Insulating old house walls

JRMichler · 09-29-18, 07:17 PM

Foam on the outside is an excellent idea in an older house. A friend once put new siding on an older house. He took the advice of his neighbors who told him that foam was not necessary if he was careful installing tar paper. He was quite upset when the finished job leaked almost as bad as the original house.

I once added foam to the outside of an old house that was sheathed with some sort of fuzz board. The house was much more comfortable afterward, especially in the summer.

Foam on the outside becomes your vapor barrier. If you make it thick enough, the inside surface of the foam cannot condense, even if you fill the stud cavities with insulation.

A deluxe job would be 3" or 3.5" of foam, with 1/2" thick plywood/OSB on the outside for nailing the siding.

bpatton · 10-08-18, 08:30 AM

"I once added foam to the outside of an old house that was sheathed with some sort of fuzz board. The house was much more comfortable afterward, especially in the summer."

How did you do deal with the trimming around the windows and doors? That is where I'm stuck at right now. Planning on using Tyvek as an air barrier and taping all of the seams and flashing everything heavily then putting 2in poly-iso over the top of that, siding on top of that with furring strips. I was planning on the windows being installed in the plane with the existing wall sheathing instead of jacking them out to the (new) siding. But that leaves me trimming out the areas around the windows (on the outside) to try to cover up the foam.

JRMichler · 11-07-18, 06:36 PM

Quote:

Originally Posted by bpatton

How did you do deal with the trimming around the windows and doors? That is where I'm stuck at right now.

On that job, I used 1" foam. The windows had been installed such that I could just butt the foam up to them.

If I was doing a similar job today, I would use 3" to 4" of foam. I would remove the siding and windows, then install the new foam over a whole wall. Two layers of foam, tape all joints of each layer. Then 1/2" of OSB on top. Then I would go inside, cut out a window opening, then put in a casing out to the OSB. Install the rain screen (Tyvek or whatever), then install the window. Repeat until the entire wall is done, then install the siding. The windows would be flush with the outside.

That's similar to my present house, which was built with 3.5" stud walls and 4" of foam on the outside.

09-29-18, 07:17 PM	#1
JRMichler Apprentice EcoRenovator Join Date: Apr 2012 Location: Phillips, WI Posts: 109 Thanks: 10 Thanked 30 Times in 25 Posts	Foam on the outside is an excellent idea in an older house. A friend once put new siding on an older house. He took the advice of his neighbors who told him that foam was not necessary if he was careful installing tar paper. He was quite upset when the finished job leaked almost as bad as the original house. I once added foam to the outside of an old house that was sheathed with some sort of fuzz board. The house was much more comfortable afterward, especially in the summer. Foam on the outside becomes your vapor barrier. If you make it thick enough, the inside surface of the foam cannot condense, even if you fill the stud cavities with insulation. A deluxe job would be 3" or 3.5" of foam, with 1/2" thick plywood/OSB on the outside for nailing the siding.

10-08-18, 08:30 AM	#2
bpatton Lurking Renovator Join Date: Oct 2017 Location: Tampa, Fl Posts: 10 Thanks: 2 Thanked 1 Time in 1 Post	"I once added foam to the outside of an old house that was sheathed with some sort of fuzz board. The house was much more comfortable afterward, especially in the summer." How did you do deal with the trimming around the windows and doors? That is where I'm stuck at right now. Planning on using Tyvek as an air barrier and taping all of the seams and flashing everything heavily then putting 2in poly-iso over the top of that, siding on top of that with furring strips. I was planning on the windows being installed in the plane with the existing wall sheathing instead of jacking them out to the (new) siding. But that leaves me trimming out the areas around the windows (on the outside) to try to cover up the foam.