Rigid Foam Insulation+Hardieplank Siding
I’d like to know how you can install foil-faced rigid foam insulation with Hardieplank lap siding.
I’ve installed Hardieplank siding without rigid foam with the layers being, from inside to out: Studs, OSB sheathing, Tyvek housewrap, (new construction) vinyl windows, Hardieplank lap siding.
If I was going to add rigid foam insulation, I’m not sure where it would best go in the layers. If it went directly on the studs, it would lessen the effectiveness of the sheathing. If it went on the sheathing, it seems it might intefere with the nailing of the siding (especially depending on how thick it is).
Is this something that is done? Exactly where and how would I install the the foam, what thickness would be advisable, and would it change the way the siding, sheathing or windows were mounted?
Thanks (I’m in San Diego, if that matters, and the main concern with the wall is its southern exposure and heat from the sun).
Replies
I think that to meet code requirements for shear in an earthquake zone you will have to put the foam on top of the OSB sheathing. Then strap it with 1x4 and nail the Hardieplank lap siding to the straping.
I think Hardie allows up to 1" ridgid foam under the siding.
Check ou thier web site. It is all there.
Hey JD i'm no expert but I want to say someone here said Hardi does not recommend using both foam and sheathing only one or the other. I could be wrong but that seems to ring a bell for some reason.
even if Hardie allows it, i wouldn't do it.
not after seeing an install done last year in this manner.
wavy wavy wavy with lots of gaps
had a little to do with the install.
but
it's just too hard to gauge the nail driving over the foam.
carpenter in transition
I haven't done it personally, but I have watched other builders put hardie lap over 1" foam, and when they are done, you can't tell the difference from a job done straight on sheathing.
We have installed cement siding over foam many times. I don't like to do it because it is a PITA, but we don't have any bad problems with it.
You have to use longer nails obviously and you will get the best results from drilling for the fastener at the butt joints if you don't have any OSB or plywood under the foam.
When done with some care, it's impossible to tell the foam is under the siding.