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  1. #1
    Join Date
    Aug 2014
    Location
    Southern Ontario, Canada
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    Default Clueless new homeowners, conflicting advice: hardwood over plank subfloor

    Hello everyone!

    My partner and I are new to this home owning business, and really have no idea what we're doing!

    Our subfloor is made of 1" x 5" pine boards installed at a 45 degree angle over the joists, which are 16" oc. There is about 1/4" between each board. We have purchased hard maple plank flooring, tongue and groove, 4 1/4 wide, 3/4" thick to be installed. The floor has been in the area where it is to be installed for over a week now, so it should be good to go. There is pre-existing 3/8" thick by 1 3/4 wide" oak flooring in the living room and bedrooms.

    My question is this: can we install the new hardwood directly over the plank subfloor? If we need to put down 1/2" plywood, as some threads suggest, the new floor will be 1 1/4" taller than the existing flooring. At this point in time, we have no money to tear out the old floors to make everything level (I've just been accepted into school, so there will be no income coming in from my side, and the rest of the house needs pretty much everything done to it as well).

    The subfloor planks are in great shape with no evidence of water damage. We used 2 1/2" deck screws to further attach the planks to the joists. There is some mild deflection in some of the boards in the high traffic areas when we step between the joists, and a few small areas where the floor is not perfectly level. We live in southern Ontario, Canada, so we get all kinds of different weather (not sure if that matters).

    What should we do?

    Also, what is recommended for underlayment? We would prefer to not use anything that contains asphalt.

    Please help!

  2. #2
    Join Date
    Jun 2007
    Location
    Fayette County, Ohio
    Posts
    5,844

    Default Re: Clueless new homeowners, conflicting advice: hardwood over plank subfloor

    Yes you can install the flooring on the plank subfloor, it has been done that way for a long time. The only problem is that you may hit a gap when driving the flooring nails. You can us Resin Paper as an underlayment instead of 15 lb felt. You staple the resin paper down overlapping it about 6 inches.

    Jack
    Be sure you live your life, because you are a long time dead.-Scottish Proverb

  3. #3
    Join Date
    Jul 2010
    Location
    SoCal
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    6,762

    Default Re: Clueless new homeowners, conflicting advice: hardwood over plank subfloor

    Before you start, find out a way to fix the deflection, since you will load up the weight of the new floor.

    So how do you figure that? go to johnbridgeforum.com and find the formula to determine allowable deflection.

  4. #4
    Join Date
    Aug 2014
    Location
    Southern Ontario, Canada
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    6

    Default Re: Clueless new homeowners, conflicting advice: hardwood over plank subfloor

    Yay, thank-you JLMCDANIEL, that was just what I wanted to hear

    Thanks for the tip, dj1, I'm checking out that forum now.

  5. #5
    Join Date
    Aug 2014
    Location
    Southern Ontario, Canada
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    6

    Default Re: Clueless new homeowners, conflicting advice: hardwood over plank subfloor

    Quote Originally Posted by dj1 View Post
    Before you start, find out a way to fix the deflection, since you will load up the weight of the new floor.

    So how do you figure that? go to johnbridgeforum.com and find the formula to determine allowable deflection.

    The formula I found was for tile, not hardwood. Is there another, or is the number somehow transferable?

    Thanks!

  6. #6
    Join Date
    Jun 2007
    Location
    Fayette County, Ohio
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    5,844

    Default Re: Clueless new homeowners, conflicting advice: hardwood over plank subfloor

    I would lay a piece of the new flooring over the area and see if it deflects. You might be surprised.

    Jack
    Be sure you live your life, because you are a long time dead.-Scottish Proverb

  7. #7
    Join Date
    May 2008
    Location
    Pacific Northwet
    Posts
    1,675

    Default Re: Clueless new homeowners, conflicting advice: hardwood over plank subfloor

    Quote Originally Posted by JLMCDANIEL View Post
    I would lay a piece of the new flooring over the area and see if it deflects. You might be surprised.
    Bear in mind that a single, loose board will deflect more than several boards put together and fastened in place. The tounge-and-groove design will transfer some load to adjacent boards, reducing the deflection. Also, fasteners will add some measure of rigidity: as the two layers (finish floor and subfloor) deflect, the finish floor will push outward on the fasteners, while the subfloor will pull inward. The opposing forces will resist deflection. It's not much resistance, but it is some.

    It's good that the OP's subfloor planks are laid on the diagonal. While there isn't much chance of racking on the floor, it does mean that the finish floor can be laid either along either the length or the width of the room.
    The "Senior Member" designation under my name doesn't mean I know a lot, it just means I talk a lot.I've been a DIYer since I was 12 (thanks, Dad!). I have read several books on various home improvement topics. I do not have any current code books I can refer to. I was an apprentice plumber for two years.

  8. #8
    Join Date
    Dec 2010
    Location
    Houston Texas
    Posts
    2,969

    Default Re: Clueless new homeowners, conflicting advice: hardwood over plank subfloor

    You can use the deflecto - later on the JB Forum to get a deflection number. What number you need will be determined by your local building authority. Usually that is L360 for normal residential home construction be it carpeting, linoleum, or hardwoods. But I don't know for sure, since I'm 2000 miles away.

  9. #9
    Join Date
    Aug 2014
    Location
    Southern Ontario, Canada
    Posts
    6

    Default Re: Clueless new homeowners, conflicting advice: hardwood over plank subfloor

    Thanks for all the comments!

    We're going to beef up the subfloor from below to help fix the deflection. It only seems to be noticeable in 2 spots- pretty amazed at how well this subfloor has held up (house was built in the 50s and never maintained).

    We wanted to make sure that the floor was flat enough before we put down the hardwood. I used string and made lines roughly where the boards would go. We found a noticeable slant towards the stairs in the whole house, but the slant is even (i.e. there are very few high spots or low spots, the drop is consistent along the floor. At its worst (closest to the stairs), the drop is 1/2", but it's usually closer to 1/4".

    My question: If the drop is consistent, do we need to put in something to make it flat? If so, what should we use? I've heard of the shingle method, but I'd like to avoid using asphalt stuff under the floor. Can we use cedar shims? We have a bunch of those. I've heard not so great things about SLC - thoughts on that? I feel that it would fall down between the slats in our subfloor.

    Thank-you in advance!

    P.S.
    We've had a structural engineer in to look at the house recently. She's not concerned with the slant, although if we want to remove walls we need to put in a new beam.

  10. #10
    Join Date
    Dec 2010
    Location
    Houston Texas
    Posts
    2,969

    Default Re: Clueless new homeowners, conflicting advice: hardwood over plank subfloor

    Floors like flat. Level is another story.

    If you want to make everything level, that's a serious call only you can make. Houses don't need to be perfectly level, provided they are solid in place and not moving any more.

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