Redoing an old subfloor - DIY Chatroom

chhamilton · 03-17-2009, 06:04 PM

I'm looking to lay down new flooring (3/4" hardwood, 4 1/4" wide planks) in my house (built in 1945), and I know that the subfloor needs to be redone first as there are certain rooms with multiple dips of up to 2 inches, and all sorts of 'wavyness'. The current flooring is parquet, and this is visible to the naked eye.

Anyhow, I started tearing up the flooring in one room to see how bad the situation is. The parquet isn't coming off cleanly, so I've been lifting up the (damaged) 3/8" plywood beneath it. Beneath that, it looks like I'm down to the original subfloor, which is 3/4" x 7" planks laid at an angle (20 degrees off perpendicular, maybe?) to the joists. This planking is relatively weak as you feel (and see) it flexing when you walk across it. The joists are 2" x 10", and look to be in good shape, although they're surely off level. They are spaced at 20".

So, what would be the recommended sub-flooring to put in? I was originally planning on ripping up the planks, shimming the joists (maybe sistering the worst offenders), and laying down 3/4" T+G plywood. However, isn't such a floor normally laid on joists that are spaced at 16"? Should my subfloor be thicker because of the wider joist spacing?

Also, one of the walls in this room is a load bearing wall (running perpendicular to the joists). Since the wall was built on top of the old subfloor, I know I'll need to reinforce underneath it as I take up the old subfloor (I want to minimize movement of the wall, and subsequent plaster fixups). I was planning on going joist by joist, and putting in little lengths of 2" x 10" between the joists, under the wall. Is this sufficient? What is the best way to attach these?

Any response would be greatly appreciated!

Chris

Speedball · 03-17-2009, 10:03 PM

Sorry I don't have an answer but I have a similar situation with 3/4" 1'x6" and will be deciding in the next few weeks what to use for the next layer. For my place it may be 3/4" 4'x8' sheets of Plytanium BC underlayment (plywood).

Not sure if this is proper but the only thing I know to do at this point.

Good Luck.

chhamilton · 03-18-2009, 10:35 AM

Quote:

Originally Posted by chhamilton

...with multiple dips of up to 2 inches, and all sorts of 'wavyness'.

That should read 1/2" and not 2" dips. *brainfart*

No comments on how to proceed? I'm mostly concerned about ensuring that the load-bearing wall is properly supported and dealt with.

Also, for all you tile guys: Eventually, I'll be redoing the subfloor of the whole main floor, including the kitchen. In the kitchen, I'd like to put down tile (it's currently a god-awful lino). What would be the minimum recommended subfloor here? Ideally, I'd like the finished height of the hardwood and the tile to be as close to flush as possible. What to people think of using DITRA directly on plywood instead of cement board?

ccarlisle · 03-18-2009, 10:50 AM

Well, from a tilers point of view, a wooden floor system (joists+subfloor) must meet local building codes first and then be placed on joist a maximum of 16"oc to meet most standards I am aware of.

Should also meet the deflection criteria for floor movement and I doubt your system does that with 20"oc joists. Will have to be beefed up considerably with braces.

That is, for a good job where the tiles don't crack on you in a month...anyone could give you less, not many could give you that or more.

Sorry posted a bit quick there. With Ditra, you could get away with 20"oc joists but you'd need a special 3/4" subfloor (maybe even a 3/8" underlayment). See Schluter for exact requirements.

chhamilton · 03-19-2009, 08:56 PM

Still no comments on how to treat the subfloor? (Regarding the load-bearing wall, etc)

chhamilton · 03-20-2009, 05:01 PM

I finished tearing up the parquet and 5/8" plywood, and am down to the planking. Now that I can see the whole area, it turns out the joists are not 20" OC... most are spaced 18", some 16", some 20" and even a few at 24". The planks have had a hard life (I think they've had several subfloors put down and torn up over the years), with a lot of them split and almost all of them crowned or warped in some way. How thick should the structural subfloor be to handle up to 24" joist spacing? What should I put on top of that before laying down the hardwood?