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15 Answers

I am planning the second floor of a new build home in climate zone 4 which i am completing in stages due to money constraints. The building envelope is hot roofed with 4" cc spray foam on the roof deck and 5.5" of rock wool beneath that, the walls are 2x4 with cavity insulation and 2" of XPS on the outside of the wall sheathing. The walls are further air sealed with a combination of Knauf eco-seal and cc spray foam and the basement walls have 2" of cc spray foam so the envelope is reasonably tight. Fuel source available is propane which is already piped into the home.

Asked By jack ostrick | Jan 4 13
3 Answers

First, this is for residences in Climate zone 5. We have seen several insulation companies recommend a flash and batt system to insulate a roof system in an unfinished attic space. The recommendation is for 3" of CC foam (R-20 to R-23) covered by an R-21 unfaced fiberglass batt for a total nominal R value of ~ R-40. The fiberglass batt is visible from the unfinished attic and according to the insulation company meets the dual role of an ignition barrier and an R-21 thermal break .

Asked By Jeffrey Rhodin | Dec 27 12
4 Answers

I understand the importance of super insulating the underside of a slab with large amounts of XPS foam, especially in my very cold climate (northern Maine). I have run across a unique foundation design of a passive house in Falmouth, MA, by architect Steven Baczek ( It involves insulating ABOVE the slab, essentially leaving the slab out of the conditioned space. His design involves 4" of XPS rigid foam resting on top of the slab, followed by 2x8 16" OC boards spanning the slab, resting on a 2x4 strut. 3/4" T+G subfloor covers the 2x8s.

Asked By Matthew Michaud | Dec 30 12

A few months ago I had my home insulated with closed cell foam. Now it's time to test it.

A good friend did a blower door test and took thermal photographs. It's a pretty good insulation job. There are places where the foam failed, but not many.

1) the framers created corner cavities "to hang drywall" (haven't they heard of clips?) that the insulators couldn't get to. I want to drill a hole a the top of the void and pump something in there to seal it up. What products can I use?

Asked By Judd Maltin | Dec 30 12
10 Answers

After many months of research (thanks to this site) I finally hired an insulation contractor for my attic. The contractor was certified by building performance institute and after 4 different estimates I was pretty confident I had selected the correct one.

Asked By Rocky Pembroke | Dec 22 12
6 Answers

I have a 100+ year-old home in climate zone 6A (Wisconsin) that needs new sheathing and siding, so I figured I may as well reinsulate the wall cavity as I pull and replace the sheathing (currently has R13 batt in a 2x4 wall cavity). After considering a variety of options, I keep coming back to flash and batt and wonder if this will work for me. Most (all?) flash and batt applications are applied from the interior--that is, 1-2" of closed-cell spray foam is applied to the exterior sheathing, batt insulation is installed, and drywall is put up.

Asked By Eric Rinehardt | Jul 27 12
14 Answers

My husband and I are building on our own a small house that we've tried to make as green as possible. Neither of us are familiar with green building (he's conventional framer) and we rely on this website and green building books to answer our questions. The one thing I'm stuck on is, do we need to have an HRV or ERV system? We are building the house as tight as possible, sealing all leaks, and have an inch of rigid foam on the exterior and will have R-21 cellulose interior insulation. The house is 24x24, two floors and an unfinished basement.

Asked By Morgan Clark | Nov 27 12
9 Answers

I've put insulation between my joists, and just was told, I put them in upside down. Apparently, the paper should face the floor above.
Would just slicing the paper suffice or should it all be turned around.


Asked By Deb Malloy | Nov 26 12
8 Answers

This question stems from a different conversation on here and we need some more help.

We're in Zone 5A. Our exterior has plywood, tar paper, 1" of foil-faced polyiso foam, and red cedar shake. The framing is 2x6 wood construction.

The interior will be heated with wood stoves only. We know to never have 2 vapor barriers. What we're wondering is if we need an additional vapor retarder on the interior? If so, what sort of barrier do we need? (Spray foam is prohibitively expensive).

Asked By user-1044776 | Dec 3 12
5 Answers

Does anyone see any potential problems using ZIP System's new R-Sheathing? The product comes in either 1/2" or 1" polyiso on the back of the sheathing between the sheathing and the studs.

Once again I am trying to figure out less costly ways to combat thermal bridging, create an air seal, and provide a rainscreen. I would be using the product with no interior vapor barrier therefore reducing the possibility for trapping moisture in the wall cavity.

Asked By Jason Macdonald | Aug 1 12
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