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I'm installing the DWV plumbing in my new addition. I've located the toilet flange and have temporarily screwed it to the OSB subfloor using a couple of coated decking screws so I can continue with the pipe installs.

What kind of screw material is recommended for the permanent installation of the toilet flange? I'm thinking along the lines of:

  • Treated deck screws
  • Stainless steel screws
  • Galvanized steel screws
  • Plain ol' "wood" screws
  • Something else

Water should never touch these screws, so rusting out should never be an issue, however, theory & reality rarely match up and I'd think that most here have dealt with a leaking toilet at least once in their lives and have seen bolts & screws rust out. I'm trying to decide if that's enough of a concern to invest in a more expensive rust resistant/proof fastener or if I'm overthinking it.

I'm not particularly interested in size/length questions, as I already know that a #10 or #12 is the right size for my flange, and it's only going into 3/4" OSB, so it doesn't need to be any longer than 1".

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  • "should" and "real life" disagree regarding rusty toilet screws. Condensate, quite common in summer weather, if nothing else, will get them. Any leaks, no matter how tiny, will as well. For the same reason, folks who have been down this road once tend to waterproof wooden flooring under a toilet, and the edges of the hole the flange is mounted in.
    – Ecnerwal
    Commented Jan 27, 2023 at 15:04
  • Ah, waterproofing the floor, that's a good idea. I suppose I should ask a whole 'nuther question about that... Fully understand the difference between theory and reality - that's why I asked the question, @Ecnerwal. Do you have a recommendation?
    – FreeMan
    Commented Jan 27, 2023 at 15:06
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    Common to use the same paint-on stuff you'd waterproof tile with with - redguard or maipei's green stuff that's pretty much the same thing. Can't see the membrane products doing well with the shape. A coat of leftover exterior paint is better than nothing, especially with it being OSB.
    – Ecnerwal
    Commented Jan 27, 2023 at 15:11
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    Any reason why brass or stainless steel (as in Ecnerwal's answer) would not just be the immediate go-to?
    – spuck
    Commented Jan 27, 2023 at 17:02
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    In theory, there is no difference between theory and practice, while in practice there is...
    – gnicko
    Commented Jan 27, 2023 at 21:15

4 Answers 4

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Stainless steel or brass/bronze.

We're talking a very minor incremental cost unless you patronize an utterly ridiculous hardware store.

"Should" and "real life" disagree regarding rusty toilet screws. Condensate, quite common in summer weather, if nothing else, will get them. Any leaks, or splashes/spills near the toilet outside, no matter how tiny, will as well. For the same reason, folks who have been down this road once tend to waterproof wooden flooring under a toilet, and the edges of the hole the flange is mounted in.

You might want to add some material (blocking) below the floor so you can use longer screws, particularly with an OSB floor. A bit of scrap lumber might make a world of difference.

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I would stay away from the coated deck screws. I had terrible results from using them on a deck no less. You say there will be no water contact, well stuff leaks so stay away from regular wood screws and even galvnized. I'm at the point where I use stainless steel for everything that's questionable.

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  • I knew the deck screws were, most likely, going to be temporary. They were the only ones I had of sufficient diameter and not too much length for the temporary hold down. Also, yes, I know theory & reality rarely match up, hence the question.
    – FreeMan
    Commented Jan 27, 2023 at 15:11
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Treated deck screws Stainless steel screws Galvanized steel screws Plain ol' "wood" screws

Use Stainless steel and forget about the rest

Also the toilet flange and bolts should be s/s

There is noting more nightmare then finding the bolts the ring and the screws totally rusted

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Always use stainless steel screws to secure a toilet flange. Anyone who put other type of screws in has no business building toilet flanges in the first place. If the toilet bolts break the flange and it must be replaced, the stainless steel screws won't ever rust so they can still be removed

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