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pinkertonpv 02-02-2009 04:12 PM

Ceramic tile over subfloor in Kitchen
I am remodeling my kitchen/dining room and among many other things, want to put down ceramic tile. The kitchen floor is 21' by 11'9"; 205 SF; supported by 2x8 joists running the short span 11'9" long. They are resting on outside foundation wall and on the inside a ledger attached to a double 2x10 girder. The girder is supported by concrete block columns 7' oc. The subfloor is 1/2 " plywood covered with particle board. The particle bd and plywood will be replaced with 3/4 T/G OSB. I plan on transitioning from the tile to laminate flooring in dining room and hallway.
1. Will the supports/foundation handle the load of the Tile & thinset and subflooring.?
2. Can I install the tile over the OSB or should I cover the OSB with additional plywood or backer bd?
3. Should I tile the entire floor and put cabinets over the tile? Planning on installing new cabinets, island and granite counter top. Been told by store rep cannot remove granite counter top if dish washer or other appliances usually mounted on subfloor need to be replaced. He recommended installing tile floor first and then cabinets, dish washer, etc. The I can slide out appliances.

Any comments or recommendations would be helpful and very much appreciated.

Floorwizard 02-02-2009 04:43 PM

If your going to put down new 3/4 OSB subfloor then it would be wise to suppliment with a backerboard.
You could put the tile under the cabs, but that would be at least 50 sq ft of unseen tile for no good reason...sounds like a waste of money really.
The only way to install directly on wood substrate is if the total thickness is 1 1/4 and is completely plywood only. Even then I would add something to help with movement.

angus242 02-02-2009 07:46 PM

How far are the joists spaced from each other? That will help determine if your joists are strong enough.

You should use an exterior grade T&G plywood instead of OSB. You're on the low end of what might be an acceptable subfloor for tiling. I'd consider adding maybe another layer of 5/8" exterior grade plywood over the T&G.

You need to use some kind of underlayment for the tile. Cement backer board is one option. A tile membrane is another. Ditra is an excellent product. Easier to install than cement board although it's a bit more expensive. Well worth it in my opinion.

I like to tile under cabinets.

JazMan 02-02-2009 09:36 PM

Let's start with the joists. You say the span and the room width ia 11'9". Are you sure? Did you measure the span from underneath? Please double check. Please answer Angus's question about the joists' spacing. Would also be nice to know the species and grade of those wimpy 2x8 joists.

I'm not clear how the joists are attached to this girder. I bet there's some give in the girder, no? You will have to reinforce that floor because of the island if everything else is OK, and I don't know yet.

1. 3/4" t&g sub is generally ok, more plywood is better. Don't know about the joists yet. 2x8 joists are too weak in most cases if the span is even a bit less than you stated. Add the island, no good.

2. You can not install tile direct to any OSB.

3. I prefer installing the tilles first, you still don't have to cover the entire floor though. If you install the cabinets first, they need to be shimed up anyway, so the DW is not really an issue.


pinkertonpv 02-03-2009 11:22 AM

2 Attachment(s)
I appreciate you guys responding.
1. Joists spacing is 16 inches oc. Meant to include in original post.
2. Joists are 119 from outside concrete block foundation to inside support girder. Measured from inside the crawl space. Joists are attached to the girder by a ledger board. You can see it in the pictures
3. Dont know species or grade of wood. Nothing written on joists or ledger, but wood looks like pine or fir. House is 35 years old and located in N. Alabama.
4. Will use exterior plywood instead of OSB and another layer on top of that. Will use ditra if necessary. From the web site it sounds like excellent stuff. May have pros put down tile once I get the sub floor in and all the kitchen prework done.
5. I can add several sister joists where the Island will go. Or will an intermediate support be necessary? The Island will actually be L shaped and run along the girder for 5 feet and turn 90 degrees toward the kitchen door for 6 feet. You can see the door in the picture. The wall in the picture will be replaced by a beam supported by a post. The edge of the wall is the outside edge of the island.

JazMan 02-03-2009 08:31 PM

1. OK, 16" o.c. is standard.

2. A span of 11'9" is too much for tile. You need to either sister or install a supporting bean under across those joists. Make sure they all touch, maybe steel I-beam? I think I'd rather sister if there's any obstructions at all.

3. Well OK, you're gonna sister or put in a beam so doesn't matter.

4. Make sure you do NOT buy pressure treated "outdoor" plywood. Get 3/4" subfloor grade plywood, it'll say something like "exposure 1". The underlayment can be thinner, like 3/8" or 1/2" or thicker if you need the height. The more the better. Ditra is a good idea, better than cement board and only adds 1/8", so you can go with thicker plywood.

5. Sounds good cuz you've already done #2. :thumbsup:


pinkertonpv 02-03-2009 09:13 PM

Jazman; Thanks for the info. I don't think I can add a girder or steel beam under the joists. the run would be over 22' and I would need several concrete block columns. Sistering sounds better, but will I need to sister every joist or can I just sister every other joist. I will be adding the two layers of plywood. Obviously I need to sister joists and increase the strength under the island.

JazMan 02-03-2009 09:42 PM

Adding plywood will not improve your joists' deflection. You should sister every joist because 1. of the island and 2. the joists are overspanned which affects the entire area,


angus242 02-03-2009 11:25 PM

Plywood only adds support to the areas between the joists. You still need to address the over-spanned joists themselves.

Follow Jaz's advice and you're good to go!

Stevonator 12-31-2012 09:45 PM

Ok....gonna revive an ANCIENT thread here because it just happens to be exactly where I am at with one small twist. Kitchen is 20 x 24 with 2x8 joists 16 oc. Only mine are DOUBLE SPANNED the whole 24 feet! (don't look at me...I inherited it that It's also framed about an inch too high as well, basically the top of the joists are even with the hardwood floors in the adjoining room. The joists rest on a plate on the concrete block foundation.This isn't even the whole's a mess. I have the subfloor removed and would like to lower the floor level and go with tile. Any thoughts on achieving a satisfactory floor stiffness at a 6 inch joist depth and at what span? TIA

oh'mike 01-01-2013 06:24 AM

Steve---I doubt if many members want to read the entire old thread in order to help you---please consider opening a new thread--Mike---

kt82 01-12-2013 12:40 PM

why do you archive old threads?

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