Spray foam insulation without sheathing

[damiani]

I'm renovating a 100-year-old house, removing plaster and lath on all the walls, and I've been considering various options for wall insulation. It seems like spray foam has some great benefits over fiberglass--sound deadening, for instance, and the lack of need for a vapor barrier--but my house has wood clapboards on the exterior which are attached to the studs directly without any sheathing underneath. Is spray foam an option for me? Would it either (a) seep through the small gaps underneath each siding board, or (b) put too much pressure on them as it expands to that it will push them away from the studs?

Thanks for any insight...

[Cole]

I personally have never done it without some type of plywood or decking behind the siding.

Now since I said that, here goes.
The bad thing about going with spray foam insulation is that you and me dont know what will happen, it might leak through it might not. I can tell you if it does leak through you will have a bigger problem on your hands then you did originally.

[giddonah]

I've only done interior walls on my "antique". I got nothing for you. I can bring up the idea of stapling a vapor barrier up first, then spraying. That would keep the foam from seeping through the cracks.

[damiani]

I can bring up the idea of stapling a vapor barrier up first, then spraying.
I had considered that too, though I wonder about moisture collecting between the vapor barrier and the wood plank siding, and rotting the siding or dripping down and rotting the sill.

[giddonah]

Unless you have some incredible wood siding that's water-tight, any water you get between them will dry out. What will be there to keep the water there long enough to cause rot? I can't imagine clapboard siding retaining that much water by itself. I say it's a non-issue.






Oh, and if it does rot the siding, I was never here :wink: :lol:

[Cole]

Oh, and if it does rot the siding, I was never here :wink: :lol:

Yes he was, I just saved the web page. :P :P

[danh]

It is my understanding that you should never arbitrarily install a vapor barrier unless it is absolutely necessary. Virginia is entirely in ICC zone 4, which means that VDRs should only be on the inside (warm in winter side) of the wall assembly. While it is possible to build a wall with an exterior VDR in your climate, it's very tricky to get it to work.

Alternatively, why not use a permeable (breathable) housewrap type material, sealed with mastic at the studs? It keeps the insulation dry, and it will not contribute to condensation problems.