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Floor deflection

2K views 12 replies 8 participants last post by  EthanB 
#1 · (Edited)
A 'little' background first:

So I'm not a tile guy (or a guy for that matter :whistling) I usually do finishing carpentry. Mostly crown and wainscoting.

My grandfather owned a tile setter business before he retired, and I used to spend my weekends and summers helping him to make a little pocket cash, so I do have some fundamental ideas about what it takes to set tile right.
This was about 10-15 years ago, in Belgium, where I was born and raised.

One of the big adaptations for me in the US have been setting tile on wood for the very first time (which still feels very very odd to do).
Belgium has no wooden floor joist. All construction is done with concrete/brick. So even on second/third floor bathrooms, you set tile on a concrete slab... always.
Putting an underlayment on plywood with thinset feels just... wrong... :no:

Anyways. A couple years ago we bought a 1970s house that has been stuck in time. No work was done in this place, ever (to the point that we still had the original drywall primer, not even paint on the walls when we moved in).

That is with the exception of them replacing the vinyl tile in the kitchen with marble to make the house more presentable for the sale, in a room that has a deflection of L/120.
As expected, it failed in short order, and now it's time to replace it.

I've got 1.5x9 (actual size) joist that span 19'. Unknown species, in good condition, and 1/2 particleboard sub-floor (yes particle, not OSB). There is an unfinished full basement underneath.

I'm replacing the particleboard with 3/4 EGP plywood. (Ditra on top).
From what I'm reading about joists/deflection, sistering the joist doesn't seem like it'll be enough in this case.
Instead I'm planning on putting in two beams in the room below, at the 1/3 points, cutting the joist spans down to 6'.

However, seeing that I have literally no experience working with, or accounting for wooden joist, how they behave and what it takes to stiffen them up enough to make them suitable for tiling, I though I'd check in with you tile gurus first, to make sure that I'm not making some completely obvious dumb-ass mistake, because despite doing my research/homework the last few months, I really don't have a clue what I'm doing.

Any advice, tips, tricks?
 
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#2 ·
All you need is one beam to break the span, make it right down the middle or offset to one side to have a 12' span and you good to with the tile, just make sure you have your subfloor screwed down and if you using ditra you good to go.
 
#5 ·
What you are trying to accomplish is to stiffen the floor and not change the loads to another area. At least that is what I think you ought to be thinking of.
You might look into sistering the existing 2 x 10s with at least one 2 x 12 each. the 2 x 12 probably does not have to go the full length of the 2 x 10 and land on the walls. Keep them shy of the support walls by a few inches if you want.
I would recommend using 16d sinkers at about an 8" staggered pattern. You can glue if you want but probably not really necessary.

Fast and easy and you don't lose but about 2" of head room.

Andy.
 
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