Had to remove part of my subfloor, now I have NO idea what to do...please help!

Discussion in 'Shower & Bathtub Forum & Blog' started by amateurplumber1, Jul 25, 2014.

  1. amateurplumber1

    amateurplumber1 Member

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    Hey all...I am remodeling my shower and have run into a problem. The subfloor was rotted so I removed it and am adding a new subfloor. I bought the plywood, and planned to put a nailing edge on the left and right sides where the old plywood sticks out slightly to support the new plywood.

    HOWEVER, I am worried about the left and right walls. Since I've cut the plywood, I am worried that they dont have enough support. Underneath them is just an empty space; the joists to the left and right side of the left and right walls, respectively, are a few inches away. How can I support the walls better? Here is an image of what I'm talking about (I know the idiots cut the joist to fit the drain; I plan on sistering it).

    Thanks SO much!
  2. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

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    I'd install some blocking where I could, and then when installing the new subflooring, glue and screw a 3/4" ply cleat to the bottom of the existing subfloor sticking out, and to the new sheet, effectively joining them together as one piece. Use a good wood glue like TitebondII rather than construction adhesive, since it's easier to get a full, continuous layer. Construction adhesive works great in places like the top of a joist because you have some pretty concentrated clamping with the fasteners and the small surface, but not when you have a wider surface.
  3. johnfrwhipple

    johnfrwhipple Bathroom Design & Build - North Vancouver, B.C.

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    [​IMG]

    There is the picture of your floor.

    You are going to need to support those two walls left and right.

    Are the other other rooms getting renovated?
  4. amateurplumber1

    amateurplumber1 Member

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    Just the shower. Someone in another forum told me I could screw and glue some 2x6 pieces to the base of the frames of the walls and screw the new plywood into that and it would be good. But i dont know. I could remove the ceiling of the floor below and gain access to the joists. Then, with your guys' sage wisdom, I could add blocking to the joists. BUT, if I dont have to add blocking, I'd rather not!
  5. johnfrwhipple

    johnfrwhipple Bathroom Design & Build - North Vancouver, B.C.

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    What ya who told you that? Bad advice. (Let me guess... Someone on the John Bridge forum said that).

    A structural engineer would be looking for what the weight requirements are for those walls. If there is nothing special you would most likely be requested to put in 2"x4" or 2"x6" cross blocking between the joist spans. Most likely on 16" centres or under each wall stud.

    Those are 2"x10" floor joists I'm guessing.

    Net 9.25" - 5.5" (if you use a 2"x6" blocking) = 3.75"

    So if you reach in and screw a 2"x4" (which only measures 3.5") 1/4" above the lower ceilings drywall a 2"x6" should fit above that and support the subfloor. I would then drive in long 4" screws through the bottom plate and grab the 2"x6".

    They make 2"x4" and 2"x6" joist hangers. If you have can reach you can drive those in as well. Or use both.

    This new work only helps support the wall and does not give a new nailing edge on the perimeter. That needs to go in after the support work is done. The support for the perimeter should be all four sides.

    That P Trap looks tight to the floor joist and the through hole drilled looks like it is also very tight...
    Last edited: Jul 25, 2014
  6. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

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    Because those walls are not running across the joists, they are not load bearing walls (if they were, things would have started to sag already!). You want to emulate the continuous subflooring that was there before you cut it out. A decent width cleat (ply, not solid wood as that could split) underneath, glued and screwed (functionally laminating them together) to the existing, and new ply will be as strong as the original flooring. Any additional blocking you can put in just makes it stronger. A couple of rows of screws on each side of the joint along with a full coat of a good glue should work fine.
  7. nukeman

    nukeman Nuclear Engineer

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    Yeah. Those walls aren't carrying any loads at all. Only thing they are carrying is the weight of the sheetrock and the studs (minor deadload). You certainly don't need a structural engineer for non-load bearing walls.

    For the left and right walls, all you really need is something to screw the subfloor to (cleat or blocking). What you currently have is completely normal for a non-load bearing wall. They get placed where needed and often are not above a joist.
  8. amateurplumber1

    amateurplumber1 Member

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    Excellent, what a relief, thank you! Should I just go ahead and screw+glue the 2x6 I have cut in the correct dimensions to the existing plywood lip or to the actually frame of the walls?
  9. johnfrwhipple

    johnfrwhipple Bathroom Design & Build - North Vancouver, B.C.

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    What ???

    I would listen to my post. No offence Nukeman but that is not normal. Normal is for the plywood to span from floor joist to floor joist. What we have pictured above is a butcher job of floor prep.

    We do not know what type of shower this person is building or the stress of the floor movement on the waterproofing system.
    Last edited: Jul 26, 2014
  10. amateurplumber1

    amateurplumber1 Member

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    What does adding blocking actually involve? Do I just stick some wood in between the joists and screw it in with joist hangers or something?
  11. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

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    Yes, adding blocking is best done with joist hangers. I would prefer to use plywood as my cleats as it's less likely to split with a bunch of screws in it along a line. Dimensional lumber works good when you use it with the short side up, but not flat, as a cleat. If a joist is close enough, sometimes you can sister material onto the side of it to support an edge rather than hanging a new one in there. Another way you can do it is to put cleats on the sides of the joists so you can put a layer of plywood on them so that it is flush with the top of the joists, then install the new sheet, and anchor it to that, rather than trying to install cleats on the joint. It can be a major pain if you don't have access from below, to anchor the edge if your wall is in the middle of the joist bay.
  12. nukeman

    nukeman Nuclear Engineer

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    Of coarse it is. A non-load bearing wall can sit anywhere. The wall itself is simply a divider and serves no other purpose. It carries no load (other than it's own weight..hence the name). All you need in this case is support at the edge of the plywood patch to prevent deflection at the edge. This could be a simple cleat or some sort of blocking. It doesn't need to be anything special. Just needs to support the edge of the current pieces and support the edge of the patch (gives something to screw to and supports the edge).

    If the patch was cut to line up with joists, it would make things easier, but this still isn't an issue. He could put blocking perpendicular at 16" centers or could do a cleat parallel to those edges. Whatever is easier. It is just to support the cut edges to prevent deflection of the plywood at the edge.
  13. RedShoecounterbalance

    RedShoecounterbalance Active Member

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    I would consider the weight of the concrete shower pan, the tile, and 2 humans.

    Cover my ass and add cross blocking from joist to joist 2x6 or larger, then i would further block the seams of the entire cut out area.

    I doubt those are structural walls or carrying a load as there is simply a bottom plate over plywood not carrying thru to the floor beneath if im seeing correct


    but still lets plan ahead for weight and a smart build? Can you open up the drywall cieling from below to assist in blocking?

    As for the pipe thru the joist i suggest 3/4 plywood sisters crossgrain for strength and less weight ......double if you like glue & screw


    After all that double up the subfloor in the shower again crossgrain glue n screw . Use quality exp1 BC ply and kiln dried spf lumber

    Just my 2 cents
    Last edited: Jul 26, 2014
  14. amateurplumber1

    amateurplumber1 Member

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    To add blocking I literally just show a piece of 2x6 in there and screw it in? That's it? Anything I should know specifically?

    I'm actually not using a cement shower pan; I'm using a preformed kerdi foam pan.
  15. RedShoecounterbalance

    RedShoecounterbalance Active Member

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    Cross blocking will span between joists for one joist to the next and so on. Ideally you will use a palm nailer and simpson or hanging brackets

    The cowboy method is to glue and screw. You want to use exterior gradedeck screws and PL glue you will predrill your blockers in a toescrew fashion pointing up and in as to slightly pull blocking up as you tighten screws
  16. RedShoecounterbalance

    RedShoecounterbalance Active Member

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    Im typing on an iphone sorry! Ad blockers ever 16 inches and then add preimiter blockers at all seams of cut out subfloor area
  17. RedShoecounterbalance

    RedShoecounterbalance Active Member

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    You have created a weak link in the subfloor and all this blocking will re- strengthen it if you do a good clean supportive job of it.
  18. RedShoecounterbalance

    RedShoecounterbalance Active Member

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    B stands for new blocking!!! image.jpg
    johnfrwhipple likes this.
  19. johnfrwhipple

    johnfrwhipple Bathroom Design & Build - North Vancouver, B.C.

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    All the more reason to be careful. That Kerdi shower base is made from FOAM !!!

    Remember Kerdi requires non-modifed thin-set and this suffers from mortar fatigue more so than modified thin-sets. Any flex will be stressing those silly non-modified thin set seams... Scary.

    If memory serves me correctly I think after you prep your subfloor you need to make sure it's perfectly level as well. The Kerdi pan needs an absolutely perfect substrate - kind of like a lab setting.

    Take the time to do the blocking right. Snow Loads. Roofing Loads. Maintence Workers. Falling trees and branches. You never know when the ceiling or roof will be stressed. What is not sagging today might in three years if the conditions are just right.



    The trickiest blocking member will be the one that runs through the shower drain line. I would cut that out - do the blocking and then re-install the shower drain line.
  20. amateurplumber1

    amateurplumber1 Member

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    Man oh man...that is a LOT of blocking! Thanks for the pictures and advice. I'm not sure I'm up to this task, lol. If only I didn't have to add the blocking around the perimeter!
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