your climate. Replace any rotten sections, of course, then install a housewrap and rainscreen (separately or as a single combo product), then durable siding such as cement, solid wood, or one of the newer composites.
Potentially you might be missing something
Why did it deteriorate-moisture-grade too high-other?
Correct that as part of your plan.
As far as windows and doors, get the specs b/4hand so if you need to change the openings, you'll not have to screw with your work. Properly flash those windows-you still using house wrap? What's the detail with zipsheathing and window install?
Vented soffit?
External wiring or light changes?
Bath or dryer exhaust change?
Exterior faucets?
Exterior foam over T-111
Retired 7111,
I agree with the other posters that the T-111 siding is best left in place. Install housewrap, followed by rigid foam insulation, followed by a rainscreen product like Cedar Breather, and then your new shingles. Be sure to get your flashing and water-management details right. For more information, see http://www.greenbuildingadvisor.com/blogs/dept/musings/how-install-rigid-foam-sheathing
I was about to question your use of housewrap along with foam, then I followed your link and learned about potential shrinkage. I had never known about that before!