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Unread 07-02-2019, 02:24 PM   #1
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Bathroom remodel, looking for subfloor recommends

I just used the Deflect-O-Lator and received this assessment:
"For joists that are SYP or Douglas Fir, in good condition, 9 inches tall, 1.5 inches wide, 16 inches on center, and 10.5 feet long between supports, the deflection calculated is 0.175 inches.

This translates to a deflection of L / 719.

Since the maximum deflection for tile is L / 360, and for natural stone is L / 720, your floor is rated for Ceramic tile, Congratulations!"
I have the following questions:

1. My initial question had to do with repairing vs replacing the subfloor over the joists. There's a couple of areas of compromise due to long-term water damage, so I was planning on cutting out and replacing these sections, but then started seeing recommendations on just replacing the whole thing (subfloor in the whole room) rather than dealing with matching the thickness of old with new wood (i was thinking plywood). Is there any consensus or general "best practice" on this issue?

2. We've purchased travertine tile in a mosaic pattern (Charcoal Blend Gatsby from The Tile Shop) for the main bathroom flooring (the whole bathroom is about 7' x 7') -

But now with the Deflecto results, I'm not sure our joists/subfloor will be appropriate. Is there any way to improve the deflection "L" rating of my joists/subfloor to accommodate the travertine tile?

3. Lastly, for my walk-in shower (30" x 60") with kerdi shower kit - I was also planning on travertine, in a cobble style. Am I in trouble here too?

Glad I happened across this site - (got here from This Old House forum)

Thanks much for any assistance!
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Unread 07-04-2019, 10:52 AM   #2
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Hi Jose,

For bathroom remodeling I think it's just as easy to replace the entire area as it is to try to patch things in. For stone tiles you'll need two layers of plywood.
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Unread 07-20-2019, 01:34 PM   #3
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thanks John!

Just to clarify for myself re: concern about deflection -
so double layers of plywood as subfloor will suffice vs trying to "stiffen" my joists by sistering new wood or otherwise trying to bolster the rigidity of my joist-structure from underneath?

if so, that would be way easier! - but i just want to be certain before i proceed -

thanks again
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Unread 07-20-2019, 02:32 PM   #4
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No, Jose, it doesn't work that way.

There are two deflection requirements that must be met and you must meet both. They are independent of one another and fixing one does not fix the other.

Your joist structure must meet or exceed the L/720 requirement.

Your subfloor must be in two layers, regardless your joist spacing, and each must be properly, and differently, installed to meet the subfloor requirement for natural stone tiles.

You cheat at your own risk.

My opinion; worth price charged.

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Unread 07-20-2019, 02:41 PM   #5
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Jose - double check the height of those joists; 2x10 are typically 9-1/4” tall. Unless you have a house from before 1950, it would be unusual to have nonstandard sized joists. You should also double check the joist length. Remember that’s the distance between the joist supports, not room size. Since you are wanting to put stone down, you’ll definitely want to verify the 10.5’ measurement.

Running your numbers using standard 2x10 yields a rating of L/766

If the joist really are 9” tall with 10.5’ length, I’d round up the L/719 to L/720 and start working the new subfloor layers.

Last edited by PC7060; 07-20-2019 at 02:52 PM.
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Unread 07-21-2019, 10:03 AM   #6
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PC7060 - yup, double-checked and they are 9" x 1.5"; i'll re-check the 10.5' run too - thanks for the advice! (my brother - architect - more or less had a similar suggestion to yours.)

cx - thanks for the clarification as well!
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