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  1. #1
    Join Date
    Oct 2013
    Posts
    5

    Default New Subflooring on Existing Pine Plank Flooring

    Hi All,

    My wife and I just purchased a Philadelphia row house (circa 1886) - A bit of a fixer upper, but sturdy nonetheless. The structure is good, except the pine hardwood floor planks. Clearly they have seen better days. There is noticeable water damage from underneath, huge gaps filled old wood puddy, knots that are beginning to pop out, nails starting to pop back up, etc. Unfortunately, there is no sense in sanding the floors, since many of the planks need to be replaced.

    We have a contractor putting up an addition on the back of the house, and he said if we were considering installing new hardwood floors the best way to go would be to install a new subfloor perpendicular over the existing pine planks, followed by the new hardwood floors. He said 1/4" luan would do the trick (followed by some leveling/shimming in low-lying areas). We were originally were going to do this for just the first floor, but since we have some extra money, were planning to do the same for the entire second floor as well.

    So here come the questions:

    - Is 1/4" luan plywood study enough to use on both levels? Is 1/2" better? OSB or Plywood?
    - How would you install the subfloor? Staggered? 1/8" spacing? T/G? Liquid nails followed by screws along the joist lines?
    - My biggest question is since I would be increasing the floors 1/4"-1/2" on both levels, how would approach the stairs? There is one set of stairs along the party wall, and adding these new floors would throw off the treads and risers on both sides. Any recommendations on how to approach that issue? The stairs, poles, railings are original to the home, so I would hate to mess up the original design, or compromise it's structural integrity.

    Any help in answering this list of questions would be greatly appreciated. Thank you!

  2. #2
    Join Date
    May 2012
    Posts
    133

    Default Re: New Subflooring on Existing Pine Plank Flooring

    My opinion as a DIY owner...rip up the floors, inspect and level the joists (may have termite or water damage), and then put down your new floors while insulating between the joists.

    If you're going to do something, do it right for the long term rather than what is expedient or less costly.

  3. #3
    Join Date
    Dec 2010
    Location
    Houston Texas
    Posts
    2,358

    Default Re: New Subflooring on Existing Pine Plank Flooring

    1- 1/4" Lauan in NOT a structural panel and add NO stiffness to the floor (deflection reduction) Its simply a soft bodied filler used more commonly for underlayment for vinyl flooring. It will do nothing but make your hardwoods 1/4" higher.

    2- Patch the planks and install the hardwoods either perpendicular to the joists or parallel, provided the planks are at a 45 to the joists. Adding more subflooring should be no less than 1/2" CC or better plywood, with the face grain perpendicular to the joists. Use no glue, but instead fasten the plywood with screws. The glue will create voids below the plywood, unless you can get 100% full spread with the glue. Screw the plywood to the planks after the planks are screwed to the joists.

    3- Most codes allow as much as a 3/8" variation between risers. Check with your local authority.

  4. #4
    Join Date
    Oct 2013
    Posts
    5

    Default Re: New Subflooring on Existing Pine Plank Flooring

    Thank you both. Two very different responses ...

    I am leaning toward the 1/2" plywood on top of the existing pine planks, only because it adds more stiffness to the existing floor. I like the idea of reinforcing the existing floor with new plywood.

    However, I am still not sure how to match the stairs ... Are there kits that I can use? Do I need to build a whole new set of stairs? If I add 1/2" of plywood and 3/8" of engineered wood floors that is a total of 7/8" thickness I am adding to the existing pine planks, which means the first riser going down to the first level will be 7/8" higher than it was before, and not the same size as the other risers. What do I do in this situation?

  5. #5
    Join Date
    Dec 2010
    Location
    Houston Texas
    Posts
    2,358

    Default Re: New Subflooring on Existing Pine Plank Flooring

    By code you will be building a new set of stairs.

    Your other option is to remove the plank flooring and replace it with new plywood.
    Last edited by HoustonRemodeler; 10-07-2013 at 10:29 PM.

  6. #6
    Join Date
    Oct 2013
    Posts
    5

    Default Re: New Subflooring on Existing Pine Plank Flooring

    Thanks for the quick response. If I were to remove the existing plank floors, how would I go about leveling the new plywood, since there are some saggy areas? Would you recommend cutting 1/4" to 1/2" filler strips the wide of the joist and screwing/gluing on top? Or just drill in shims? I am just trying to understand the magnitude of the project. Thanks again!

  7. #7
    Join Date
    Dec 2010
    Location
    Houston Texas
    Posts
    2,358

    Default Re: New Subflooring on Existing Pine Plank Flooring

    To reduce deflection of the joists - its best to sister the joists at least 2/3 the span or full span if at all possible. You can 'crown' the new joists when setting them, then plane the tops to pool table flat. Use deck screws and PL Premium glue to glue the sisters to the existing joists.

    If need be you can add additional joists at the same time, depending on the joist spacing already.

  8. #8
    Join Date
    Oct 2013
    Posts
    5

    Default Re: New Subflooring on Existing Pine Plank Flooring

    How would you attach the 3/4" plywood to the existing joists? Would you glue and screw? Or just screw, because they are older?

  9. #9
    Join Date
    Dec 2010
    Location
    Houston Texas
    Posts
    2,358

    Default Re: New Subflooring on Existing Pine Plank Flooring

    Glue and screw as though everything were new. You can also use ring shanked flooring nails.

  10. #10
    Join Date
    Jul 2010
    Location
    SoCal
    Posts
    5,073

    Default Re: New Subflooring on Existing Pine Plank Flooring

    Glue and screw is better. Don't use any ol' screws, use flooring screws.

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