Crawl Space

Discussion in 'Remodel Forum & Blog' started by ASG, Mar 30, 2012.

  1. ASG

    ASG New Member

    Messages:
    2
    Location:
    Massachusetts
    So I have a house, it is older, built in 1909 and is a bungalow. Under the living room is a crawl space accesable from the basement open earth floor. I am remodeling, gutting all the way down to the joists and studs. What is a less expensive way to offer some insulating factor for the floor above without choking out the air flow needed to prevent rotting? Can I run some fiberglass insulation inbetween the joists? If so, what would the reccomended type be, faced or unfaced or foam sheets? And is there a best R rating I can use in this case, or am I completely on the wrong track here?
  2. Dana

    Dana In the trades

    Messages:
    2,986
    Location:
    01609
    Better solution is to air-seal an insulate the crawl space converting it to a conditioned crawlspace, closing off ALL venting, which puts all of the wood inside of conditioned space where it's warm & dry, and rot-free. More details here.

    Any approach that insulates between the joists leave the joist edges colder, more likely to be below the dew point of the crawl-space air.

    At a minimum you'd want to put a 10-mil poly vapor retarder on the floor, but if it's nice and level and you can get full sheets in there 2-3" of rigid EPS roofing insulation would work for both the dirt floor and foundation wall insulation. (Reclaimed goods are dirt-cheap at The Insulation Depot in Framingham MA, if you can pick up- they don't deliver small quantities. From them and similar sources it's usually cheaper per unit-R than virgin-stock fiberglass batts!) If it's a fieldstone foundation it may be easier to insulate the both crawlspace walls and the band joist, with ~2" of closed cell foam (about $2 per square foot of coverage, end result is ~R13),and EPS on the floor, with the vapor barrier between the dirt & floor.

    If you still want to leave the walls uninsulated, at least crudely cut'n'cobble in at least 3" of EPS or fiber-faced iso (sometimes available in Framingham, or search craigslist/materials for other sources) onto the band joist & foundation sill, air-sealing it and filling in the edges/seams with 1-part spray foam. You can then put in ~2.5-3" of rigid foam (any type) up on the bottom of the joists to insulate the floor, holding it in place with furring every 24", though-screwed to the joists with screws that penetrate the joist by at least 3/4". The seams & edges would need to be air-sealed with 1 part foam or duct mastic, etc. That way you'd have a comparable or greater R value than the exterior walls, all the susceptible wood stays at the indoor temp & humidity, and it would be air-tight for minimal infiltration.

    If you use iso on the walls, be sure to lap the floor vapor retarder between the foam & foundation for the first 12" off the floor, or it may slowly pick up moisture.

    If in spite of this advice you insist on going with a batt solution, go with unfaced batts thick enough to fill up the cavity completely, and use Tyvek or similar for a bottom-side air-barrier. If you went with kraft faced batts with facers on the bottom for ease of installation it would all but guarantee a mold problem within 10 years in most MA locations.

    FWIW: My central MA bungalow is only14 years newer than yours, and has a section of crawlspace under the master bedroom- I've starred in this movie. :) Someone had previously installed kraft faced batts, facer-side down, and yes, it was more than just musty in there! I've since done a DIY- R20 in rigid foam on the walls, and removed the moldy batts, as well as putting a vapor retarder on the floor. Access is only via a 15" x 18" port , so getting in full sheets to lay down on the crawlspace floor or underside of the floor joist isn't possible without some dirty demolition/rebuild, so for the time being it's vapor-barrier only on the floor. The average floor temp over the crawlspace section is still a couple degrees less than the part over the more-conditioned basement, but it doesn't stink of mold (anymore) and it's never frigid.
  3. ASG

    ASG New Member

    Messages:
    2
    Location:
    Massachusetts
    Thanks

    Thanks Dana, that was exactly what I was looking for. I am doing a full remodle, so I think it will be easier to do all this after I pull the subfloor up. Up towards the front it reduces all the way to about 2-3 ft from ground to joist and I am not a small guy and the wife refuses to do it!
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