Basement subfloor, how exactly should I do it?

Discussion in 'Remodel Forum & Blog' started by protivakid, Oct 14, 2013.

  1. protivakid

    protivakid New Member

    Messages:
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    Location:
    MA
    I am finishing a basement with my father and want to put in a subfloor. I know if there was ever enough water I would probably have to replace the floor anyways but want to give myself a couple inches more so to protect the expensive electronics I will have down there. There is also a sewer access port and two ground rods that stick ~ 2 inches above the concrete floor.

    We were originally planning to lay down pressure treated 2x4's the tall way getting us over the two obstructions and build a plywood floor on top of it. After that we were going to build two small access panels in the floor should we ever need to get to them.

    An uncle who is a carpenter stopped by this weekend and said if it was his basement he would not even bother building a subfloor. He said the basement was bone dry and it would be a waste. Even if we did get water it would be trapped in between the 2x4's with no way to get it out. The obstructions are in a corner so we would just box them in somehow going that direction.

    This now puts me back to planning. I can't see a disadvantage to building a subfloor other than money and height though the ceiling down there is 8ft so height is not an issue.

    What is the best way to build the basement subfloor? I have seen other methods such as Dri-Core or Delta-FL also suggested. Ideally I would like to create channels so I could somewhat push water out should I ever have an issue. From concrete to carpet please advise me exactly what I need to do in-between.
  2. Reach4

    Reach4 Active Member

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    While waiting for somebody with experience, try searching for dricore barricade Delta-FL
  3. protivakid

    protivakid New Member

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    23
    Location:
    MA
    I did a couple hours of goolgeing last night and I am now left with more options than I know what to do with. I would lean toward a standard 2x4 & plywood method but would really like some sort of channels under the floor.
  4. Dana

    Dana In the trades

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    I'm not quite sure what you exactly hope to gain with the 2x sleepers- drainage channels?

    MA there's a long term energy use rationale for putting R8 or so of insulation between a finished conditioned basement and the ~50F subsoil, and a short-term mold-hazard reason to put down at least R4. To get there without creating a mold-farm, skip the sleepers, lay an EPDM or poly ground vapor barrier on top of the concrete, then 2" of EPS foam (R8), then put half-inch t & g OSB or plywood sheathing on top of that, Tapconned to the slab at most 24" o.c. (to limit curl & waves), over which you can install any standard flooring that its at least semi-permeable to water vapor.

    You could also use XPS (pink/blue/green board), but the blowing agents used in manufactor have extremely high global warming potential (more than 100x those used for blowing EPS, and more than 1000x C02), and it all leaks out over a handful of decades, resulting in R-values that are identical to EPS at the same density by year 100. You CAN'T use polyisocyanurate (the pale yellow stuff with the foil facers), since it it modestly hygroscopic and can eventually take on water, losing most of it's perfromance. (You can safely use polyiso on the interior side of foundation walls though, as long as you keep the cut-edge off the slab, but not on floors.)

    If you finish the floor WITHOUT the insulation (just the vapor barrier) the wood stays cold enough to take on moisture even from the summertime ventilation air, and the bottoms of cardboard boxes would retain sufficient moisture that they would be at high risk of mold.

    If your foundation walls are not insulated, it's WELL worth insulating them to at least 2' below grade in a MA climate. But you can't just throw up a studwall & fiberglass batts without creating a mold farm. If this is a project you'd be interested in, I could explain a few ways how to go about it (with a few different price/performance points.)
  5. protivakid

    protivakid New Member

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    Location:
    MA
    I need to raise the floor a few inches to get over the two obstructions I mentioned before, ground rods & sewer access. I also thought that if the basement did flood, the raised floor would at least give me a couple inches to catch the leak and get my electronics out of there. My desire for channels underneath that floors like the Dri-Core provide was so that any water could run and I could try to such / blow it out of there in the event of a leak. Is this logic flawed?

    I will take any suggestions and preferably links to products for the floor & walls. Layer by layer let me know what is the best way. Reading above it sounds like you gave some great suggestions. Will the foam allow water to travel if it did get under there? Will it feel solid under my feet if I put plywood & carpet on top of it?
  6. Dana

    Dana In the trades

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    Dri-Core etc provide some degree capillary break, but aren't exactly drainage systems.

    EPS foam is waterproof (it's used for dock floats, and lobster-pot buoys, after all). XPS is too. In MA there are several sources of rigid foam reclaimed from building demolition &/or factory seconds, either of which would be fine in your application, as long as it's EPS or XPS. The Insulation Depot will sell to small-lot customers who show up with their own truck, but will ship only in tractor trailer loads, and will usually have just about any thickess of EPS on hand (Their warehouse is at 703 Waverly Street in Framingham, Phone: (877) 311-0175. Email: Info@InsulationDepot.com )

    If you have sufficient water under the subfloor that the water actually needs to move, you're pretty much screwed even with the dimple-mat systems or Dri-Core,e

    Foam fully supported by concrete with half inch to three quarters ply/osb over it (seams of the subfloor staggered with those of the foam) is more rigid than, and flexes less than standard subfloors spanning 16" o.c. joists with 3/4" hardwood flooring.

    The cheapest way to get a truly high-performance basement wall insulation is to put a minimum of 1" of foam (any type) against the foundation, and trap it there with a 2x4 studawall with R11-R15 UNFACED batts. A minimal 1" EPS using R11 batts results in a "whole wall" R of about R13 after the thermal bridging of the studs is factored in, which is comparable to 2x6 construction with R19 batts and wooden siding. But using 2" of reclamed fiber-faced roofing iso for the foam and R15 rock wool for the cavity fill brings it up to R22-R23. With an interior side studwall approach it's best to run the wall foam down to meet your floor foam, and install the subfloor & bottom plate snug up to the wall-foam. The compressabilty of the floor foam isn't much of an issue, since the studwall isn't structural- it only needs to hold up the gypsum, not the house. For the same reason, it's fine to use 24" o.c. stud spacing and single top-plates to the stud framing.

    Alternatively, 3" of reclaimed roofing iso held in place with furring TapConned to the foundation with 24" o.c. fastener spacing is about R18-R19 (depending a bit on the density of the iso), and you can hang the wallboard on the furring. It takes 4.5" TapCons though, which you may have to find on line- not all box stores carry them that long. (This is how I insulated my basement in Worcester.) Typical pricing on 4'x8' sheets of reclaimed iso in nearly-perfect shape is $12-20/sheet, which on a per square foot basis costs less than crummy low density R19 batts. The TapCons add a bit to it, but it's still pretty cheap & easy- less labor than studwall approaches too.

    With either approach, you need to foam or mastic seal the seams of the foam, and foam-insulate & seal the band-joist and foundation sill to the wall foam. The cut'n'cobbled foam can be cut pretty loose for fit, fixed in place with foam-board construction adhesive that uses solvents compatible with foam (available at box stores), and use expanding can-foam (or Froth Pak) to seal up the edge & seam gaps. You can then use carefully trimmed/fitted high density batts (rock wool preferred, but "cathedral ceiling" fiberglass is OK) on the interior side of that to fatten up the R-value, and to provide a thermal barrier against ignition (per code it needs at least 3", or else you'd need to box it in with wallboard.) With 2" of roofing iso and R15 rock wool you'd be in pretty good shape at the band joists.

    If you're not planning to finish the basement out, 2" of closed cell spray foam painted with intumescent paint to meet fire code makes it, ~R13 whole-wall at about $2.50 per square foot.

    You may find this bit o' bloggery useful.
    Last edited: Oct 14, 2013
  7. protivakid

    protivakid New Member

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    Location:
    MA
    Any who, with that place in Framingham, what was your reason to recommend buying from them over another place? Best price? Environmentally friendly? Only place that sells the stuff? I also noticed you said the stuff is second hand, is there anything I need to look for when picking through the sheets or are they all ok? What length/width dimensions do the sheets come in?

    If I go with foam, will going thicker, say 3 inches, be too much that the floor will feel like a sponge? I need it high enough to get over my ground rods. Do I bring the foam and plywood right to the edge of the stud wall or leave a 1/4 inch gap for any type of expansion?

    Will the foam move small amounts of water just as well as the dri-core will? What is best to use between the foam and concrete, Saw some suggest painting the floor with a sealer.?

    For the walls, my house is a split level so the concrete only comes up 5 feet from the floor in the back and steps down to about a foot in the front. From there its 2x4's and pink insulation on top of the concrete to the ceiling. Should I only put foam up to where the concrete ends or go all the way up to the ceiling. I can provide a pic of my basement if needed. It sounds like you recommend foam similar to what we are using on the floor, then 2x4', with unfaced batts in-between?
    Last edited: Jun 17, 2014
  8. Dana

    Dana In the trades

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    Price & availabilty, drive time, etc. all add up. There's an outfit in Auburn selling factory seconds on foil-face iso for cheap on craigslist, but several vendors selling reclaimed goods. They don't always have the same stuff in stock. Only Insulation Depot advertises their contact info widely(which is why I posted that info)- the others seem to prefer advertising only on craigslist using email for the initial contact rather than paying somebody full time to answer the phone. If you can email them the specs & quantity of what you're looking for (eg "I need about 1500 square feet of 3-inch EPS, and 1200feet of 2-inch." ), they usually respond right away if they have it, and the price is typically 20-30% of virgin-stock distributor pricing. Some will deliver for a nominal fee if you're close enough.

    The floor will NEVER feel like sponge, even with 10" of EPS under it, if fully supported by the concrete. (And 3" is one of the most common thicknesses of roofing EPS.)

    Stop thinking of Dri-Core as a drainage matrix for water to flow thorugh- it really doesn't function that way. It DOES function as a capillary break for moisture wicking up from the slab, but so does 10mil poly + 2-3" of EPS.

    It's fine to go all the way to the ceiling with the foam on the pony-wall. If you trap it with a batt-insulated studwall rather than furring through-screwed to the foundation, only use unfaced batts.
  9. protivakid

    protivakid New Member

    Messages:
    23
    Location:
    MA
    Thanks for the info. So I go concrete, EPDM, Foam, Plywood, Carpet right to the edge of the studwall.

    For the EPDM, will that liquid rubber stuff work or should I be looking for a roll?

    For the wall put up foam to the top covering the concrete & existing studs/pink insulation and then put up the interior studwall between?
  10. protivakid

    protivakid New Member

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    Location:
    MA
    In addition to my above questions, do they make Tapcon long enough to go through the 3 inches of foam and plywood?

    How thick of a poly vapor barrier am I looking for?
    Last edited: Oct 16, 2013
  11. Dana

    Dana In the trades

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    EPDM is a roll type membrane, not a pourable liquid. Ideally it would extend wall-to-wall and up to about grade level on the walls. For ease of installation it's usually brought all the way up to the foundation sill. If you want to use poly, 10-mil is recommended.

    Sure-take the wall foam all the way up, and install the finish studwall tight to the foam, with no hidden gaps or voids. Voids/cavities would become thermal bypass channels for convection around the insulating layers, undercutting the thermal performance of the walls.

    The longest 1/4" shaft TapCons is 6", but they also make 5-inchers, which is long enough for anchoring to the slab even with ~3/4" subfloor.
  12. protivakid

    protivakid New Member

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    Location:
    MA
    Called the hardware store and they recommended I not use OSB for a floor and use plywood instead but game me a quote on both anyhow.

    Called Insulation Depot and they only have 2" ISO in stock at the moment. Emailed some of the craigslist guys and hope to hear back soon.

    Looking for 10 mil poly barrier has also been tough. One guy was surprised I would need it to be that thick and most places including Home Depot only stock up to 6 mil in store. Waiting on a call back from a local place to see if they have a roll of 10 mil in their yard.

    Anyone know another place to buy tapcons? Lowes and Home Depot don't seem to stock the 5 inchers in store.
    Last edited: Oct 17, 2013
  13. protivakid

    protivakid New Member

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    23
    Location:
    MA
    Got this project started today but man are those tapcons a pain. We drilled the hole but the tapcon only goes in a bit before struggling. Even hand tightening them I broke one and the 3 others we tried felt like they were going to snap so I backed off. We are using the right size bit 3/16ths for the 1/4 tapcon but only got one or 2 in correctly. I ordered a better Boche drill bit that says it will last longer going into concrete so hoping that will drill a better hole and fixes our issues.
  14. protivakid

    protivakid New Member

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    Location:
    MA
    As an update I think we have gotten the hang of this. The tapcon and other drill bits we tried from the local store are junk. They claim masonary but concrete is just too much for them. After drilling a half dozen of holes they were worn right down. I ordered some Bosch Extreme bits from Amazon after reading reviews and have drilled 40+ holes with one and its still good for more.

    Also figured out how to better get the tapcon in and the answer is cleaning out the hole. Concrete dust does not compress like wood dust so my guess is, though we drilled an inch+ into the concrete, the bit was hitting the dust and refusing to go further. Using a can of compressed air with its red long needle like tip to get down into the hole, along with a shop vac & micro attachment nozzles does a great job of getting all the dust out of there. From there we carefully use a drill to get the tapcon in a bit and hand tighten the last few turns.

    This method worked great and we did not snap a single tapcon yesterday. Still have to finish getting the rest in, only 75 more to go haha.
  15. johnfrwhipple

    johnfrwhipple I love these ACO Shower Drains - Best in Class

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    4,122
    Location:
    North Vancouver, BC
    Here in North Vancouver I'm currently working on my own basement floor.

    I have always wondered about a good thermal break for these old Vancouver homes and I am trying a few things "Outside the Box".

    For one - I'm not using any fasteners into the concrete.

    For two - I'm using 1/2" foam everywhere directly bonded to the concrete.

    The subfloor has been down now for about 4 months and looks great. No movement - nothing.

    Over the 1/2" foam I installed plywood 5/8" - again just with thin-set and braces.


    It will be curious how this install holds up over time or even if it does.

    I have been waiting to post the pictures until after I get more work done.

    To prevent a disaster I'm also installing a gravity feed drain line from the powder room entry to the garage. This looks really slick.
  16. Dana

    Dana In the trades

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    Using foam-board construction adhesive works well long-term between the sub-floor and foam, but the bond to the concrete may eventually give up in time, depending on the moisture content of the concrete, and the shrinkage rate of the foam. (XPS will likely have a bigger issue than EPS here.) Many solvents will degrade foam, so sticking with the purpose-made adhesives is advisable. Moisture changes in the plywood can also cause upward forces, pulling away from the concrete forming "waves" in the floor. But if the slab has a poly vapor barrier the risk of breaking that foam/concrete bond is lower, since the moisture content of the concrete will be less, and the humidity stresses causing the wood to curl are lower.

    A half-inch of foam isn't much of a thermal break against the +10C subsoil of Vancouver.
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