Subfloor material

[bridg73988]

Had a little money to spend and I am going to be working on floor in the near future so I thought I would go ahead and buy the floor material. I have stripped my bus down to metal floor. I am going to treat surface rust and prime/paint. Base will be 2x4 framing and 1-1/2 rigid insulation topped with tongue and groove plywood. My question is what is everybody using for floor material? Treated wood? I would think so but I have been told that the stuff the wood is treated with is corrosive to metal, don't want that! Is Marine plywood different? And is there a particular rigid foam insulation for this application?

[musigenesis]

If you're going to frame your floor with 2X "joists" you could use any insulation that is 1.5" thick - EPS, XPS or polyiso foam board, or rock wool even. EPS is R4 per inch, XPS is R5 per inch and polyiso is R6.5 dropping to R4 or lower in cold temperatures (aerogel would give you a ridiculous R15 at 1.5" along with a much more ridiculous price tag).

For the joists, a lot of people seem to lay 2X4s on their sides; if you ripped your 2X4s into two 1.5" wide pieces you would economize on 2X4s while also making your floor a bit less wood and a bit more insulation.

[bridg73988]

Thanks for the tip, just curious, is ripping just for cost and weight savings? Any idea about what kind of 2x (treated or not)?

[Danjo]

Originally Posted by bridg73988

Thanks for the tip, just curious, is ripping just for cost and weight savings? Any idea about what kind of 2x (treated or not)?

2x2s save on weight. Cost isn’t that much of a difference. Just your standard Douglas Fir is fine. You can buy Douglas Fir in 2x2 dimension

For plywood you’ll want 1/2” underlayment so that you have a nice surface upon which you can glue your flooring.

[musigenesis]

Originally Posted by bridg73988

Thanks for the tip, just curious, is ripping just for cost and weight savings? Any idea about what kind of 2x (treated or not)?

Ripping is for cost savings and a slight improvement in the R-value of your floor; since wood has an R-value of about 1 per inch and is a "thermal bridge" in comparison to the foam board, you want the bottom layer of your subfloor to be composed of as much insulation and as little wood as possible. The best-possible insulated floor is a floating floor with the foam glued to the sheet metal and the plywood glued on top of the foam, and no "joists".

PT lumber would be safe to use but it's more expensive and in my experience it's usually a lot more warped than regular lumber. Also, ideally you seal up your bus to prevent further leaks and ingress of water, so the rot-resistant qualities will be valueless since the wood won't be rotting anyway.

[bridg73988]

I was thinking of using this plywood...
AdvanTech Flooring 23/32 CAT PS2-10 Tongue and Groove Subfloor
A Lowe's near me has it in stock.

[bridg73988]

Originally Posted by musigenesis

ideally you seal up your bus to prevent further leaks and ingress of water, so the rot-resistant qualities will be valueless since the wood won't be rotting anyway.

definitely sealing it up and checking for leaks before starting interior work.

[bridg73988]

I have heard of the floating floor but was concerned about not having things fastened to the metal floor? Am I just over thinking this? If I go that route is there a certain insulation and glue for doing that?

[musigenesis]

Originally Posted by bridg73988

I was thinking of using this plywood...
AdvanTech Flooring 23/32 CAT PS2-10 Tongue and Groove Subfloor
A Lowe's near me has it in stock.

Ugh, wood prices make me ralph these days. I'd go with plywood over OSB but it probably doesn't matter too much. Plenty of people use OSB. I found a batch of super-cheap 3/4" plywood on Craigslist and used that for my floor.

[musigenesis]

Originally Posted by bridg73988

I have heard of the floating floor but was concerned about not having things fastened to the metal floor? Am I just over thinking this? If I go that route is there a certain insulation and glue for doing that?

If the glue fails, your floor might start sort of peeling up, but people usually have cabinets and appliances and walls and stuff that pretty much lock the floor into place anyway. And if you use T&G like you're planning, you won't really get a seam peeling up anywhere.

Most XPS foam board is rated for 20-25 PSI which is plenty for this. EPS is often 10 PSI (but there are higher-rated variants) which would be less suitable but still OK. For a while I was using Liquid Nails to glue XPS board but it wasn't working very well; watched a Youtube video where a guy tested out a bunch of different adhesives to see which worked best with XPS foam and he settled on Gorilla Glue heavy duty construction adhesive. I switched to that and it works very well, producing a tight bond that dries pretty quickly (Liquid Nails takes like a day to cure on foam and never really bonds that well).

[bridg73988]

The Advan Tech said it was moisture resistant, met some kind of "moisture standard". Didn't know if it was any better than regular plywood.

[bridg73988]

Thanks for the info musigenesis, I will have all the usual stuff holding floor like cabinets, couch, bench seat, bed, a divider wall which will all also be fastened to the walls. The floating floor is looking like a good idea.

[musigenesis]

Originally Posted by bridg73988

The Advan Tech said it was moisture resistant, met some kind of "moisture standard". Didn't know if it was any better than regular plywood.

In general OSB is a bit worse than plywood because they'll both get wet with prolonged exposure to water, but plywood will dry out faster and go back to normal while OSB will dry out slower and be permanently damaged so it will dry out even slower the next time it gets wet.

Presumably they can formulate OSB to be better in that area and that's maybe what's going on with this material (it seems to be a lot more expensive than normal OSB but that may be because of the T&G part).

[bridg73988]

On the plywood, with a floating floor, is it worth the extra weight and money for 3/4 or is 1/2 ok to use?

[musigenesis]

Originally Posted by bridg73988

On the plywood, with a floating floor, is it worth the extra weight and money for 3/4 or is 1/2 ok to use?

1/2" is probably OK. You can always buy a sample piece of plywood and lay it on a piece of foam and see if it feels solid enough for you.