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Bathroom subflooring material

renosteinke | Posted in Construction Techniques on August 29, 2011 03:27am

I need to replace the floor in my bathroom. I am following on an incomplete / botched job.

What is the material of choice? Floor has lumber joists; spacing is not yet known, but I expect to find them 16-20″ OC.

Apart from the usual ‘sheet’ goods, would anyone consider using ordinary lumber,  tongue & groove lumber , pressure treated lumber, or any other ‘board’ material? I am thinking it might be easier to deal with the various notches, etc., if I’m putting this in one board at a time. It would also make working in tight places a lot easier.

I also note that the most common subfloor materials are nominal 3/4″. Does this suggest that nominal 1″ lumber would be strong enough?

Would one install this at a right angle to the joists, or at a bias? Older floors and waals I have seen seemed to have the boards run at 45 degrees to the framing for some reason?

Finally, is is the practice to treat the subflooring – especially in the area of the toilet – in any manner so as to meke it less suscepatble to water damage if/when the toilet seal leaks again?

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  1. DaveRicheson | Aug 29, 2011 04:42pm | #1

    finish floor?

    3/4" Advantec would be my choice, followed by cement backer board if a tile floor is going in. If the joist spacing is greater than 16" oc, you may want to either add an addtional layer of 1/4" underlayment grade  osb, with all the joints staggered off the first layer joints. You only need that if you are going to finish with a tile floor.

    Sheet goods need not go in as one large piece if you have pipes, corners and such to cut around. Just be sure to cut any smaller sections so that they break on a joist. Glue and screw it down.

    As far as the toilet eventually leaking, it sounds like something else is amiss. A properly installed closet flang and blocking should never leak. Many times leaks occurr in home with old CI waste lines because it was not properly supported beneath the floor or the strapping that was there failed. The old pipe does not support the toilet, but if left unsupported itself, can add a lot of weight pulling down on the flang and surrounding floor causing it to eventually sag and seperate the seal form the bottom of the toilet.

  2. calvin | Aug 29, 2011 07:21pm | #2

    Reno

    I would use advantech or reg. 3/4 sheeting-ext. glue. 

    I don't know why exactly, but the diag. board runs may have been to resist racking esp. in balloon framing.  On the angle expands the supported length, not good-too much flex even when tongue and groove or shiplap are used.

    To easy it up on you for the cutting of the sheet goods, lay a line where you want the long edge to land (48" or less from a long wall.   Take rosin paper, plain or red, or some protection paper or meat wrapping paper..............whatever.  Tape that down to that line and run from wall to wall (no need to be too close, leave a gap if it makes it easier.  You don't need a continuous tape, just pcs to hold it in place.  Fill in the remaining long edge with another strip of paper (to get your 48" wide.  Again, no big deal if it runs off line with anything.  Tape that to the other paper-good.

    After it's down, take your framing square (or other known width straight edge) and lay that tight along the walls and obstructions, drawing a pencil line along the other edge - on the paper.  Go all around the paper's perimeter (except that long edge line).  Pull the paper up, register your long edge on the plywood sheet, and tape it to the ply.  Using that same straight edge, register it to the lines you drew and draw a line on the plywood.  Cut to that line-it'll fit like a glove.

    Proceed to the rest of the room (but stagger your end joints on different joists) with the same method if you need to, or use your now good edge on that sheet to measure off of-a framing square-drywall square will keep your measurements square to that sheet.

    You can use this method on your underlay of choice and finish material too if sheet vinyl.

    What?  no flooring down at all, just joists?  Run a line down the center of the joist that isn't more than 8' away from a wall.  Square off that and continue that as a line that crosses the joists.  Now you've got two layout lines to measure off of that are square to each other.  Take square measurements from those and you will be pretty darn close to all the cutout jogs etc.

  3. DanH | Aug 29, 2011 10:25pm | #3

    You don't say what you intend to use for your finished floor.  That makes a lot of difference.

  4. renosteinke | Aug 30, 2011 11:10am | #4

    Thanks for the replies so far ....

    The bath is poorly laid out, so there is a major re-do in the works ... perhaps in a year or so. In the meantime, the existing floor is rotted completely through -finish flooor removed and only subfloor present- in several places. A section around the toilet had already been repaired, but holes and soft spots remain along the tub and next to the vanity cabinet. I plan to rip it all out and get a solid floor. It looks as if I might have to pull the tub to do this.

    That tub issue is part of my reason for asking about using boards, rather than sheet goods. I just might be able to get under the tub without pulling it .... we'll see.

    In other words, this work is sort of 'temporary,' in that the remodel will result in -eventually- a completely different bathroom layout. I'm just replacing the floor as it is, with a view of doing it over in a year or two. Therefore, I plan to just lay some vinyl for now. I'll worry about the 'real' floor later. (Remember, the new layout will require the subfloor to be redone then).

    As for the wax seal / closet flange lasting forever, etc.... I beg to differ. I have seen far too many bathroom floors rot out as the result of them leaking. Whatever the cause may have been, I personally see a need to plan for this leakage. Call it a contingency plan for Murphy's law.

    One thing I've learned is that drywall screws are not appropriate for this work. Every screw head has lost it's recess to rust & crud; it looks like I'll have to get the floor up the 'hard way,' cutting the floor into pieces and prying them up. What fun. I can only hope that the joists are not also rotted. Afterwards, i get to sift the crawl space for sawdust, and other 'termite bait.' Oh Well! Wasn't planning on doing much this winter anyway :)

    1. calvin | Aug 30, 2011 08:01pm | #5

      Get some sacrificial visqueen down in the crawl

      or use house wrap-dispose of the crud, rather than clean it up later.

      For a temp solution, that you'll underlay for the vinyl, use whatever you feel like to patch the subfloor.

      Toilets that leak are installed wrong from the beginning, installed wrong as a result of a remodel, or the drain systems have failed.  There's no reason a toilet setting shouldn't last for damn near ever.  Movement kills it as does pulling and not replacing the wax ring.  Really, there's no excuse for a poor job that you don't see until too late.  Done right, it'll outlast you.

      If you're still not convinced, cut your sub circle for the pipe, slather on a good caulk sealant on that cut, top/edge and bottom.  Any leak now will not get sucked in the plys.  Even a poor job of setting will last.  There's no warning when a crawl is below.

      1. DaveRicheson | Sep 01, 2011 06:20am | #6

        Good

        You nailed it. Movement is what causes leaks.

        We have about 100 wall hung toilets in the commercial office building where I work. The back mounting/piping is substantial, but the bolt exposure is crucial. These things are rated for over 500 lbs. of loading because the toilet is like a cantilevered structure with the bearing on the bolts and inner wall pipe flang. Over the years these things get "butt slammed" by some really huge behinds. the only ones we hav ever had seal leaks develope in where one where the support  bolts where not exactly correct for exposure and allowed the toilet to move a little. The movement was so small that it is all but undetectable. I'm 155 lbs. and when I stand on the outside rim of a toilet we couldn't find any movement in the troublesome units. But you get a 250-300 pound body setting on one and it would rock and pull enough to tear the glued on foam seal loose from the flang.

        Same thing occurrs with a floor mounted toilets. Any movement of the toilet on the flang will eventually cause the seal to squish out or pull apart and result in a leak. I buy plastic toilet wedge shims at the supply house to make sure there is no movement in the toilet once it it is firmly seated and set on the flang. They are ribbed so they won't back out and are easily cut flush to the outside edge of the toilet, They won't move, won't rot  or shrink over the years of use and are easily hidden by a very small bead of caulk around the toilet base.

        1. DanH | Sep 01, 2011 07:05am | #7

          Further, a standard floor toilet shouldn't leak (much) even absent the wax ring.  The ring is there primarily as a gas seal, and the "aim" of the toilet horn should be good enough to "shoot" the waste directly into the pipe (which should not back up).

          When you get a lot of leakage it's likely that either the waste pipe is partially clogged, or the toilet has shifted enough that the "aim" is off.

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