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Tomorrow we are roughing in the plumbing for a renovated claw-foot tub in a house we’re remodeling. The plumber called and said he’s concerned about the strength of the floor, which is 3/4″ T&G over joists 16″ O.C. The plumber wonders whether we should overlay another 1/2″ or 3/4″ of plywood before the tile floor goes down.
The tub is about 4′ 6″ long by 30″ wide and is not of the “deep” variety, but it still is very heavy. It will be heavier yet when filled with water.
My tile man plans to use a layer of felt, galvanized mesh, and 1″ of mud for the tile which itself will be about 5/16″ thick when set.
All this could add up to quite a rise at the threshold to the bathroom.
We have access from below to add blocking between joists to strengthen the floor in the area where the tub feet will rest, and I’m tempted to try this approach.
The client has selected some high-$ fixtures which will rise from the floor, and the plumber needs to know tomorrow what the finished floor level will be … thus the urgency.
Thanks in advance for your help, Steve
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You have to look at what the issues are. Extra plywood under tile is used to stiffen the floor membrane for tile. It does very little to strengthen the floor. 3/4" plywood over joists at 16" oc is fine for a full 1" float. Concern for the feet of the tub falling through the plywood are unfounded. So the question is, are the joists adequate? You don't say what the size or the span is, but to be on the safe side you could double up to 8" oc under the tub. This will reduce the loading on each joist and the plywood span by half. Cheap insurance.
*Excellent thinking, Mike. The Joists are 2x8's, spanning only 5'. Each bearing point is on a CMU wall carried down to a strip footing. I think we can slip in more joists as you suggest, and we could do that after the plumbing rough-in but before the tile floor goes down.I'm still open to alternatives.With gratitude, Steve
*Mike: Did it today as you suggested. Tile guy will be on the job tomorrow, and we're still on schedule. Thanks again for a straight-forward solution!Regards, Steve