Thermal break strips?
Rather than add a layer of foam to the outside of a house or build a double stud wall, can I staple strips of fan-fold XPS (3/8 in.) to the inside and/or outside of studs to break the thermal bridge?
I understand that it’s not as good as sheets of 1 in. board, but it’s a lot cheaper than wrapping the outside with foam or buying twice as many studs.
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I would like to know if anyone has attempted this..and if they encountered any problems...I ran this idea up the flagpole at breaktime a couple of years ago ..consensus then was that it might cause waviness in the siding.
I just saw a magazine ad for a product just for this application. I think the material was peel and stick. However the product was intended for install on interior before drywall.
If you/re planning to put the foam strips over your sheathing at stud locations before the siding application I'm not too sure you'll get much benefit. The drywall will be warmed on the inside and transfer heat into and trough the studs to the sheathing - then the heat will be transfered into the space between sheathing and siding caused by the foam strips. I think you really need the strips either between drywall and studs and/or studs and sheathing.
I would be cautious about putting foam between studs and exterior sheathing.
It may compromise the shear strength of the sheathing...(may not meet code)
The advantage I see for foam strips outboard of the sheathing with siding is that it's a two-fer...you minimize thermal bridging and you get a furring strip for the rainscreen.
I am glad that you are considering heat transfer as a 3 dimensional property.
Heat does transfer sideways also...perhaps the strips should be 3 inches wide.
I am still a little concerned about waviness in the siding if the foam is crushed.
I believe that Joe Lstiburek actually tried this concept on some Habitat homes..but I do not know what the outcome was.
The strips under the drywall sounds interesting..I am curiuos if it would cause any installation or stability problems with the drywall...
One of the things exterior foam accomplishes is raising the temperature of the inside of the sheathing above the dew point. This prevents moisture problems like rot and mold.
Here in earthquake country you may not have foam between the stud and sheathing on the shear walls.
I think you are being penny wise, pound foolish. The house will stand for many years and the proven energy savings of exterior foam system will more than pay for any additional financing you will incur.
Good points Kurt...
Where do you build? What kind of claddings do you use with the foam?
Are you using any siding over foam? how about siding with foam and rainscreen furring strips? JB
I can't see any reason not to fur the inside of your wall frame with some sort of thermal-break material. This would conform closely to established industry practices (drywall nailers routinely install RC or other sorts of stripping under their GWB) and capture real efficiencies and economies. I think you'd want to keep an eye on the density/compressive strength of your furring (2# XPS should be fine) and make sure that your pattern provides truly continuous backing for the GWB. If you run adequate quality control on that furring installation, I think you'll find additional air-sealing benefit as the foam acts to gasket the GWB to the wall frame. (A lot more air passes laterally through our walls than most of us are aware of. You could also have your insulators foam-seal horizontal penetrations as well as vertical.) Let us know how it goes.