I ripped my old shower down to the studs and joists. The studs were rotten, the subfloor was rotten, and the top of the joists (in some places) were weak and rotten.

I plan on replacing some studs and sistering others. Joists I'll likely epoxy and sister before installing new subfloor. I'll be pouring a new concrete shower pan. The issue is that the previous subfloor was 1/2" ply over joists 17 1/2" OC - by my research, not enough support.

First, am I correct in determining 1/2" as not enough support ?

Second, since the surrounding framing and drain pipe are in place assuming a 1/2" subfloor, is my only recourse going to be to cut the base plates, take a 1/4" off the wall studs and extend the drain pipe ?

1 Answer 1


1/2" is a bit thin to span that distance, although it should not be a problem with a concrete slab above it.

If you are worried about it and need to use 1/2" sheathing for other reasons then just install 2x blocking perpendicular to the joist at a shorter distance on center, say 8"-12" O.C. in the area of concern.

As for the wall studs, we would typically leave the wall as is and shore it up from underneath with blocking, also installing blocking along edges of the new sheathing. Therein the new sheathing would not run under the wall and the wall would be now supported by the blocking.

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