LESLIE: Charles in Ohio, what’s going on at your money pit?
CHARLES: Hey, hi. I was trying to find out if there was a way that I could strengthen my subfloors; meaning I have wooden floors that have – just cracking and popping. My house is three years old.
TOM: OK.
CHARLES: And I was wondering if I can strengthen the floor with foam insulation. What do you guys think about that?
TOM: Well, I don’t think foam insulation is going to strengthen the floor. What floor are we talking about making stronger?
CHARLES: Well, I am – you know, unless I’m down in my basement …
TOM: Right.
CHARLES: … and I’m looking upward – I have the – my subfloor.
TOM: Right.
CHARLES: And what I was wanting to do is insulate it for sound and strengthen it at the same time. Because when we walk in the family room above from the basement, it – there’s, you know, cracks and squeaks and so forth. You know how a floor gives and …
TOM: It’s a three-year-old house. Do you – what kind of floor joists do you have? Do you have solid floor joists or do you have floor joists that look like plywood beams?
CHARLES: No, it’s a solid floor joist …
TOM: OK.
CHARLES: … with the – what is that? – that compressed wood or panels on top of it.
TOM: Yeah, like a wafer board or something like that. Mm-hmm.
CHARLES: Yes, sir. Mm-hmm.
TOM: Yep. Well, in terms of making the floor stronger, insulation foam or fiberglass is not going to make it stronger. It will quiet it down. And as far as the insulation is concerned, do you want to keep heating the basement area? Because that’s what that’s going to do.
CHARLES: Keep heating?
TOM: It’s going to heat – yeah, if you’re – is this is a finished basement?
CHARLES: Well, half of it is and the other is the unfinished side.
TOM: Alright, well then you can insulate the floor structure between the floor joists.
CHARLES: I got this idea from a show on PBS where this fella did this to his attic. And he was looking to strengthen it a little bit and I thought, “Oh, what a great idea.” But I really didn’t want to go over my head and tackle this project on my own. I wanted to get with an expert.
TOM: Charles … Charles, never believe what you see on home improvement TV shows. (laughter) It’s all make believe. (laughing)
LESLIE: Hey, that’s not true.
CHARLES: (laughing) OK. Well, this is why I’m asking.
LESLIE: The insulation will definitely help baffle the noise …
TOM: Yeah.
LESLIE: … and keep the basement warmer, but it’s not going to add any structural integrity to the floor or the joist.
TOM: Alright, Charles. Thanks so much for calling us at 888-MONEY-PIT. 888-666-3974.
We’ve worked on and lived in many early 20th century homes and are very familiar with the floor noise isses. In our current 1920 bungalow rehab, I can confidently say that an inch of spray foam between the floor joists made a world of difference in noise, squeaking and movement of the main floor hardwood floors- far more than we imagined. It even feels more solid when you walk across them. I’ve read many times and heard from building officials and architects that spray foam does provide structural stability, so it makes sense. Between the foam and the rockwool we added you can hardly hear a thing when someone walks across the floor upstairs. It used to be very loud. We have expanded into the attic and are considering spraying the underside of the stairs similarly.