How to Install Insulation Under Siding
LESLIE: John in California is calling in with an insulation and a siding question. How can we help with the project?
JOHN: Well, I want to re-side the south side of my house and it currently has 5/8 T1-11 siding on it.
JOHN: And I wanted to put the hardy plank on the outside of it and maybe, possibly, increase the insulation.
TOM: OK. Are you going to take the T1-11 off?
JOHN: Well, I wasn’t going to but I could.
TOM: Mm-hmm. OK. Because you’re going to have the issue of what to do with your windows and the depth around the windows and the trim around the windows and doors and that sort of thing to deal with. But hardy plank is a good choice. What’s your specific question, though?
JOHN: Well, you know, if I put the Styrofoam insulation on between the siding – the existing siding or some sheer wall and the hardy plank, then I obviously have to put some firring strips in to be able to put the hardy plank to and I didn’t know whether or not putting …
TOM: Actually, I’m not sure that that’s the case. I mean if you leave the T1-11 up there – because it’s good sheathing; it’s constructural sheathing – and you attach the foam insulation over that – so you have either pink foam, blue foam, isocyanurate foam, whatever – you can attach that right to the T1-11; then you could put the hardy plank right over the foam, nail through the foam into the T1-11 and have good attachment.
JOHN: Aha. So, how would you attach the foam insulation to the siding?
TOM: With a nail that kind of looks a bit like a roofing nail; it’s got a wide, flat head.
JOHN: (overlapping voices) Oh, OK. OK. Now the only problem I would have with that is that here where we live, up in the foothills, in the summer and it being the south side of the house, the ambient temperature could approach 100 degrees and then in the middle of the night it might get down into the mid-40s.
JOHN: So you would receive a lot of expansion and contraction of the material. Would that have a tendency to pull on the nails or should I use screws or …?
TOM: I don’t think so. I don’t think so.
JOHN: You think it would work.
TOM: Yeah. You would have more of an expansion and contraction issue if you had vinyl siding because it expands and contracts very rapidly and would be all wavy and stuff. But hardy plank is pretty durable in terms of thermal expansion.
JOHN: Mm-hmm. OK. So I just …
TOM: Yeah. You know, it’s not a bad idea to give a call to the manufacturer just to check out your specific situation but I think that’s the way I’d approach it.
JOHN: OK. Alright. Well, then I guess that answers it. Thank you very much.
TOM: Alrighty. You’re welcome. Good luck with that project. Thanks so much for calling us at 888-MONEY-PIT.