Replacing damaged sub floor

evolve · 11-08-2007, 02:29 PM

Hi All,

Hoping someone can give me some pointers. Because of water damage and mold I had to rip out the sub floor in my laundry and half bath. It was 3/4" OSB. Now, I need to replace it. When cutting it we left about 1-2" of flooring along the edge of the wall. I was told that all I needed to do is sister the joists at the edges to provide a base for the new sub floor. Sounds easy enough. Well, at one side of the room this should be pretty easy. I think I could even chisel away the 1-2" and use the existing joist. The other side however isn't as simple. It's a wall to the outside and the joist sits about 6-7" (rough guess) back behind (below really) the wall from where the original floor was cut. And, there is a bunch of plumbing to work around. Washer and sink and a pipe going out to the sprinkler system.

I'm not sure how I'm supposed to sister this joist to provide a stable surface for the sub floor. I don't know that I can. For one the new joist won't be far enough out for the new floor to rest on. But also, how do you sister around the all the plumbing? Would I be better off putting in new joists that run perpendicular to and in between the outside joist and the next one over? Should I remove the original OSB under the wall? Not sure what the proper way to go about this is.

Any suggestions? Many thanks.

JazMan · 11-08-2007, 05:16 PM

It's called "blocking". You run a 2x4" or wider, perpendicular to the joists and screw both sides of the subfloor into it. Do not remove the subfloor that is under the wall, how would you replace it?

What are your plans after the new subfloor is glued and fastened in place? Make sure you use subfloor grade, exposure 1, exterior glue material that of course is tongue and groove.

Jaz

evolve · 11-08-2007, 06:03 PM

Excellent, thanks for the reply. That doesn't sound too difficult. How many pieces should I use? The distance between the walls, span of the OSB, is about 7'. Is a 2x4 really all that is needed? I would have thought it would need to be the same size has the joist. Also, these are I-Joists. Anything special I should do different?

>Do not remove the subfloor that is under the wall, how would you replace it?

Hahah, don't ask me. I never thought of the idea until I read something on this forum that sounded like that's what someone else did. I started thinking leaving the 1-2" was the wrong thing to do.

evolve · 11-08-2007, 06:16 PM

Either porcelain or maybe Slate or maybe even Travertine. Not sure yet but it will be tile. I'm not sure if I'm going to try to do the install myself or not.

JazMan · 11-09-2007, 12:52 AM

You put the lumber flat under the seam and screw it in so the two pieces of sub don't move up and down. You can check with the manufacturer's website for more info.

What brand are these I joists? One of the most popular brands is Trus Joist by Weyerhaeuser. You also need to know more specific info to find out what the deflection rating your floor has. Brand, style name, size, width and unsupported span.

You may be limited to ceramic or porcelain because natural stone tile requires a very stiff floor and from what I've seen I joists in general are limited to a lower deflection rating spec unless the house was built knowing natural stone tiles were being specified. You will also need to add another layer of plywood along with an isolation membrane or a cement backer board.

Jaz

jhen · 11-09-2007, 07:31 AM

Spammer - Edited

evolve · 11-09-2007, 03:45 PM

The are Weyerhaeuser, 16" apart and 12" in height. The information on them reads..

Exposure 1
454
Structural 1 Rated
Diaphragms - Shear Walls
PS 2-92 Sheathing

This is above a crawl, btw.

>You put the lumber flat under the seam

Not entirely sure what you mean but, I'll check the Weyerhaeuser site and see if I can find some specifics.

Many thanks for the help.

evolve · 11-09-2007, 07:35 PM

Actually, I don't think they are Weyerhaeuser. There is a W looking logo on them and I just made the assumption. Most of the writing on them is very difficult to read but I'm sure they are LP. And they are 11 7/8".

I've been reading about blocking a bit. Looks like I should use a backer block and a hanger. But, I'm seeing references to top mounted and face mounted hangers. Does it matter which I use? I think I'll have to use the face mounted given I can't get access to the top of the joist that sits back from the wall.

I was able to find this PDF which has a lot of info in it.

evolve · 11-10-2007, 02:06 PM

Do I need to block with an entire I-Joist or would simply blocking against the flange of the I-Joists be sufficient? There's a lot of plumbing and working around it is going to be a real hassle. It would be really convenient if I could just block against the flange of the I-Joist with a 2x4. That said I want it done right and I don't want a sloppy job.

Thanks again.