Plumbing – Is a threshold drain outside the laundry room and bathroom, draining to daylight, a good idea

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We are building out a two-room suite that consists of a full bathroom (tub, sink, toilet) and a full laundry room (washer, sink).

There is one single door that enters into this two room suite.

I think it would be nice to have a threshold/linear drain right at that doorway … the wainscoating of the tile in these rooms make them like a swimming pool, so the water can only escape at that doors threshold …

So I am thinking of installing a linear drain that covers the full 32 inches of that doors threshold and draining it to daylight.

Just to clarify – this is not a drain that would see any use under normal circumstances – this is a safety drain in the event that something clogs or overflows or the supply line to the wash machine breaks, etc. – the flow of water is stopped at the threshold of the tile and does not do $50k of damage past that point, It seems like a good idea.

The only thing that nags is that the 2" drain to daylight is a heat sink / source of drafts … so I was thinking of installing a very sensitive check valve, with a 1/2 PSI crack rating, at the end of this 2" pipe.

But now I have a check valve that might stick … but I think I can live with that, since check valve malfunctions cause them to stick open, right ?

Is there, in fact, any problem with draining to daylight ?

Would it be better to put in a huge trap, fill it with water, and just refill it if I ever notice a draft ?

Thanks.

Best Answer

I see several problems with your plan:

  • It may allow mice, insects or other critters to get inside.
  • If it's below freezing outside, the drain will get blocked with ice.
  • The check valve (even if it works properly in the first place) will very quickly get clogged with all the debris that gets washed down into the drain.

If you want to have a floor drain, then it should drain to the sewer, not to the outside. I don't know what the building code in your area says about that, but you may want to check. And you don't really need a floor drain. It's nice to have in some settings, like a commercial kitchen or a public bathroom, but it's overkill for residential.

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