i need a 4 inch subfloor

Discussion in 'Remodel Forum & Blog' started by mtbmike, Dec 30, 2010.

  1. mtbmike

    mtbmike New Member

    Messages:
    8
    Location:
    shrewsbury, ma
    hi, i have a six year old house in Mass with a 2 car garage under. The garage takes up a little more than
    half the basement area. There is a boiler room and a future bathroom in the other half. Both the boiler
    room and the bathroom are poured 4 inches higher than the garage floor, code here to contain spilled
    gasoline, i guess. I now want to build a rec room across the back of the garage, which will abut the bathroom. I need to raise the floor to match the other room - 4 inches. I wanted to do a subfloor using 6ml poly, sleepers, and 3/4 osb.

    laying pressure treated 2x4s topped by 3/4 osb only gives me a 2 1/4 inch rise (will be carpeted but i
    would think pad + carpet = 1/2 inch?)

    if i lay out the 2x4s on edge and top with osb, i'll be 4 1/4, which should work because i still have to
    finish the bathroom floor, i plan tile, so probably 1/4 cement board and 1/4 tile would be a total of
    4.5 inches above the existing garage floor.

    not sure how to anchor the sleepers in this position, tho. Drill and tapcon? i was hoping to use
    my ramset but i don't think they make a concrete nail long enough to do that.

    i would appreciate any advise! either another way to gain the 4 inches, or the best way to anchor
    the sleepers.
  2. cacher_chick

    cacher_chick Test, Don't Guess!

    Messages:
    3,249
    Location:
    Land of Cheese
    Maybe consider a complete frame, as if you were building a deck, but with 2x4's.
  3. Dana

    Dana In the trades

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    Location:
    01609
    The thermal losses through the slab are substantial- I'd only go as low as 3/4" XPS if there were no headroom- here you have the opposite problem- fill that up with insulation! If you're looking for a 4" lift skip the sleepers, use 3.5"-4" EPS with t & g OSB or ply long-screwed to the slab. That way you'll get R14+ of insulation underneath the whole shebang, with no timbers to thermally short-circuit it so it won't feel so much like a basement under foot (it might end up being one of the warmest floors in the house.)Hammerdrill & 5" masonry screws 24" or less on center should do it. The structural compressive loading of even lowest-density Type-I EPS is more than enough for a residential flooring app with a 3/4" t&g subfloor- just don't park your bulldozer on the edge.

    You can get recycled used-once roofing EPS from The Insulation Depot down the street from you in Framingham for VERY cheap if you pick it up- they won't deliver in less than tractor-trailer load quantities. Most of it's been stripped from big flat roofs.) If they don't have EPS that stacks to the right thickness XPS will do, but not iso.

    EPS and XPS are soluble in gasoline, but if you spill enough in there to melt the stuff you'll have a bigger problem than a low spot in the edge of the floor, eh? ;-)
  4. mtbmike

    mtbmike New Member

    Messages:
    8
    Location:
    shrewsbury, ma
    thanks both for your ideas, Dana, I can't believe you even gave me a location nearby to check out! i'll be calling them
    tomorrow and will follow your suggestion... i'll feed back once done. Thanks Again!
  5. Dana

    Dana In the trades

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    Location:
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    Be sure to lap the seams of any layers of EPS by a foot or so, as well as lapping the seams of the subfloor with those of the foam to get maximal floor loading capacity across seam boundaries. If the seams are all lined up with each other it's possible to end up with a slight rockering at joints if you spend time jumping rope at the seam edge. Lapping the seams and using t&g subflooring takes those issues off the table.

    Any broken corners or gross imperfections in the foam can be filled with 1-part foam and trimmed flush before laying down the subfloor. Expect to be trailing li'l white EPS beads around for awhile after cutting the foam to fit- vacuuming them up after every cutting session helps keep them out of the house though. They're clingly li'l staticky suckers- vaccuum them off your clothes too. XPS sawdust will trail you around too, but not quite as aggressively as EPS beads.
  6. Gary Swart

    Gary Swart In the Trades

    Messages:
    7,359
    Location:
    Yakima WA
    Ripping 1/4" from the edge of 2x4s is a pretty simple task for a table saw.
  7. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,831
    Location:
    Cave Creek, Arizona
    Glue them down with construction adhesive. But every garage I have seen has a "sloped floor" for drainage, and if yours is like that then you will have to consider ripping the stringers to level the floor. Garage floors typically have a 1/4" per foot slope, which WOULD be signicant in any room more than 2' wide.
    Last edited: Jan 7, 2011
  8. Dana

    Dana In the trades

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    Use only "foam board construction adhesive" (it's available at orange or blue box stores) on anything in contact with EPS- the solvents in standard construction adhesive melts polystyrene. If floating the floor on an EPS pad (no intervening sleepers, joists, etc) you may have to level up the floor with something else first if there's enough slope to matter.
  9. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
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    Location:
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    quote; Use only "foam board construction adhesive" (it's available at orange or blue box stores) on anything in contact with EPS- the solvents in standard construction adhesive melts polystyrene.

    I would hope they are NOT building the floor an a bed of "foam board" but rather using 2x4 stringers, with or without foam between them which would NOT have to be secured, (and why anyone would use it in a situation like this confuses me).
  10. dlarrivee

    dlarrivee New Member

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    1,172
    Location:
    Canada
    Time to come out of the stone age HJ.

    Using 2x4s will only create tons of thermal bridging to the slab below.

    If you have a problem with an idea like this you obviously haven't been around much modern commercial construction.

    Ideas from 60 years ago are only going to create a cold floor, with NO benefits. The compressive strength of XPS is plenty for putting plywood ontop of and adding living space above a slab.
  11. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,831
    Location:
    Cave Creek, Arizona
    But it will ALSO create a floor which is parallel to the existing concrete floor which is PROBABLY NOT level. If that is the case, what is your solution? Get a machine of some kind and "grind" the floor level or shave the bottoms of each plank as you install them to create a level floor.
  12. dlarrivee

    dlarrivee New Member

    Messages:
    1,172
    Location:
    Canada
    I'm not there, so I don't know how uneven or untrue the floor is.

    There are lots of options here, depending on the severity.

    Worst case scenario, I'd use a hot wire foam cutter to adjust the thickness as required.

    Best case, a few composite shims and some thin veneer ply might be all that is needed on top of the foam.

    Hard to say how much extra work this might be, but I would avoid at all costs allowing wood to touch subfloor and slab in a continuous plane.
  13. mtbmike

    mtbmike New Member

    Messages:
    8
    Location:
    shrewsbury, ma
    insulation depot was a great pointer. was a little difficult to get a return call, but once i did,
    i got 3 inch eps for $4 for 2x8 sheets in perfect condition. couple of questions -

    there's mention in this thread of gluing the eps to the floor, but i believe i need to use
    6 ml poly under the eps to protect against any moisture. isn't that correct, and doesn't that
    mean i cannot glue?

    also, since its only 2 foot wide, i'll have alot of seams. should i tape these before i lay the osb over it?
  14. Dana

    Dana In the trades

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    Location:
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    Taping the seams with housewrap tape isn't absolutely necesssary. A thin bead of adhesive along the edges to marry the boards together as you install it might be easier.

    At 3" thickness EPS with taped/sealed seams has a vapor permeance between 1.5 perms, which would be more than sufficient to protect a wood subfloor with hardwood, ceramic tile, or carpet finish flooring. If the slab normally stays dry and you aren't using a vapor-impermeable flooring like vinyl, ground moisure will dry toward the room through the flooring rather than accumulated in the subfloor. EPS won't wick water- it's a closed cell structure- any moisture absorption stays in the interstitial gaps between the beads, and won't affect it's structural rigidity, and barely affects it's R-value.

    If you want to play it absolutely safe or if you're using a low-perm plastic or asphalt-tile finish floor, put the poly on TOP of the EPS, between the EPS and wood (which would also give the wood a slip-surface.)
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