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  1. #1
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    Default Joist or Just Blocks for Subfloor?

    I have ripped out my existing 100+ year old wood bathroom floor to the studs and will put in a ceramic floor. There is not a joist along one wall (next available joist runs under floor in adjacent room) Because of the construction of the home it is near impossible to properly run a new floor joist. Would blocks between the existing joists be enough to hold the subfloor and prevent tiles from cracking when stepped on? The span from the wall to the visible joist is 12" on center. The original joists are spaced 14.5" on center. -M
    Last edited by handygirl; 10-31-2007 at 07:57 AM. Reason: typo

  2. #2
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    Default Joist or Just Blocks for Subfloor?

    I have ripped out my existing 100+ year old wood bathroom floor to the studs and will put in a ceramic floor. There is not a joist along one wall (next available joist runs under floor in adjacent room) Because of the construction of the home it is near impossible to properly run a new floor joist. Would blocks between the existing joists be enough to hold the subfloor and prevent tiles from cracking when stepped on? The span from the wall to the visible joist is 12" on center. The original joists are spaced 14.5" on center. -M

  3. #3
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    Default Re: Joist or Just Blocks for Subfloor?

    Good luck getting an architect or engineer to stamp plans for a bathroom floor finish renovation.
    While the joist spacing is part of the equation, the size of the joists, span & loading will let you determine the deflection and that will tell you if the tile is likely to crack.
    Does the floor feel bouncy now or does jumping on it make it bounce? If not then picking up the edge of the subfloor with blocking is a good idea & should work. Use 3/4" plywood for subfloor with tile.
    Of course their may be more to it than I can tell, so use good judgement & common sense. A tile store, not a big box place, can be a good resourse for tile as well as information.

  4. #4
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    Default Re: Joist or Just Blocks for Subfloor?

    I think DW is right. It's sounds like you cut out the existing flooring and sub-floor to the wall and now you have a wall sitting on the cantilevered ends of the flooring going into the next room. That's a bigger problem than just blocking for cement board.
    Jack
    Be sure you live your life, because you are a long time dead.-Scottish Proverb

  5. #5
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    Default Re: Joist or Just Blocks for Subfloor?

    Quote Originally Posted by handygirl View Post
    The span from the wall to the visible joist is 12" on center. The original joists are spaced 14.5" on center. -M
    handygirl ....There seems to be some wild speculating going on.

    This is what I read into your post .... you removed the existing sub floor and found the joists spacing to 14.5 inches on center. The one floor joist in the area in question is 12 inches away from that wall.

    This left me wondering if the next joist you can't see is approximately 2-3 inches under the sole plate of that wall.

    The question I have is ... what is the distance from the joist that is 12 inches from the wall to the next joist you can't see?

  6. #6
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    Cool Re: Joist or Just Blocks for Subfloor?

    All of your suggestions were great! I am still undecided as to the approach to the mess I have made. But, here are some answers to your questions.

    "Is this a load bearing wall? Span? Return wall?"
    It is not load bearing. The room is small 5' x 6'. The long wall is in question.

    "Does the floor feel bouncy now or does jumping on it make it bounce?"
    The floor is very solid.

    "...and now you have a wall sitting on the cantilevered ends of the flooring going into the next room."
    Somewhat true, the studs dividing the rooms sit on the joist but the lathes and plaster on the bathroom wall do hand over that joise.

    " ...and found the joists spacing to 14.5 inches on center. The one floor joist in the area in question is 12 inches away from that wall."
    The floor joist in the bathroom is 12" from the wall and there is a 2.5" space from the bathroom wall to the next joist in the adjacent room.

    "This left me wondering if the next joist you can't see is approximately 2-3 inches under the sole plate of that wall."
    Yes

    "The question I have is ... what is the distance from the joist that is 12 inches from the wall to the next joist you can't see?"
    14.5"

  7. #7
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    Default Re: Joist or Just Blocks for Subfloor?

    I would put the blocking between the joist that is 12" from the wall and the joist that is just under the bathroom wall. Place the blocking 16" apart. Make sure you get the subfloor to the correct thickness as recommended by the tile mfg.

  8. #8
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    Default Re: Joist or Just Blocks for Sub floor?

    handygirl .... thanks for the information.

    It's pretty much as I thought... as a matter of fact that's exactly the size of the bathroom I'm currently working on .

    This is a very common situation and in no means should it require a structural engineer or architect.... unless you're putting in a 91 gallon cast iron soaker tub.

    The thing with plywood or OSB the strength also comes from proper fastening of the perimeter edges. You want to ensure to fasten these to a continuous solid surface. You could use blocking secured between the two joists but that doesn't allow for a solid continuous surface for securing the perimeter of the sub floor sheathing... unless you put blocking between the blocking then this will work nicely.

    Another suggestion would be to pad out the joist under the wall with vertical pieces of 2x4's and plywood spacers attached to that joist ..... spaced at say 14.5 inches or 16 inches. Then attach a full length of 2x6 or 2x8 (for example) to these spacers.... it's simply a nailer.
    What you will end up with is a joist ( nailer) that should be half under the bottom of the entire length of the wall and half protruding past. . This will provide a solid continuous fastening surface for the perimeter edge of the plywood and support for the sole plate of the wall.

    I'm guessing the tub may be placed along the 5 foot width outside wall in which case there wouldn't be a need to double anything since it will be the strongest part of the floor and the tub would be sitting on top of 2 or 3 joists anyways.... but it would never hurt anything to double them if you wish.

    The other consideration is you may have to install blocking along the edge of the other short wall ( possibly where the door is ?) since the plywood should have a solid continuous fastening edge there as well.

    Then once all that is done lay down tongue and groove plywood at least 3/4 thick and go crazy.

    Hope this helps.
    Last edited by canuk; 11-01-2007 at 08:29 AM.

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