I plan to re-side my 100 yr old home with hardi-plank. New window trim, corner boards, etc. I would like to add some type of insulation to the exterior before putting up the new siding. What is the best way to go here?
Dave
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I assume you don't mean blowing in the stud cavities? Unless your stud bays are already insulated, that's what I would suggest rather than adding insulation under the siding, since anything you put under the siding will have only minimal R value (R-2.5 or so per inch thickness of foam) in relation to the cost/hassle of installing it. Also, you may get yourself into an exterior vapor barrier problem if you use foam, so be careful. Also, you need to be careful nailing Hardi over foam -- it gives more than wood so you'll have to be a bit more careful not to overdrive the nails. Oh yeah, skip the Hardi for the corners and trim. Use Azek. Hardi's trim is so brittle, it's a pain to handle and install.
Mike Hennessy
Pittsburgh, PA
2.5 per inch? Maybe the half-inch... depending on the foam (XPS, EPS, Polyso), an inch of foam has an R-values of 5 to 7 per inch.
I agree with you overall, though - it's a huge hassle to install anything over 1/2 inch, lots of detailing / trim / flashing issues.
Doh! R-2.5 per inch was stoopid math mistake. I was figguring R-7.5 for 1-1/2" and muffed the calc which, you're right, makes it R-5 per inch. Still, not much benefit for the grief, especially if the stud cavities are empty, just waitin' for celulose.
Mike HennessyPittsburgh, PA
Too true, too true. Not argueing with that part.