Low E House wrap
user-1093260
| Posted in Energy Efficiency and Durability on
Has anyone had any experience with Low E House wrap. Due to the existing design of this new home I am looking for the least expensive way to minimize thermal bridging. I am building with ICF foundation, 2×6 exterior studs, spray foam insulation, 1/2 plywood sheathing, cement board siding. At this stage of the game I can not afford to have this home re engineered. Looking for as efficient as I can get.
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Replies
Dana,
There is no legal definition of "low-e," I'm afraid. What is the emissivity of the housewrap?
The housewrap may or may not be a radiant barrier. One product that is touted as a low-e housewrap is Tyvek Thermawrap. Thermawrap is NOT a radiant barrier, since a radiant barrier must have an emissivity of 0.1 or less. The emissivity of Thermawrap is 0.2 -- too high to be considered a radiant barrier.
Products like Thermawrap only work if they are facing an air space, so that requires vertical rainscreen strapping between the Thermawrap and your siding. If you install the product this way, you will raise the R-value of the air space from R-1 (which you would get with any old housewrap) to R-2. In other words, the Thermawrap gives you an additional R-1. That's not much.
Or as another option, you may want to save money on the cavity spray foam, replace it with cellulose and install taped rigid foam outside the sheathing; it’ll replace the wrap as a WRB, and it will void the thermal bridging. You’ll have a more durable and better assembly, and more than likely, save you money.
I agree not to use spray foam or OSB for sheathing. The spray foam will stabilize in about one hour but your framing is drying and shrinking for 2 years after which time your "tight" home will now be very leaky. Cellulose is the way to go with exterior taped rigid foam and a poly interior air-vapor barrier. Like the post above, this will save you construction costs AND energy costs in the future AND make your home more comfortable.
Good advice from Stephen & Armando. SPF is not your best choice.
ditto
No location posted. In an A/C climate, no poly, need drying to the interior.