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-   -   Need advice on subfloor (https://www.johnbridge.com/vbulletin/showthread.php?t=81297)

*lynn* 01-30-2010 06:36 PM

Need advice on subfloor
I need some expert's opinions here because my husband has about had it with my "little" project and I need to finish it.
I little background. The house was built in 1924 and the living room consists of the original room plus a front porch that was closed in and made part of the living room. I would guess this was done in the 1960's or 70's. The original floor of the porch was built slanting downward toward the outside. When it was closed in joists were fashioned out of 2x6's cut at and angle to sort of match the floor plus compensate for the various irregularities of and old porch floor. They were toe nailed onto the porch floor and tied to the joists of the house at the edge where it meets the house. Two layers of 1/2 inch plywood was put on this to make it level with the original oak flooring in the living room and then carpet put over all of it. I couldn't take the carpet anymore so I pulled up the floor on the porch section. The original porch floor was in good condition. On most of the floor I cut the joists to make them 3/4 in lower so I could put the subfloor back and then oak strips to make it match the original living room. By now you are probably wondering where the tile question comes in, but I'm almost there ;) In the corner on the old porch area where the front door is, the bottom layer of the plywood is under the door frame and I couldn't see a good way of getting it out so I left the joists and bottom plywood alone in that area thinking I wanted tile in front of the door anyway. I got 12x12 slate to put there thinking it was sturdy and would hide the dirt well. I'm trying to figure out what to do for subflooring. Right now there is the one layer of 1/2 in plywood (which I can't get out short of taking the door out, which needs to be replaced anyway, but that is a summer project). I tried to use the deflecto but didn't know how joists that are resting on a solid surface count. The span is 6 to 7 ft and is 3 to 4 ft wide. I now realize that the slate is going to end up higher than the oak so will need a reducer.
Thank you if you made it this far and for any help, Lynn.

p.s. one more question that is off topic a little. I have read on here that when putting on the second layer of plywood to avoid the joists, is this true under wood flooring also?

Brian in San Diego 01-30-2010 08:05 PM


Welcome to the forum! All I could think of when reading your plight was Oliver Hardy saying to Stanley "Well, here's another fine mess you've gotten me into." I don't know if there is any real way to advise you on how to do your entry tile project. I would scrap the idea of stone and use a porcelain look-a-like if it were me.

You say the joists are laying on the original porch floor but that floor is over joists, right? You would have to know what size they were and their span and spacing and those numbers would have to be plugged into the deflecto. The other problem is the 1/2" plywood. What grade is it? Is it exterior? Is it CC or better or something like CDX sheathing. You have too many variables for us to give you a definitive answer on how to proceed.

Slate is not sturdy by any stretch of the imagination. It is brittle and tends to splay over time. Your best bet would be to lay some Ditra over what you have and tile it with a porcelain tile that looks like slate and cross your fingers. The structure is not suitable for a tile installation of any type... and especially not stone. Sorry.


*lynn* 01-30-2010 08:45 PM

Brian, thank you so much for your input. I am so glad to know the slate is not a good idea now rather than when it self destructs in 3 months!

Unfortunately the area is under the porch is not visible. We were actually under there a couple of summers ago redoing the footings and supports (got to love an old house) but did not think to measure the joists. The original joists in the rest of the house are 2x8 with 16 inch spacing so the porch ones may be the same. I can't find a mark on the pieces of plywood that are remaining. Most of the stuff I removed is marked exterior C-D, but a couple pieces are AC. I assume the pieces down are probably CD but who knows.

The slate is going right back to the store. If I were to brave using the tile would you recommend putting more plywood down before the datri?

Sounds like maybe I should put something down like laminate in a stone pattern (hopefully cheap)for now and maybe do a combine door/tile project in the future. If at that point I was to lower the joists is there a thickness of subfloor that would make tiles doable considering everything is based on the old porch floor or should I scrap the tile idea all together?
I guess I could always put the oak all the way to the door and invest in a heavy duty entry rug to protect it.
Once again thanks for helping me figure this out now rather than be sorry later.

*lynn* 02-01-2010 07:04 AM

Well I decided to just put laminate in front of the door for now to keep the peace.

Eventually I would still like tile there and hoping that can be combined with replacing the door. If I can verify the joists under the porch are 2x8 with 16oc then using deflecto indicates that is an okay base. Then I could put down a good new subfloor and ditra followed by tiles correct?
thanks, Lynn

Brian in San Diego 02-01-2010 07:40 AM


Without the exact particulars as to what is going on underneath the old porch floor it would be difficult to give a definitive answer but I think your chances of success would be greater than attempting to set over the existing 1/2".

All plywood in a tile installation "sandwich" needs to have a face grade no less than "C" so AD is a "no-no". When you decide to go forward with the project please post to this thread to refresh our memories. You can bookmark it or copy the URL or just remember your user name and password and look it up that way.



bbcamp 02-01-2010 07:42 AM

That's a lot of "ifs," Lynn. Keep in mind that porches are oftren designed to a lighter load rating or higher deflection allowable, so beefing up the joists may be required. However, there are ways to do this, so if you want tile in the room, you can certainly have it.

*lynn* 02-01-2010 08:22 AM

Brian and Bob, thanks for all the help and heading off a slate disaster. When the time comes to reconsider tile there I will do some investigation and post back with specifics. I think we may have reinforced some of the joists when we were under the porch before but can't remember for sure. If the joists are okay, once the door is out it would be "easy" to get the crappy plywood out and start over with that......
Thanks again, Lynn

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