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Unread 12-08-2016, 12:38 AM   #1
CamaroRS
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Can I do this to reinforce subfloor for tile and heavy furniture?

Hi all,

I have a question about creating a stiffer floor before installing stone tile and heavier furniture into the kitchen and dining room. I would like to know if my proposed fix will allow me to install 18x18” travertine tile, and also be able to place a 350 lb table in the dining room. The kitchen currently has similar structure with a 250 lb butcher block island.

My house has a crawlspace foundation with 4x6 floor joists, 48”o.c. These joist rests on a 4x4 block of wood anchored to cement piers every 6 feet. The subfloor is 1-1/8” T&G plywood. Overall the floor joists are straight, but there is a lot of bounce in the floor when walking. I think some sags in the floor are caused by the plywood flexing due to the 48” o.c. spacing and heavy appliances.

My proposed fix is to laminate an additional 1-1/8” sheet of plywood from underneath within the joist void, jacking up to level as needed. Then I would sister 2x6s to the floor joists to hold up the new plywood and stiffen the existing floor joists. I also can add 4x6 blocking after all this, but I am not sure how much is required.

Does anyone have experience with this, or can provide some deflection/load calculations after this fix? Is there a way to find out if the modified floor can handle the 350 lb table and stone tile? I know this will be a PITA to install, but if it strengthens the floor, it will be worth it to me.

See attached drawing for an illustration of the proposed fix.

Thanks for the help!
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Unread 12-08-2016, 06:29 AM   #2
Todd Groettum
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That fix IMHO will not accomplish what you are hoping for but I am not an engineer....Flex in the floor is a Very bad sign for Tile, let alone Stone which needs a Minimum l/720 or twice the stiffness as a Ceramic requires...And that is MINIMUM...If you start getting into Large format Stone i would try to exceed minimums where possible....

There are a few around here that may have some idea's but i doubt any of them will be Inexpensive or the fast easy fix you are hoping for...
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Unread 12-08-2016, 07:38 AM   #3
evan1968
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May I suggest a nice area rug?
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Unread 12-08-2016, 08:48 AM   #4
Carbidetooth
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I think you'd be wiser to turn the 2x6s 90° and run them perpendicular to the 4x6 at 16 OC. Even then, I'd question if you could attain L720 without additional support for the 4x6.

The floor system you're described was an engineered evolution of tongue and groove planks on post an beam frame...I don't remember the name or manufacturer.

All that said, I think a consultation with an engineer would be prudent.
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Unread 12-08-2016, 12:20 PM   #5
cx
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Welcome, Andrew.

What you show in your drawing will provide the necessary L/720 joist deflection if the materials are of good grade and species.

The subfloor deflection between the joists is a bit more problematic to calculate, but I suspect what you've drawn would also provide the necessary rigidity there, too. We know that 2x6 car plank flooring in those situations will not provide the L/720 deflection, but I think (without benefit of engineering capabilities) your 2 1/4 inches of plywood might. That presumes, of course, that your added plywood was also oriented with the strength axis perpendicular to the joist structure.

you would not actually meet the spirit of the MIA requirement for a double layer plywood subfloor, but it might still work. The intent of that requirement is to ensure that there is no place on the subfloor where a joint extends from the joist tops through the surface. You won't have that. I suppose you could also add another layer of plywood on top of what you've got, installed as shown in this good article from our Liberry. Given your intended concentrated loads I think I'd wanna do at least that.

I'll also agree with Peter's recommendation above. See my warranty information below.

My opinion; worth price charged.
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Unread 12-09-2016, 09:08 AM   #6
Todd Groettum
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Quote:
The subfloor is 1-1/8” T&G plywood. Overall the floor joists are straight, but there is a lot of bounce in the floor when walking. I think some sags in the floor are caused by the plywood flexing due to the 48” o.c. spacing and heavy appliances.
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