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Thread: Workshop subfloor over crawlspace?

  1. #1

    Workshop subfloor over crawlspace?

    How much subfloor do I need over a crawlspace for some really heavy machines? The joists are sized correctly but I worry I need thicker floor. The builder put down 3/4" Advantech OSB which seems pretty stout, but a 1500 lb machine on it might make me reconsider.

    Right now I'm leaning towards putting down SPC vinyl due to the impact and scratch resistance, though there's a small chance I could wind up with solid oak.

    If I go vinyl, should I lay down another layer of OSB or anything to stiffen things up?

  2. #2
    Join Date
    Mar 2018
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    Orwell, NY
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    What is the joist spacing? That will go a long way to determine whether a heavy machine will be okay. Also, are the machines going to be in fixed locations where they are sitting on joists, or on casters roaming around?

  3. #3
    Join Date
    Feb 2010
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    Mt Pleasant SC
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    Hopefully you have access underneath to add several posts sitting on proper solid blocks or poured concrete. What is the length of the joists? Probably need a post under each joist that is under the machine feet. If the machine feet are resting in between joists you need blocking underneath too. Long term loads like this will cause sagging in the floor system that can only be repaired by removing the subfloor and sistering the sagging joists then new subfloor.

  4. #4
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    Just off the top of my head if supported only by joist that are are 16" or 24" o.c., I would have preferred the 1.25" advantech. If you decide to add another layer, I would go with an osb product, resin makes it harder and no voids. It is too bad the advantech is already down. Very stiff, water and humidity resistant and guaranteed no sand edges for a year, even if stored in a puddle. I would be prone to leave that as my finished floor... (actually, I did. .. 3/4" , but continuous support from 25psi Foamular). But, then, you could go with another 1/2" or 3/4" advantech instead of your vinyl planks (I would be more concerned with vinyl under a 1500 pound machine).
    Comments made here are my own and, according to my children, do not reflect the opinions of any other person... anywhere, anytime.

  5. #5
    Join Date
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    SE PA - Central Bucks County
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    Hopefully, the joist spacing is no more than 16" OC. I'd add a second layer of the Advantech with joints staggered from existing with glue and fasteners. As someone noted, the 1.25" Advantech (or the LP equivalent0 would have already solved the issue, most likely, had it been installed in lieu of the .75" version. That's strong, stout stuff!
    --

    The most expensive tool is the one you buy "cheaply" and often...

  6. #6
    I don't recall joist spacing, but there is a giant extra pillar right in the middle where the heavy stuff goes. I explained my use to the contractor and he made sure to do his magic on it, so the beams/spacing/pillars are solid.

    Sounds like another layer of Advantech would be wise. I'm also looking at the SPC flooring, which is a stone composite that should be more dent/impact resistant than wood. I got a sample of it and wailed on it with a hammer and it hardly seemed to notice.

  7. #7
    Join Date
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    I wasn't doubting the overall strength of the floor to hold the load, but the longer the space between the joists is the thicker the subfloor will have to be to resist sagging with a heavy point load. I suppose another thing to think about it how much surface area the 1500 lbs is spread over. A drill press or bandsaw, for instance, will have a lot of floor contact, and some old jointers I've seen in pictures have hardly any.

  8. #8
    Join Date
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    SPC is really stout stuff; we are putting it in our kitchen. Verify with the particular brand you are considering, but Coretec, for example, requires glue down installation (not floating) when there will be heavy loads. And glue down is recommended when there will be rolling loads.
    --Certainty is the refuge of a small mind--

  9. #9
    Quote Originally Posted by Zachary Hoyt View Post
    I wasn't doubting the overall strength of the floor to hold the load, but the longer the space between the joists is the thicker the subfloor will have to be to resist sagging with a heavy point load. I suppose another thing to think about it how much surface area the 1500 lbs is spread over. A drill press or bandsaw, for instance, will have a lot of floor contact, and some old jointers I've seen in pictures have hardly any.

    Ah yes I see what you're saying. I believe the joists are 16" if I remember right.

  10. #10
    Join Date
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    Quote Originally Posted by Bert McMahan View Post
    Ah yes I see what you're saying. I believe the joists are 16" if I remember right.
    That's easy to check... And you don't have to go into the crawlspace spelunking if you don't want to. Just measure the distance between the rows of fasteners on the top of the existing subfloor.
    --

    The most expensive tool is the one you buy "cheaply" and often...

  11. #11
    Join Date
    Jan 2008
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    Western Nebraska
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    You'd really need to know span, joist spacing, joist size/type/series if TJI, machine weight and distribution, and total floor load to be able to accurately calculate the deflection. Have you noticed a problem prior to the machine sitting there? If so, you can probably guess pretty accurately if you need more subfloor or joist support. Loaded refrigerators and freezers generally have similar weights to heavy shop machines, so a floor adequate to hold them will generally be good enough for a shop. Keep in mind that more subfloor changes floor transitions and thresholds.

  12. #12
    Join Date
    Nov 2013
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    Waterford, PA
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    914
    My shop floor was engineered. It has 2 beams sitting on posts so that each joist span is just under 8'. Those beams carry 2x10 joists spaced 12" on center. There is then 3/4" plywood over the joists, 3/4" OSB sleepers to accomodate the radiant floor tubing and then 3/4" plywood that is my shop floor. With that arrangement, I more or less have a 2-1/4" floor. I've never had any problems with machines causing the floor to sag or anything. Even the new slider didn't cause any detectable deflection.

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