DIY Home Improvement Forum banner

Subfloor

3K views 7 replies 4 participants last post by  cougar01 
#1 ·
I am gutting my 1st floor powder room. I am down to the original vinyl flooring. The previous owners had put another layer on top of the original. To my surprise, the subfloor is only 3/8" plywood. When laying the original vinyl flooring, they used as an underlayment of what looks like some sort of 5/8" particle board (circa 1964 construction).

The subfloor around the toilet suffered water damage in the past and it bows quite badly. I need to cut out the subfloor around the toilet and replace. My question is, can I replace it with the 3/8" plywood as in the original constructions, then lay another solid piece of 3/8" on top and, finally, use 1/4" luan as an underlayment? The current 3/8" subfloor is actually stapled to the floor joists. So, if I screw it in, it should be a bit more solid and less squeaky. I would also use construction adhesive between both 3/8" layers.

Eventually, this floor will have to tie in with the kitchen flooring, which I am certain is set up the same way as above.

Advice or other alternatives are welcomed. Thanks in advance!
 
#3 · (Edited)
I am going to put vinyl flooring back on.

However, upon closer inspection, this is now what I see. The subfloor is 3/8 plywood. This goes under the bottom plates, etc. Then, it looks like they hung the drywall, then laid down the 3/4" particle board (when I pulled the drywall down, there was a 1/2" gap around the perimeter of the room). On top of that, they put down 1/4" plywood, and that had about 4 layers of vinyl flooring on it. So I am guessing that the 3/8" and 3/4" boards were the "subfloors", and the 1/4 plywood was the original underlayment.

I guess I answered my own question....I should replace the 3/8 plywood that I cut out with another 3/8" piece....then lay down 3/4" plywood (gluing and screwing). This would be my "subfloors". On top of that, use the 1/4" luan for the vinyl flooring?
 
#4 ·
OK. Hopefully, this is my last stupid question. When cutting throught the 3/4" particle board with my sawzall, I "accidently" cut into the 3/8" plywood in a small area. The cut is centered between and parallel with the floor joist (16" oc). Is there really any concern to either replace or brace this area since I will be putting down 3/4" plywood overtop everything anyway. I guess the reason for the 3/8" is basically to use as a "filler" to help keep the floors even with the adjoining hardwood floors? In the meantime, I will be sure not to step on the 3/8" plywood so I don't make a quick trip into the laundry room.
 
#5 ·
If you are just trying to remove the 3/4" particle board try setting a skill saw at 3/4" depth and use it to cut where maneuvering space allows. It will work better than the sawsall in sparing the underlying floor, joists, plumbing and electrical that you cannot see from above. Use the sawsall in areas that you can't reach with the circular saw or can see below. And for areas the sawsall can't reach, a hammer and wood chisel.
 
#6 ·
#7 ·
I just did a remodel in a house recently where all the floors were 3/8" plywood with particle board on top of it. Odd, but something they did in the 80's I guess.
 
#8 ·
Thanks!

House was built in the early 60's. From what I understand, this was common construction practice at the time. 3/8" plywood under everything. Wall plates built on top of it. Then, 3/4" particle board on top as the subfloor.

Next question. The 3/8" subfloor that I mentioned goes under the wall plates. On one side of the room, the joist is located back under the wall plate. The next joist out is about 14"- 15" OC. But, from the edge of the bottom wall plate to the joist (the area where the 3/4" plywood would sit) is only about a 10" - 11" span. Is there any concern when I glue and screw in the 3/4" plywood since I won't be hitting a joist along this edge of the wall? I can't add any cross bracing, etc in this joist bay because ductwork is running in it. If I glue and screw directly into the 3/8" plywood, does this give sufficient support? The 3/8" is pretty solid in this area.

The plan is to glue and screw 3/4" plywood on top of the 3/8" plywood floor that runs under the walls. On top of this to add 1/4" cement board for tile. The powder room is about 4-1/2' x 5-1/2' in size. Goofy size. I cross braced in most places (especially under the toilet) to help solidify the floor, but my concern is a lack of a joist to screw the edge of the 3/4" plywood along the wall as mentioned above.
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top