subfloor question [Archive] - Ceramic Tile Advice Forums - John Bridge Ceramic Tile


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04-24-2009, 05:14 PM
I have a laundry room that I want to tile. It's now linoleum. Below the laundry room is an unfinished basement. I can see from underneath that the plywood subfoor is 23/32" thick. I wanted to add .5" cement backer board to the floor but the floor level will be too high for the adjoining hardwood floor. Any suggestions on how to proceed?


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04-24-2009, 05:20 PM
Joists underneath are 24" oc, and are 16" deep.

04-24-2009, 05:32 PM
Welcome, and how about a first name to call you. Go to your "User CP (" and enter it so it appears on all your posts.

So, 16" tall joists probably means they're engineered, yes? If so, you'll have to find out the manufacturer and the size of the flange. This will help you to determine exactly what joist you have. Look for a stamp on the side of the joist too. Then you need to find the unsupported span of the joist. Then, you'll have to look up the specs of your specific joist and see if they're designed to support tile. I'd check the manufacturers website for the spec. As they are 16" tall, you may be fine, but you still need to verify.

Do this much and let us know how you made out.

Good luck:)

08-18-2012, 08:00 AM
I want to tile a 5.5' x 9' laundry room that is currently linoleum. The joists are 24" on center with a 23/32" subfloor. My plan is to add another .5" of plywood to increase the thickness of the subfloor. I then want to use a layer of Ditra to mount the tiles to. (I'm using ditra to keep the overall floor height to a min. If I use cement board, the height will be too high). Does anyone see a problem with my plan? I will use ceramic tile.

08-18-2012, 09:14 AM

The 5.5' lenth is the direction the plywood grain would need to go since that is the direction that is perpendicular to the joists. I'm hoping to use 1 piece of plywood to span this entire 5.5' length but I'll have to see where the subfloor joints are.

I'm not exatly clear what "perimeter joints" are. Is this something I need to be concerned with?

05-02-2013, 06:47 PM
The subfloor in my small laundry room is 23/32" thick (over 24" spaced joists). I need to add another 1/2" of ply wood so i can then add ditra and tile. I've read on other forums that i should just screw in the new plywood to the subfloor and not use adhesive. Comments?

05-02-2013, 07:50 PM
Welcome again, wupot. :)

And let me ask again that you put a first name in your permanent signature line for us to use.

I combined your previous threads here on the presumption that you have only one laundry room floor to tile and it's just been delayed for a while and so folks can see what you're working on and what's been previously asked and answered.

Not sure what I can add to what's been previously posted, but here's a good article on what I think is the best way to install the second layer of plywood subflooring. I recommend you follow the suggestions to the extent applicable to your floor. The authors do not recommend gluing the subfloor layers.

My opinion; worth price charged.

05-05-2013, 06:16 PM
I just realized i can't add .5" of ply. I need to add 3/8" otherwise the floor is too high. According to ditra this the bare min.

I can't seem to find any markings on the joists. They span 16' and are 16" deep and 4" wide, 24" oc. What concerns me a bit as to if my install will be successful or not is that a bathroom on the other side of the house has tile. There are additional joists in this one, small area and the distance between joists is about 12" or so. Everywhere else is 24" including the area where i want to tile.