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  1. #1
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    Default questions on replacing a subfloor

    Hello

    Apologies in advance for the long-winded post...

    I'm a novice DIY'er renovating the upstairs of my house. It was previously finished with 2 bedrooms and a bathroom, but for various reasons, I've demolished all the framing, plumbing, electrical, etc and will basically be starting fresh. So presently, I have one large open space from one gable end to the other.

    The current subfloor is 1/2" plywood, and is sagging in several areas due to leaks in the bathroom and exterior siding (which I've since fixed). I've removed all of it - right up to the sole plate of the exterior walls - and have ordered 3/4" T&G OSB Sturdi-Floor as a replacement.

    However, I'd like some feedback on my plan to install the new subfloor where it meets the exterior walls. Where the floor joists are parallel to the outside walls, I'm planning on installing full-height blocking every 12" between the rim joist and adjacent joist, and then screwing both the subfloor and exterior wall sole plate to the blocking. Where the outside wall is perpendicular, I didn't plan on installing any blocking. Is it necessary? If so, is it just supporting the subfloor panel edge, or do I need to screw the subfloor/sole plate into it too?

    If it makes a difference, the joists are 2x8, 16" oc, and an unsupported span of 8.5' - 11' 10". I plan on installing a 1/2" BC plywood underlay on top, and then tile in the bathroom, and 5/8" hardwood in the bedrooms. The upstairs has a fully dormered back wall, connected by collar ties to the front rafters. Part of my concern is that the back wall is out of plumb by about 2.5" over a 7' height (!). My local inspector says this is due to the poor construction technique used when my house was build, and is just cosmetic (i.e. the house isn't going to fall down). However, I'm not sure if removing the subfloor somehow removed part of the support for the back wall...crazy thought?

    Thanks for any advice/feedback
    Last edited by Wm_Boston; 09-23-2007 at 09:11 PM.

  2. #2
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    Default Re: questions on replacing a subfloor

    No floor blocking needed...I use flooring screws rather than nails though to fasten my subfloors down http://www.mcfeelys.com/product/0820...T20-Star-Drive
    I also put a bead of PL 400 or PL Premium glue on each joist before I drop it into place http://www.stickwithpl.com/Products/...PLProductID=14
    Far as the wall out of plumb its no saftey problem but if it bothers you you can always fir out the entire wall before you rock it...heh heh...didn't think it'd bother you...lol.

    Any floor you tile you need a minimum of 1 1/4" of wood subfloor to minimize any deflection in the floor then use your CBU (cement boards) or Ditra.http://www.schluter.co.uk/produkt.as...ml&pg=funktion
    HAve fun : )
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  3. #3
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    Default Re: questions on replacing a subfloor

    Hello

    Thank you for the reply. To clarify, when you say "no blocking needed", that's where the outside wall is perpendicular to the joists, right? I'm assuming that where they're parallel, the blocking every 12" would be adequate. I'm not sure why I had it in my mind that the new subfloor somehow had to be "more connected" to the existing structure.

    I'll make sure to glue and screw the new subfloor down. For the tile, I did plan on using Ditra; the combined thickness of the OSB subfloor and BC underlayment will just get me to the minimum thickness.

    And as far as the out of plumb wall, it's something I'll learn to live with...I was more concerned with a possible structural problem.

    Thanks again for the feedback.
    Last edited by Unregistered; 09-23-2007 at 10:25 PM.

  4. #4
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    Default Re: questions on replacing a subfloor

    Quote Originally Posted by Unregistered View Post
    Hello

    Thank you for the reply. To clarify, when you say "no blocking needed", that's where the outside wall is perpendicular to the joists, right? I'm assuming that where they're parallel, the blocking every 12" would be adequate. I'm not sure why I had it in my mind that the new subfloor somehow had to be "more connected" to the existing structure..
    Your floor joists are attached to your outside wall plates...key word "attached". Your subfloor doesn't really make it "more" attached.

    I love products like Advantech subfloor and the like. amazing stuff. I did that through out all the additions in my house. Its hardly any more money than ply and is far superior. Just sucks cuttin' the stuff!
    http://www.huberwood.com/main.aspx?p...antechflooring
    I used 3/4" T&G Advantech and dbl 3/4" where I tiled in bathrooms.
    I used PL Premium glue and screws. Squeek free and solid as a rock!
    There's also a little bit of a learning curve to get the T&G together nicely. Use a piece of scrap from the groove side to slide onto each new piece on the tongue and use a sledge to wack it into place. Its important on any T&G floor not to hit the tongue or the groove or you'll F it up and the next piece won't slide in nice and throw the whole thing off!!
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  5. #5
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    Jun 2007
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    Default Re: questions on replacing a subfloor

    Wm_Boston ,
    If I understand you correctly you are concerned about supporting the edge of the sub floor next to the wall running parallel to the joists. If that is what you mean, you don't need blocking just nail a 2x4 to the the framing parallel and level with the floor joists this will be more than adequate to support the edge of the flooring because it will be nailed every 16".
    Jack
    Be sure you live your life, because you are a long time dead.-Scottish Proverb

  6. #6
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    Default Re: questions on replacing a subfloor

    ...just nail a 2x4 to the the framing parallel and level with the floor joists
    Hello Jack

    Thanks for the suggestion, but I'm a little unclear how that would work. I had used a toe-kick saw to cut flush with the sole plate of the outside walls. The sole plate is 3.5" wide, and the rim joist takes up 1.5" of that width. I would have to nail two additional 2x4's in order to have enough thickness to extend past the sole plate and provide a ledge for the new subfloor to sit on. Or - if I nailed the 2x4 to the joist adjacent to the rim joist - that would mean there's still 12.5" of the subfloor with no support, since the joists are 16" o.c.


    In my original post, I was unclear whether any blocking was needed to support the edge of the sub floor next to the outside wall running perpendicular to the joists. AndyBuildz suggested that none was necessary.

    Thanks

  7. #7
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    Default Re: questions on replacing a subfloor

    ohhhhhh...now I get whatcha talking about. I take back part of my answer and you're right to add what you're calling blocking. You're talking about needing a nailer so the subfloor doesn't float at the end...right?
    Blocking is the right thing to do being you can't get a 2x in there without using two of em'. In that case blocking would be easier. If you have a hard time nailing to the rim joist cause of elbow room...pre drill some pilot holes in the blocks on that end and shoot screws through it..a dab of PL Premium wouldn't hurt either if you think you need it.
    Be sure you place blocks where the seams of the new subfloor end up too.
    Sorry if I misunderstood you before...Jack helped clear that up for me with his answer.
    OK,,,gotta get back up on the roof....
    Last edited by andybuildz; 09-24-2007 at 09:59 AM. Reason: spelling
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  8. #8
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    Default Re: questions on replacing a subfloor

    Hello again

    AndyBuildz, thanks for the reply. Yes, by blocking I was referring to some kind of support for the subfloor edge where it meets the outside walls.

    Do you mind if I summarize? I'd like to make sure that I've understood correctly.

    1. When the new subfloor is parallel to the outside wall, install the full-height blocking between the rim joist and adjacent joist every 12" AND under every seam. I'll screw the new subfloor into the blocking...do I need to screw through the sole plate into the blocking as well?

    2. When the new subfloor is perpendicular to the outside wall...any blocking necessary? If so, should I screw both the new subfloor and the sole plate into it?

    3. Out of plumb back wall...I've understood the replies to be that this isn't a problem, and doesn't need to be addressed.

    The reason I'm asking specifcally about screwing the outside wall sole plates to the blocking relates to my earlier comment about "connecting" the new subfloor to the existing framing. I don't know if it's necessary to screw both the new subfloor and existing wall framing to a common piece (the blocking).

    Thanks again for the advice.

  9. #9
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    Sep 2007
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    Default Re: questions on replacing a subfloor

    Bump...

    Hello

    Just wanted to see if anyone could provide feedback on my last post. I'd like to make sure that I've understood things correctly, plus clear up a few additional questions.

    Thanks in advance

  10. #10
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    Default Re: questions on replacing a subfloor

    You can screw the blocking into the sole..you don't have to screw from the SP into the blocking if thats what you're wondering..and if you use some PL Premium that'd help give it more holding power. Its just a nailer. No real intense bearing weight will be on it.

    The PL Premium gle is some incredably strong stuff so it you glue up the plate and the floor joists besides screws that thang ain't goin' anywhere!
    God forbid you ever need to pull a sheet up...lol .
    Last edited by andybuildz; 09-26-2007 at 11:56 PM. Reason: felt like it...ok?
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