Deflection in hall

[Saint Toro]

Hi all, I have a deflection problem in my hall (12ft span x 5 ft wide- block wall one end and beam at the other) and i want to install some travertine stone tiles (18" square, 1/2" thick). The floor is only 5/8" plywood over 2x8 spaced 16" OC. There is a height problem as well wth the ajoining kitchen floor (always several problems to deal with). Can I reinforce the floor with a wall in the basement (unfinished, concrete floor) to minimize the deflection or get rid of it altogether, cutting the hallway span to 6 ft between bearing walls? are there any problems with doing this? (the wall isnt a problem in the basement, it falls in a good spot for a closet), another question: 1/2 " backer, or 1/4" backer? ( I would prefer 1/4" b/c of the hieght problem) does it provide any structural integrity? thanks for any help or advice

[Brian in San Diego]

Saint Toro,

Welcome to the forum! We'd like to know you on a first name basis so if you would, please click on the User CP tab in the dark blue toolbar above and edit your signature line to include your first name.

You can definitely add a wall in the basement as a means for shortening the span and achieving the the L/720 criteria for setting a stone floor. That's only half the equation. You need two layers of wood (generally plywood) totalling 1 1/4" of thickness for a stone installation. In addition you need to add 1/4" backerboard or a membrane such as Ditra to set tile on. If you have complete access to the subfloor from below it may be possible to add plywood in between the joists and cleat it in place. That would depend on access and interferences. I have not done that operation and it needs to be done properly to be successful. If that is something you would be able to do, let us know and someone will be along to help out.

Backerboard adds no structural integrity to the subfloor system.

Brian

[Saint Toro]

Thanks the the repy, so regardless I need to put another 5/8" on top to get the 2 layers -1 1/4" of wood subfloor? (out of curiosity why is 1 1/4" of ply needed -handy but dont tile much?) My floor that butts up against the hallway is 3/4" above the subfloor (3/4" oak hard)that makes my hall (5/8" ply+5/8" ply+1/4" backer +1/8" mortar +1/2" tile=2 1/4") 2 1/4" thick in total and 1 1/2" higher than my kitchen - it sounds like im up the creek - unless i go from underneath - am I understanding this correctly (it's sounds like it's one of those times when i hope i am not!) thanks for the continued help

[Brian in San Diego]

Mark,

The double layer of ply thickness to 1 1/4" is basically the same theory as beefy joists with a short span to meet the L/720 deflection rating. It's to provide a stable surface with little deflection between the joists. If your heart is set on stone, I think the 3/4" ply properly cleated under the existing 5/8" subfloor would do the trick. If you used Ditra instead of CBU, you'd lose 1/16" there, so you'd have 3/16" (Ditra), 1/4" (thinset) and 1/2" (tile) or 15/16" above your existing 5/8" plywood subfloor. Your transition to the hardwood floor would be 3/16" hardly enough to worry about. If that seems like too much trouble or you don't have the access to pull it off, then you could add 3/8" plywood, ditra, thinset and ceramic tile and end up with the same thickness. Schluter says the minimum plywood thickness on 16" centers for a ceramic installation is 5/8", but many here among us think that's too little.

Brian

[Saint Toro]

Thanks for the advise Brian, I want to make sure it's strong enough, I don't want a mess later, maybe ceramic is the way to go. Looks like I've got some decisions to make

[Saint Toro]

OK.... after a lot of thought .... Ive decided to put 5/8 on top and put a transition theshold b/w the hd and tile.... another question is in my foyer, which i plan to do as well (hurry, before SHE adds another room ), it has 3/4 x 5 T&G pine on a diagonal as the subfloor (with 3/4 HD on top- which i plan to remove), can i put 1/2 over the T&G to get my 1 1/4 subfloor (this is at the end of the hall, on the other side of the beam) and then the same travertine or do i need to rip that up and replace it with ply? a little chunkier 2 x 8 on this side (old and measure at 2 1/4") 11 ft span
This site is super! Lots of good advise and food for thought. thanks again

[Brian in San Diego]

Mark,

If you use Ditra, according to Schluter that meets their minimum for that situation. I think you'd be o.k. but if you can spare the 1/8", I think I'd go with 5/8" there as well. I happen to really like the ditra product and I think it may help marginal situations where a backerboard may not. I would use Ditra instead of backerboard for your project. It's a bit more expensive but is far easier to install than backerboard. If your joists are true 2" x 8" with an 11' span you come up with L/645 if they are 2.5" x 8" you get L/806...the middle is L/726 so if they are "true" 2.25 X 8 then you should be good. I would make sure the planks are securely fastened to the joists with screws not nails, add my ply, ditra and tile. Go to the Liberry and check out the thread on Plywood, CDX etc. There's a link to a really good article in post #3 of that thread.

Brian

[Saint Toro]

thanks brian, i see your point, since these 2 floors meet (2x5/8" on one and 3/4" + 1/2" on the other) i thought this would make the two floors level. What can i do to make the transition between floors stable if i put 5/8" on all of it. I could take the T&G out and replace it with 5/8" ply? Its a bit more work, but would it be better? going to check out that thread (maybe it answers the quest for me)