I am insulating my house in North Carolina seven miles from the ocean. The house was built in 1935. It has pine lap siding directly over the studs two foot on center, no sheating or vapor barriers. I am planning on removing the drywall and installing 1″ foam in between the stud bays, then installing 3/4″ foam horizontallly over the interior face of the studs, followed by 3/4″ nailers, and drywall. I’m hopeing that any water that gets past the siding will be able to evaporate in the 2 1/2″ space between the back side of the foam board and inside of siding. Do you think I need a vapor barrier behind the drywallk?
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Are there any spray foam installers in your area?
If your removing the drywall anyway, a complete fill of the stud bay will leave you much better off.
There are none in my area. Spray foam is also cost ineffective, although I know it is a superior product and also provides an excellent air barrier. I'm trying to get the air barrior effectiveness and settle for less r value. I am worried about vapor barrier (felt paper or plastic) trapping moisture in between drywall and foam? Thanks, greek
Where are you putting the first piece of foam? Is it going tight to the back of the outside wall or someplace closer to the center? How will it be cut? Fastened? What kind of foam are you using?
Then you are going to put a second piece of foam on the inside and essentiallly trap any moisture between them?
Doesn't sound like a good system.
You are near the ocean. Probably going to get some storms. Old siding likely is not tight and moisture will get in. I think I would do it differently, probably reside it with insulation on the outside of the studs, under the siding. It's going to be a PITA no matter how you do it.
How big is the house? Ranch or 2 story or...
Don K.
EJG Homes Renovation - New Construction - Rentals
I was considering installing 1" pink board up to the interior face of studs, cut and caulked in between the wall studs, then installing 3/4" over the face of the interior studs for a thermal break, then installing nailers and drywall. Effectively, a rain screen on the inside. The house is one story on crawl. I can't open up the outside of the house. I don't want to mess with the original pine lap siding, in great shape because it was covered with asbestos shake.
I have a feeling that if you do this, you are going to change the dynamics of the house. [I know - that's what you want. To keep the outside air out. :-) ] That siding has been there a long time. If you suddenly back it up with the insulation, the inside and outside faces of the boards may react to the differential change in humidity and you may get some lifting, cupping, etc., not to mention paint problems on the outside.
If you do go forward with it, I suggest that you make sure the back of the siding is primed/painted with the same thing as the outside. That alone can make a difference in how the siding performs. I would also detail something at the bottom to get any incoming water out rather than let it sit on the sill plate. This goes for both the area between the 2 pieces of insulation and also at the bottom of the outer piece. This could mean removal of the bottom piece of siding to put some kind of pitched pan in there.
Good luck.
Don K.
EJG Homes Renovations - New Construction - Rentals