Interesting idea from San Antonio house

[ThingOfBeauty]

I found the insulation concept from this article on an historic-esque restoration
http://www.mysanantonio.com/business/37024799.html
to be a head scratcher.
Anyone who's thought out the vapor profile(s) in southern houses care to weigh in? I don't think it would work here where it gets cold a lot, and it's hard to imagine that it's a great idea even in a warmer, drier place; but maybe they're on to something.

[Lawrence Taylor]

Does not give enough detail (visual or otherwise). How much spray foam? Why spray foam vs. something already flat? Why Tyvek?

They don't provide any data. Who evaluates the performance of this system?
Who warrenties this system?

I gotta scatch my head too.
But I am green as grass when it comes to cold weather issues.

[ThingOfBeauty]

You're right, the article isn't that clear, and from other things the reporter wrote it's obvious they don't understand building too well. Your other questions are spot on as well.
Let's assume for the purposes of discussion that they stapled Tyvek to the inside faces of the studs & plates, attempting to maintain a small space between the sheathing & Tyvek, then used open-cell foam to fill the balance of the cavity which would be around three inches of foam.
I just don't get it, to me why not just hose it all down with closed cell? The cavity for air movement isn't intrinsically bad, but there's no way to get water out of it except drying, any water that makes it in should drop to the plate and soak in, right? Sounds sketchy.

[Lawrence Taylor]

Back to the reporter,
Who/what market is this article for?
Typical home owners that typically have no background?
Handymen doing,,,,,handyman stuff?
Contractors that have to restore historic structures?
Industry specific manufacturers trying to solve product short commings?

Is it to strong to say that this article may be a little irresponsible ?

[frenchie]

Reminds me a bit of Bill's idea, on this thread:

http://forums.jlconline.com/forums/s...ad.php?t=45436

[Pete Engle]

The SA approach and Bill's post are pretty similar. Bill's use of XPS probably gives you a bit better vapor management, unless the SA house filled the rest of the cavity with closed cell foam. If they did that, vapor management would be similar.

The big problem with insulating the walls in any old house is what to do with the moisture that's getting through the siding? Contrary to Robert's post on that other thread, if the siding is a single layer of clapboard and if (IF) the siding is somewhat loose, the gaps in the siding will allow the cavity between the back of the siding and the face of the insulation to be vented well enough to pressure equalize. The studs act as the vertical furring, and the cracks and gaps in the siding act as the vents. Equalized rainscreens don't just have to have vents top & bottom, they can vents all along the screen as well.

However, the studs will absorb moisture and wick it laterally into the rest of the wall system. If there's enough moisture there, the studs will rot. But I tend to think that if there's enough moisture to rot the studs now, there would probably already be stud damage, because the new approach doesn't really change the exterior drying potential at all. Since cold weather walls dry to the outside, this approach may actually work better in a cold climate than a warm one. San Antonio is probably OK, because it's not all that humid. I would be very careful about trying this in Miami. Heck, I'd be careful about trying it anywhere.

It would be great if you could fashion pan flashings for the base of each stud bay that drained out behind the lowest course of siding. If there is a "kicker" at the lowest course, that might not be too difficult.

One interesting issue with this approach would be that the tighter you make the siding joints, the worse the system might perform.....

Certainly the best approach is still going to be taking off the siding andputting on a real WRB and drain screen. But with retrofits (and everything else), budget and other drivers often win out. This might be worth trying, but I'd try to find a way to check out the walls occasionally, especially in high-risk flashing areas.