I have a single story ranch house that has brick veneer on 3 sides & 3/8″ T111 plywood panel on the back. I can’t stand the look of the T111.
Since the house was built in the mid 70’s, it was poorly insulated to begin with and there is minimal insulation in the walls. It has been my intention to remove the T111, put up polyiso 4×8 foam sheets covered with house wrap (Tyvek) and then install the final surface of Hardi Panel 4×8 sheets over the tyvek with a drainage plane/ rain screen (3/8- 1/2″) behind the Hardi panel. But I’m beginning to rethink that approach.
I live in a hot & humid area where snow doesn’t fall & stick & ice doesn’t form.
Two Questions:
1) Is it worth the time & expense to remove the T111 as I had originally planned and then insulate properly between the studs but then continue with the polyiso sheets & Tyvek to remove as many thermal breaks as possible? OR should I just leave the T111 in place to provide a where-ever-you-need-it nail base for the polyiso, Tyvek, & Hardi panel?
According to Charlie Wing’s Visual handbook, If I left the T111 in place & then blew cellulose in the cavity it would bring the wall up to R-12 or so and then covering it with 1″ of polyiso sheets would top the wall out at about R-19 or so. Because the T111 wall is the south facing wall (almost due south), I’m thinking that may be effective in knocking down some cooling costs in the summer.
Regarding the roof where the majority of heat comes from, it is being upgraded with new reflective shingles (& maybe more polyiso on the decking) & about 15 inches more of blown in attic insulation, which should bring it to R-40 or a little better.
2) Is there a down side to leaving the T111 up? Do I also need to put up another drainage plane to allow for moisture moving from the inside to the outside?
Thanks for any help,
Ken
Replies
Leave it
My first thought would be to leave th T-111 in place, mostly for strucural reasons - both wind bracing and a nail base.
Blown in cellulose would work well for additional insulation.
The only reason I would consider removing the T-111 would be if you were thinking of a spray foam for insulation.I would not consider it if you were just planning of fiberglass batt insulation.
Terry
Terry,
Thanks for the reply.
That's pretty much the conclusion I'm coming to also. It certainly makes more sense than removing the T111 just because I don't like the look of it. One of the contributing factors for my original removal thought was due to some warping of some of the T111 panels and not wanting that to show through on the new Hardi panel surface.
I'll just make it a point to run horizontal & diagonal strings across the vertical strips I'll be using to create the drainage plane stand off to make sure the surface will not be warped and shim where needed.
Thanks again for the reply!
Ken
I just looked at a 1971 house of similar construction. My verdict: Remove and completely redo the siding.
Here's why:
Even though this home had a good coat of paint, and in many areas the siding was free of damage, it had obvious ripples (or waves) and the seams projected outward.
This, I believe, is because T-111 has a definite 'design life,' and starts absorbing moisture from day 1. It's also likely that the panels were installed snug to each other, leaving no room for expansion.
Degraded as it is, I doubt it will hold nails very well. Likewise, a wavy base will result in a poor look to the new siding. While your siding might not look as bad as the example I saw, it's only a matter of time.
Depending on your area, it might be OK to install Hardie directly over house-wrap. Personally, I prefer the idea of an underlayment of some sort; note that Hardie also makes a product for thise - as well as eaves and soffits.
If you remove the T-111, it will be a lot easier to insulate from the outside, as the siding will hide any repairs. Remember to leave a gap between the sheets of underlayment. In humid areas, I'd consider sealing / back-priming any wood product.
You'll also have the opportunity to an receptacles, move plumbing, etc., while the walls are open.
Also, he doesn't have to Tyvec the polyiso... it's already a vapor barrier! He just needs to tape the seams properly.