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daveofnj 05-06-2010 02:21 PM

Adequate floor support for new shower?
I am remodeling a second floor master bath. I am planning to install a new shower with 12x12 porcelain tile, a tiled floor, and a glass enclosure on two sides. The shower is 52"x33" with 8 ft. ceiling, so two walls, the floor and ceiling are 81 sq ft. I estimate that the tile will weigh about 500 lbs. not counting the thinset and grout and the enclosure a few hundred pounds, so the total weight of the new shower could be 800-900 lbs. Does that sound about right?

The current shower has an acrylic base and shower enclosure (I think it's acrylic or glass) and thin 4x4 tiles on the walls and ceiling. So, I am going to be adding lots of weight.

The shower subfloor is 1/2" plywood supported by 3 web truss joists spaced 24" oc. The shower is roughly in the center of a 12 ft. span. Because the span is so short the joists are rated at least L/480 according to the span table.

Even so, I am concerned about the extra weight of the new shower. How do I determine if I will get deflection in the joists from the added concentrated weight? I cannot sister the joists. I could possibly add a strongback or two if I tear out the first floor ceiling. Any other thoughts? Thanks.


oh'mike 05-06-2010 06:27 PM

I don't like the flexing that happens with those web trusses. Add to that 24" centers.

I'd be concerned too. The short span of 12 foot may be your saving grace.

Is there any easy way to stiffen them up by 'boxing' them with 1/2 inch plywood on both sides--glued and nailed?

Then a subfloor of 3/4 ply topped with another layer of 1/2 inch ply--that should do.

Someone will jump in with span tables---I just haven't had great luck with those webs without boxing them.---Mike---

I did build a large bath over webs four years ago---glass block shower wall--no call back----Yet-

boman47k 05-06-2010 07:21 PM

Unless I am reading this wrong, it looks like the main difference in weight wilol be between the old and the new shower. How much difference in weight can there be in a 12x12 tile and 9 4x4 (12x12) tiles plus the extra grout? Just curious about the weight difference. No i dea about the web trusses on 24 " centers.

L/480? What is needed?

daveofnj 05-06-2010 07:46 PM

Thanks for the replies.

I could box segments of the joists but the plumbing would prevent me from boxing the whole thing. That's why I was thinking of strongbacks. Or I could try a combination of the two.

I guess the extra weight is from the tiles, the new enclosure and the base may be 300-400 lbs. The old 4x4 tiles are less than half the thickness of the new tiles, the new shower enclosure is much thicker/heavier than the existing one and the shower base is going to be mortar + tile rather than acrylic. I am especially concerrned because I have joist deflection in other areas of the house.

oh'mike 05-07-2010 04:17 AM

Boxing what you can and stiff backs should do it---It is only 12 feet---Those web floor trusses are no longer used in my area---I am glad .---Made for a springy house.---Mike---

Bud Cline 05-09-2010 02:27 PM

You could easily reduce the total weight of the shower receptor to about 8 pounds plus the weight of the tile if you used a Schluter System Shower Kit. The wall tile is basically negligible anyway because of its distribution over the wall area.:)

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