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Thread: Flooring questions

  1. #1
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    Flooring questions

    I have a cabin that was built in 1930 or so. It has log 'joists', abut 4 inch dia, on 24 in centers. The lengthwise span of these joists is about 8 ft each. Each joist is supported at both ends with a much larger log, approx 8 inch diameter. The log structure seems pretty good from what I can tell. The original flooring on this is 3/4" pine T&G planks, approx 4 to 6 inch width. Anyway, someone installed some Pergo over the top of it and didn't fix the problem with the floor which is some softness in a few places due to the 24 in span, possible damage to the floorboards (moisture issues in the past). What I'm planning to do is to remove the Pergo, and install some underlayment. What I'd like is advice on the underlayment. Should I go with 3/4" plywood or is the 23/32 OSB a suitable choice?

    Second question, this is a kitchen area and the base cabinets were installed over the Pergo. Should I remove the base cabinets (this will be a big job I think) or is it OK to remove the Pergo up to the base cabinets and butt the new underlayment right up to the base cabinets?

    Third question, is the underlayment even necessary if I install 3/4 finished flooring over the existing flooring (removing the prego of course, but same question about dealing with the base cabinets?

    I also have to deal with some transisitons to bedroom and bathroom - is it acceptable to have a small stepdown in these areas or should I be working to keep everything on one level?

  2. #2
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    I'd have to see it, but I'd guess that 3/4 flooring would take care of it on top of the original floor, unless there is some spot that there is worry about stepping through now. I'd do something not to have height transitions from one room to the other, even if there is a slight slant to a small width of it. I've done that a number of times. Again, hard to say on the cabinet question. There should be good support under the ends of the flooring there. If when you take the Pergo up, you can move the original floor boards to amount to anything with a foot, I'd take them up and go under.

  3. #3
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    Quote Originally Posted by Tom M King View Post
    I'd have to see it, but I'd guess that 3/4 flooring would take care of it on top of the original floor, unless there is some spot that there is worry about stepping through now. I'd do something not to have height transitions from one room to the other, even if there is a slight slant to a small width of it. I've done that a number of times. Again, hard to say on the cabinet question. There should be good support under the ends of the flooring there. If when you take the Pergo up, you can move the original floor boards to amount to anything with a foot, I'd take them up and go under.
    Tom could you clarify these two points you made:
    "I'd do something not to have height transitions from one room to the other, even if there is a slight slant to a small width of it. I've done that a number of times." DO you mean making the transisiton slope in the doorways?
    "you can move the original floor boards to amount to anything with a foot, I'd take them up and go under." Do you mean that if it feels soft near the base cabinets you would remove the bases and do the floor and then re-install?

  4. #4
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    If it were me, I would:
    1 - leave the pergo under the cabinets. There is no reason to remove.
    2 - level the floor across the entire cabin. This can be achieved by placing thin spacers as needed underneath the plywood. For spacers, I would consider 1/4" plywood (if that was the correct size), linoleum, etc.
    3 - I would install some supports under the floor joists in the soft areas. Typically cement blocks and pressure treated lumber will work fine. If needed, you can put a beam underneath them mid-span and support it with blocks, etc.

  5. #5
    Hi:

    I've had to do something similar..so I rather think the answer is the classic "it depends"

    1) OSB vs plywood depends on annual variation in humidity - the more variation you get, the stronger the argument for good quality plywood because OSB (contrary to many mfg claims) swells/shrinks more. (but don't use chinese made junk plywoods, pay for the usa label)

    2) whether you should remove the pergo under the cabinets depends on how wide their base of support is. The more beams it crosses (and if they look ok friom underneath) the less you should worry about replacing the pergo layer. Also, if the pergo was added later, it may or may not extend completely under them.

    3) 3/4" hardwood flooring will support a huge amount of weight without flexing - but only if your average piece lenght crosses several beams. You can buy (at extra $, of course) wood guaranteed to be of some minimum length like 6 feet. Your choice of wood will be affected by local variations in humidity, but almost any hardwood will give you to the strength needed to justify skipping the plywood layer.

    However.. getting the floor flat across all rooms is tricky, and made much much much easier if you use plywood (even 3/8") as a substrate. Home depot et al
    sell rolls of 1/8" cork that has a vapour barrier on one side: putting it plastic side up on your plywood makes putting the hardwood in much easier too.

  6. #6
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    Quote Originally Posted by Pat Barry View Post
    Tom could you clarify these two points you made:
    "I'd do something not to have height transitions from one room to the other, even if there is a slight slant to a small width of it. I've done that a number of times." DO you mean making the transisiton slope in the doorways? shim it
    "you can move the original floor boards to amount to anything with a foot, I'd take them up and go under." Do you mean that if it feels soft near the base cabinets you would remove the bases and do the floor and then re-install?
    yes, if the floor is soft after taking the pergo up with the cabinets in place, do something to make the floor sturdy again

  7. #7
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    3/4" plywood over 24" OC framing is pretty much the maximum span in the charts I looked at. Do you like a bouncy floor? I'd be looking at 7/8"-1" ply for a substrate, real joy to install but easier to live with. Guess it depends on the budget and how you like the floor to feel? If the cabs aren't sinking I wouldn't worry about them, particularly if they run perpendicular to the framing. I don't count on flooring to add structure, it also adds dead load, and you can't count on joints landing over framing, the stiffening effect is diminished when joints land in the middle of the span, requires some real careful planning and staggering of joints....better off to create a solid subfloor.

  8. #8
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    I'd avoid unsupported sub-flooring edges, which it sounds like what you'll get by not running it beneath the cabs. If you're unable to add support from beneath for those edges then I'd remove the cabs and run the subfloor to the wall. Do it once do it right.

    I'd also avoid tiling over that floor structure due to excessive deflection (or plan to add additional joist support). It sounds like you're planning hardwood planks, though.....should be fine for that.

    I've installed lots of flooring that elevated above adjoining room flooring; transition pieces can be custom milled to a wider width to smooth the transition. I've never had a complaint.
    Scott Vroom

    I started with absolutely nothing. Now, thanks to years of hard work, careful planning, and perseverance, I find I still have most of it left.

  9. #9
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    Quote Originally Posted by scott vroom View Post
    I've installed lots of flooring that elevated above adjoining room flooring; transition pieces can be custom milled to a wider width to smooth the transition. I've never had a complaint.
    Is there a code or rule for how much of a transistion height difference is considered excessive? For example, 3/4 " flooring - I would think, no problem to have a small transistional slope of maybe 6 in width (door jambs). Would 1 1/2" be excessive in that same distance?

  10. #10
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    Quote Originally Posted by Peter Quinn View Post
    3/4" plywood over 24" OC framing is pretty much the maximum span in the charts I looked at. Do you like a bouncy floor? I'd be looking at 7/8"-1" ply for a substrate, real joy to install but easier to live with. Guess it depends on the budget and how you like the floor to feel? If the cabs aren't sinking I wouldn't worry about them, particularly if they run perpendicular to the framing. I don't count on flooring to add structure, it also adds dead load, and you can't count on joints landing over framing, the stiffening effect is diminished when joints land in the middle of the span, requires some real careful planning and staggering of joints....better off to create a solid subfloor.
    I am thinking that 3/4" would be overkill over the top of the existing 3/4" pine subfloor but I am not seeing T&G plywood in other than 3/4" thickness and T&G sounds like the best choice. Would plain old plywood be OK or is T&G the only good way to go?

  11. #11
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    Quote Originally Posted by Pat Barry View Post
    I am thinking that 3/4" would be overkill over the top of the existing 3/4" pine subfloor but I am not seeing T&G plywood in other than 3/4" thickness and T&G sounds like the best choice. Would plain old plywood be OK or is T&G the only good way to go?
    If you already have 3/4" T&G pine subfloor then no need to overlay with additional T&G. You can install your 3/4" wood flooring planks directly onto the pine T&G subfloor, but with 24" joist centers and 3/4 pine subfloor I'd want to add at least 1/2" exterior glue ply perpendicular to the joist direction and screwed to the pine. It won't reduce joist deflection but will stiffen the subfloor between the joists. If installing 1/2" ply raises the overall floor height too high then just install the 3/4" hardwood planks onto the existing pine subfloor perpendicular to the joist direction. It's an improvement from what is in all likelihood a thinner laminate floor.

    In any case, your subfloor joist structure is not suitable for tile or stone...too much deflection.
    Last edited by scott vroom; 09-16-2014 at 4:18 PM. Reason: corrected an error in joist spacing from 4' to 24"
    Scott Vroom

    I started with absolutely nothing. Now, thanks to years of hard work, careful planning, and perseverance, I find I still have most of it left.

  12. #12
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    Quote Originally Posted by Pat Barry View Post
    Is there a code or rule for how much of a transistion height difference is considered excessive? For example, 3/4 " flooring - I would think, no problem to have a small transistional slope of maybe 6 in width (door jambs). Would 1 1/2" be excessive in that same distance?
    You can check with your local code compliance officer, but as a practical matter I wouldn't exceed 5/8" (allows for a 5/8" rabbet from a 3/4" transition piece, leaving an 1/8" overlay on the higher side). You didn't mention the height of the flooring in the adjacent rooms. What is that measurement?
    Scott Vroom

    I started with absolutely nothing. Now, thanks to years of hard work, careful planning, and perseverance, I find I still have most of it left.

  13. #13
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    Quote Originally Posted by scott vroom View Post
    You can check with your local code compliance officer, but as a practical matter I wouldn't exceed 5/8" (allows for a 5/8" rabbet from a 3/4" transition piece, leaving an 1/8" overlay on the higher side). You didn't mention the height of the flooring in the adjacent rooms. What is that measurement?
    Thanks Scott, the adjacent rooms are currently at the same level as the Pergo floor, within about 1/8 inch. room is a bedroom, one other is a bathroom.

  14. #14
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    Here is an update on my floor problem. I started to remove the Pergo and was instantly amazed at the crappy installation. The guy who did this job used thin strips of lath, cardboard, and sometimes Pergo scraps to attempt to level out the floor. He had those strips on about 16 inch centers, perpendicular to the Pergo, with little or no regard tot the seams in the Pergo he was overlaying. Believe me, you need more support than that for Pergo. LOL. Honestly, thats the best news I have. The downside is that the floor, in the area he was trying to fix is not level. It slopes approx 1/4 to 3/8 per 2 ft. Consequntly, the one end (7 ft) has about a 1 1/2 inch difference. Obviously there has been some settling (this low spot is in a corner of the house). More good news is that the sub floor is basically pretty solid. Maybe a few spots where a board or two needs replacement, but basically good. Now I need to decide how to get the floor fixed. I am not certain that I even need to fix the nonlevelness in this stuation. A little non planarity may not be a problem. What do you folks think?

  15. #15
    It's a log cabin so a solid but un-level floor seems perfectly acceptable. As far as removing the cabinetry to get the pergo out that seems like a silly waste of time and could possibly cause more problems. Cheap Cabinetry doesn't like to be installed and then uninstalled and then installed again. Even good cabinetry doesn't like it all that much. I honestly don't know of what benefit it would be to get the pergo out from underneath of it. Are you even sure it goes underneath the cabinets to begin with?

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