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Matt05DIY 12-31-2021 12:18 AM

Shower project advice request
1 Attachment(s)
Hello everyone,

First time poster but I’ve been reading through various threads for a bit. I had originally started posting about this in another forum but thought I’d take it over here for additional advise.

Basically what started off as plans to regrout my shower turned into a complete tear out once I realized there was water damage behind the wall opposite the shower head. Shower consisted of a insert shower pan with tiled walls. Home was built in 73 and the tile only had drywall behind it with no waterproofing so I completely tore the tiles and walls out. Subfloor was 1/2 plywood and it had joints that weren’t even resting on the joist below so I recently just took that out as well and that’s basically where I’m at right now.

I attached a picture with the floor removed. Still need to clean up the edges a bit but I should be able to get it cut flush with the wall. I’m a complete first timer for a project like this so just taking things one step at a time and trying to figure it out on the go. Couple questions I’m hoping i can get help with.

First I’m wondering what I need/should do to strengthen the subfloor as far as sistering joist and what not. Hopefully someone can give recommendations based on the picture. The joist are 2x8. I think I’ll definitely have to sister the joist closest to the tile floor as there’s not enough of it exposed to screw the new subfloor down to.

Second is I’m wondering if I need to match the old subfloor with 1/2 plywood and then add another layer of 3/4 or can I just go straight for the 3/4 since the cut is flush with the walls anyway.

Any other advise going forward id appreciate. Nothing is set in stone but right now I’m leaning towards going with a premade Kerdi base and curb and tile just FYI. Maybe even using Kerdi board for the walls. Let me know if any additional info is needed.

Thanks for any input!


Kman 12-31-2021 12:52 AM

Welcome to the forum, Matt. :)

I see the ends of those joists are sitting on top of a wall, do you know how far that one in the left of the picture spans?

You'll need blocking all the way around the perimeter to support the plywood edges. It can be notched as needed to allow for the plumbing and cable that I see. Just notch it no more than necessary.

If you're planning to use a tray, then I would take this opportunity to make sure the joists are all flat and level. The foam trays require a level floor for proper drainage, and there won't better time to do that.

After that, you can install 3/4" plywood, glued and screwed to the framing. Is the shower 4x8 or less? If so, you can get it all with one sheet, but you'll have to cut it into two pieces so you can install it with the face grain running perpendicular to the joists. If you use tongue and groove plywood, you won't need blocking at the one seam.

Matt05DIY 12-31-2021 11:27 AM

Thanks for the reply. So the dimensions of the shower are 48"x32". Yeah the joist are sitting on an exterior wall on the right side. The joist are generally 16" OC in my home however it appears the partial joist in the center that they cut was the original so the sister joist attached to it is 18" OC from the joist by the wall and about 14" OC from the joist where the tile floor is. It's a second floor bathroom and unfortunately I can't tell how far the joist runs before being supported because there is blocking between the joist about 12" under the wall obstructing my view. If it's the same as my first floor though it should be just over a 11' span from looking in my basement.

So I'll need blocking on all four sides around the perimeter, it won't be enough to just screw the plywood into the joist?

Kman 12-31-2021 09:51 PM

So let me rephrase that a little. All edges of the plywood have to be supported around the perimeter. A joist, properly sized and supported, will work for that.

Make sure not to screw or nail into that vent on the back wall.

Matt05DIY 01-02-2022 06:19 PM

2 Attachment(s)
Just dry fitting the subfloor support pieces before I put them in. Out of the two below pics which is the best way to position the 2x8 support? Also what is the best way to fasten it up?


cx 01-02-2022 06:53 PM

You could do that either way in your application, Matt. Your pieces don't need to be any larger than 2x4s for your purpose, but larger pieces are usually easier to fasten adequately.

My opinion; worth price charged.

Matt05DIY 01-06-2022 12:59 PM

Appreciate all the input so far. I’m looking to get the subfloor project done this weekend so wanted to run my plans by you guys to see if I’m on the right track.

For the purposes of explaining my plans well call the edge closest to the tile running parallel to the joist the south edge.

I plan on doing a partial sister of the 2x8 joist on the south edge about 4.5 feet long using glue and 2 7/8 headlock screws in order to have more joist exposed to screw the floor down to. On the east and west edge I’ll just block it perpendicular to the joist with either 2x8s or 2x6s. The north edge should be fine since I have a good amount of the joist to screw onto.

Finish it by glueing/screwing 3/4 inch plywood down, possibly a second layer. My understanding is you want the long end of the plywood to run perpendicular to the joist. Since my area is 48x32 could I just cut the long end down to 32” and use a single piece to cover the whole thing?

Also wondering if my floor will be able to support tile or if I should jus tout another solid shower base in again which is what I had before. The rest of the bathroom is 12x12 tile and seems to have held up fine.

Final question . Would adding another partial sister joist to the center joist running just a short distance between the west wall and stopping short of the drain pipe be beneficial at all? I’ll have extra 2x8 left over so just seeing how I can beef it up more.


Matt05DIY 01-13-2022 12:55 PM

1 Attachment(s)
This is what I came up with for blocking the edges for the new plywood floor. My only concern is the section with the pipe in it. I could only fit a 3/4” piece of wood (poplar) across the span because it was all that would fit over top the pipe. Is this going to be adequate or any ideas how to reinforce it?

I think I’ve decided on just putting in an acrylic shower pan in but I still want the subfloor to be as solid as possible.


jeffnc 01-13-2022 01:35 PM

That looks pretty good so far. Not sure what the extra pieces of wood in the U shaped area are, but anyway - what I'd do with that piece over the drain pipe is screw it to the bottom plate of the wall, as well as toenail the ends. Or maybe that's what you did, hard to tell from the picture.

ss3964spd 01-13-2022 03:01 PM

I think he built the "U" then slipped it into place and secured the two sides to the joists. Probably easier than trying to toe nail/screw the single 2X between the joists while keeping it at the right height.

Matt, don't think you'll be able to toe nail through the 3/4" edge of that poplar without it splitting. Perhaps you have some cleats installed against the joists upon which the ends of the 1X poplar sits.

I think it was mentioned above, you might also consider securing those two joists that overlap above the load bearing wall below. Toe screw them into that top plate, and at least screw, if not bolt, them together. Get some wooden shims, coat them with wood glue, slip them into the gap, then screw/ bolt. That way you're not trying to draw them against each other.

Matt05DIY 01-13-2022 10:55 PM

Thanks for the replies. Dan is right above the "U" block. So far the board over the pipe is just screwed to the bottom plate. I also think it would be difficult to toe nail a 3/4" board and like the idea of screwing in cleats under it. Originally I was going to put a 2x6 underneath the board vertically for support that was notched to accommodate the pipe but the board actually snapped trying to hammer it into place due to the notch having weakened it.

Regarding the overlapping joist I was surprised to see they were only held together with two nails. I added a third nail but will probably follow your advise and take extra steps to secure them together. Although I guess it held up over what I assume was almost 40 years.

jeffnc 01-14-2022 07:37 AM

OK I missed the part about that being 3/4". You can still toenail it if you predrill the holes (I almost always do that anyway near the ends of boards). Not sure how much that would buy you.

ss3964spd 01-14-2022 09:40 AM

Securing those over lapping joists probably isn't a big deal, Matt, if you do indeed go with an acrylic shower pan. The reason for securing them is to prevent "scissoring".

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