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My contractor is installing a 3/16" plywood as a shower pan subfloor on 16" floor joists. It is for a curb-less shower. I think they did that because they built the floor too low to allow water drainage and now has to

  1. Cut into the joists for the slope
  2. Use 3/16" plywood as subfloor (44" x 76")

I am very concern about the integrity this flooring. My questions are:

  1. Is this safe?
  2. What are the potential problems?
  3. How long can it really last? It's newly built and seems OK now but over time moisture could erode underneath things can fall off. It just looks very fragile.
  4. What would the fix be?

3/16" plywood subfloor cut joists

manni
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    Not even close. Decking on outdoor decks is typically 1.25 lumber, and on 16" spans you can feel it flex if you bounce on it. 3/16 it'll sag and crack instantly. – whatsisname Nov 11 '21 at 07:57
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    I feel for you... this is a spectacularly terrible job in so many ways. I hate to say it, but I think you might need to start thinking about having a non-curbless shower. Is this bath on the first or second floor? What's underneath? (I'm assuming it's finished space underneath, but if it's a basement and you can steal a bit of ceiling height, you might have some options that keep the curbless.) – Aloysius Defenestrate Nov 11 '21 at 14:28
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    As a further aside, start looking for a competent contractor. You might try to get this one to fix things, but I wouldn't hold my breath. Don't pay another dime. (And stop recent checks if you can.) – Aloysius Defenestrate Nov 11 '21 at 14:29
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    This is on the first floor. Beneath is concrete slab so no more space to steal. I wish finding a competent contractor were easy in the bay area. All general contractors I've dealt with have been terrible. – manni Nov 11 '21 at 19:26
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    Those unlevel joists are enough to make the tile crack the first time you step on it. If the contractor knew from the beginning that you wanted a curbless shower and built that floor then don't you dare pay them another dime. If your curbless shower is a "change order" then it's still their fault for not quoting you enough to re-do the floor framing properly. If they "cut you a deal", well you're face-to-face with that ill-fated choice now. – MonkeyZeus Nov 11 '21 at 20:51
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    They could wedge pressure-treated support blocks between the slab and the bottom of the joists in various locations to make it solid enough and shave the joists more to accept an underlayment of proper thickness. This would be of course cobbing the job further. – MonkeyZeus Nov 11 '21 at 20:54
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    The contractor built the floor and they knew I wanted curbless shower. This is all on them. – manni Nov 11 '21 at 21:47
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    Having a slab underneath is actually a really good thing. It means you have a fighting chance at having a decent subfloor, because you can build support for the subfloor off the concrete (as opposed to having hacked away floor joists that wouldn't really hold anything substantial). – Aloysius Defenestrate Nov 12 '21 at 02:11
  • Well, you should demand an underlayment of proper thickness. If you demand brand new floor framing then they might just leave you high-and-dry. You'll have an unfinished shower for months and the next contractor will charge you extra for having to deal with someone else's cob-job. If they seem receptive to solutions then present the "pressure-treated wedge and further joist shaving" solution. The biggest issue is those deep notches for plumbing and they might be unavoidable even with new framing so the support wedges will be crucial. – MonkeyZeus Nov 12 '21 at 14:24

2 Answers2

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Is this for a threshold free tiled shower floor?

3/16" - that's a joke.

TCNA requires 1 1/4" subfloor for a tile installation.

Assuming the contractor tiles on top of 3/16 and grouts it. The grout will crack almost immediately. What waterproofing system are they using? Hotmop, kerdi, red guard?

The fix is getting a competent contractor.

Also it looks like someone knotched all the strength out of your joists. The dimensional floor members were probably 2x10 but it looks like they've reduced them to be the height of a 2x4 at the notch. For a back of hand strength comparison of those members you take the square of the inverse so a 2x10 is 100 in comparison to your 2x4 which is 16. So your floor member is now 80-90% weaker - it doesn't even look like they left you 4" of depth on that 2x10.

Fresh Codemonger
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    Quick! Call your building inspector in to have him take a look at this! Even if it costs you $100 or more to have him come for an inspection that you know you'll fail, it will force the contractor to fix it all on his dime for creating this mess. – FreeMan Nov 11 '21 at 13:21
  • I really doubt they've shaved off more than an inch from the floor joists. If they cut a 2x10 down to 2x4, they would have plenty of room for a proper subfloor. I think they've taken out about an inch and are going to make that up with 3/16 of subfloor and 1/2" of tile and water barrier to get a very slight slope and be close to the level of the rest of the floor on the edges. Still, it's a terrible job, but not that exaggerated. – JPhi1618 Nov 11 '21 at 17:07
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    @JPhi1618 You're talking about shaving off the top, but that big ass notch taken out from below for the Y, and the angled pipe further up already reduced the joist to a thin piece. – Logarr Nov 11 '21 at 17:13
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    @Logarr, You're right. I was focused on one dumb thing and became blind to all the others. Now I have to wonder if they ran the new ABS drain pipe or if it was like that and they "just" shaved the top. – JPhi1618 Nov 11 '21 at 17:15
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    It is for a threshold free tiled shower floor. I will try to get an extra inspection. The city doesn't make it very easy to find them. – manni Nov 11 '21 at 19:35
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    "knotched" - good portmanteau! – Suncat2000 Nov 11 '21 at 22:17
  • @manni Did your contractor install the plumbing drains in the floor, or were they already like that? – J... Nov 12 '21 at 15:25
  • Even worse than that, some sections have had the bottom cut out to run the pipes under and are now only about 2"x1". – shoover Nov 12 '21 at 16:37
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    @J...They also installed the plumping underneath. They did everything from scratch. – manni Nov 12 '21 at 17:22
  • @manni Then they absolutely need to fix the structure work on the joists also. In any case you would want to have that fixed, but if it was your contractor who destroyed those joists then they should be the ones to fix it - on their dollar. – J... Nov 12 '21 at 17:32
  • @manni Between the massive notches cut for plumbing and the "shaving", he's completely destroyed your floor joists. That whole section will need replacing – element11 Nov 12 '21 at 17:35
  • @J...I am really in a bind here. The contractor insists that they're professionals and everything is fine. As MonkeyZeus mentioned, if I make them replace the flooring they could just leave and not come back and the next contractor would charge me much more to fix. I am hoping the city inspector will take a serious look at this. – manni Nov 12 '21 at 18:08
  • @manni The joist work is definitely not fine. You might get away with reinforcement like this in the worst areas, but it's hard to say without knowing what the rest of the house structure looks like and where those joists span. – J... Nov 12 '21 at 18:26
  • @manni this is directly on a concrete floor? This isn't a second floor? That may be why the contractor thinks the joists are fine if they aren't holding the same load as a typical joist. – JPhi1618 Nov 12 '21 at 19:04
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    @JPhi1618 This is a raised floor about 2' directly above concrete slab. – manni Nov 12 '21 at 19:10
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    So this floor assembly is over a 2' crawl space. This makes fixing it way easier, it certainly doesn't mean the joists are fine. Also they have a 2' crawl space and they decide to cut the crap out of the floor joists to run the plumbing? I am highly resistant to firing people and would almost always get people to fix up a job. In this case I'd fire them. This is one of the most horrible jobs I've ever seen - sorry you are in this situation! – Fresh Codemonger Nov 13 '21 at 03:37
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Per IRC-2018 table R503.1, a subfloor on 16" centers requires 5/8" minimum.

https://codes.iccsafe.org/content/IRC2018/chapter-5-floors

The same minimum required by every manufacturer of backer board that I know of.

Is it OK to use 1/4" concrete backer board over 1/2" plywood as a bathroom subfloor? No, 5/8" minimum always for any floor anywhere.

3/16" plywood is for use upright, or as a shim over a subfloor that already meets spec.

"minimum" - Use 3/4" T&G and backer board. I've never even seen 1-1/4" plywood.

If you want curbless you need to raise the height of the entire rest of the floor and have a nasty transition at the doorway. Up to you. Curbless is silly IMO; how you gonna put a door? (no door? That's even sillier; sounds cold).

At this point I wouldn't want anyone to see it or they'll make you redo all of it.

Mazura
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