insulation

Discussion in 'HVAC Heating & Cooling' started by ussfox, Dec 1, 2009.

  1. ussfox

    ussfox New Member

    Messages:
    3
    Location:
    pennsylvania
    Gentlemen, I'm looking for some recommendations on types of insulation to use to insulate my basement ceiling after I have installed a pex radiant heat system under my kitchen. I have a lot of obstacles in the way such as joist supports, wiring, copper lines, etc.. I notice some of the bubble wrap type has different r values, I have see some as high as r-30. It looks like I'm gonna have a lot of cuts to make. Has anyone had any experience with a cluttered ceiling? TIA
    :)
  2. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,180
    Location:
    New England
    Some of the bubblewrap stuff is rated differently than say fiberglass or foam...if it has an aluminized layer, they treat it as a reflective layer in addition to the insulating/conduction layer. Heat moves in both radiation (black body) and reflective manner. Fiberglass and say foam slow heat migration by minimizing radiation losses. Foil barriers don't slow it, but redirect most of it. A radiant barrier needs an air gap on each side in order to work or it becomes a good conductor.
    So, if the cold side of the floor is unheated, you need to slow radiation into that cold space, you need something like fiberglass or foam (it would be tough to pack cellulose into that space). Spray foam might mean any maintenace repairs on pipes and wiring would be nearly impossible, so foam sheets or fiberglass are probably best. Per inch, foam has the highest insulating value. If you can afford to lose some headroom, you might consider some of the foil faced foam sheets mounted to the bottom of the joists and gain both radiation and reflective benefits.

    See what the others have to say. Adding fiberglass is doable, but can get messy with a lot of pipes and wiring to get good coverage. You will likely have to split the batts and put part above and below some things. If you compress it too much, you lose a lot of its insulating capabilities.
  3. ussfox

    ussfox New Member

    Messages:
    3
    Location:
    pennsylvania
    Jim,
    Thanks for the info. Are you talking about styrofoam or similar products?
    The basement under the kitchen is partially finished, unheated but used quite often and doesn't get below 65, it has 7 ft ceiling and is surrounded by earth. I prefer not to enclose the whole joist but will if needed. The bubble insulation looks easy to work with but I'm looking for a high r factor.
  4. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,180
    Location:
    New England
    No, I wouldn't use styrofoam, it has one of the lower R-factors per inch. The blue stuff, or the foil faced panels (which are available in 4x8' sheets). Note, if you use foam, for fire rating, you probably should cover it, which is another layer to add. You can buy the (isanocilate sp?) foil-backed stuff in up to 2", which is about R-10 (double-check this). You might get away with 3/8" drywall but if you want a fire rating, 5/8" stuff, which is really heavy to install. That loss of headroom may not be acceptable, so that leaves you with fiberglass. You could probably cut the foam sheets to fit in-between the joists, if things are far enough recessed to allow it, then attach drywall to the joists. Check with your local inspector about uncovered foam...you may need that layer of drywall if you go that way. No problem with fiberglass in that respect.

    There's lots of info out there... http://www.ornl.gov/sci/roofs walls/insulation/ins_02.html
  5. ussfox

    ussfox New Member

    Messages:
    3
    Location:
    pennsylvania
    I found some reflective barrier called "prodex total" that looks pretty good, can go between the joists and won't have to cover it. R value of 15 to 21 depending on the air space. Unfortunately it's a minimum of 700 sq. ft.
  6. patsfan78

    patsfan78 Web Development | HVAC

    Messages:
    33
    Location:
    Maine
    Have you installed a staple up radiant tubing? If so there are certain types of insulation for this scenario. It is installed between the floor joists but it requires a gap (between the tubing and the reflective sid of the insulation) so that the radiant heat waves of the stapled up piping will "bounce" off the reflective foil and head up into the floor. Otherwise you get wasted BTUs.
  7. Dana

    Dana In the trades

    Messages:
    2,932
    Location:
    01609
    If this is a suspended-tube radiant you'll get some benefit out of a radiant barrier, but if it's plated with aluminum heat spreaders in full contact with the sub-floor the benefit is almost vanishingly small. The emissivity of aluminum is EXTREMELY low, and the fraction of radiated heat transfer is miniscule- if there's (nearly) nothing to reflect, the radiant barrier has no function- it'll work about as well as a sheet of poly (or bubblepack). Claims of "R20 equivlent" are completely bogus, based on a totally different ASTM test configuration that is not relevant here.

    The emissivity of the bare wood is much higher, but it's mostly covered with low-e aluminum plates, and even if the heat was all above the floor, the most you'd get out of RB is a ~25% (when very new & shiny) reduction in downward heat flux, since most of the heat loss would still be convected & conducted, not radiated.

    Plated or suspended, you need some sort of insulation that has an R value determined by ASTM C518, a conducted & convected heat transfer block. In hot-side up configurations even low-density unfaced fiberglass batts still do OK, since with the warm side up the induced convection is still quite low. If above a full basement that's reasonably air sealed it doesn't have to be perfect either. It's cheap and (in this case) effective. (DO foam seal the band joist & sill ends of the joist bays, to prevent cross-drafts throuh/above the insulation though.)

    Above conditioned space R11-R15 is fine, but if it's above a cold drafty crawlspace/basemen R19 min. If plated, snug it right up against the plates (but with minimal compression.) If suspended, cut strips of radiant barrier (bubble or aluminized polyester, whatever is cheapest) that fits loosely, resting atop the fiberglass, but hang the insulation as low on the joist as possible, with the largest possible air gap between the RB & tubing. You could cut the RB wide and staple it, but that just adds a lot of labor with minimal benefit.

    Rigid board insulation is about the most expensive way to go, and may be very difficult to install around obstacles. In some installations it's easier (but not usually cheaper) to spray 4-6" of half-pound foam (Icynene, et al) directly to the underside, (but woe to whomever has to repair a leak from an ill-placed flooring nail if you go that route. If you DO go with rigid board stuff, EPS (beadboard) is usually the cheapest per unit R value, and you can get it with single side foil-facer (which is an effective radiant barrier for suspended tube stuff.) You'd need a minimum of 2.5" of EPS or 2" of XPS (pink/blue board) or 1.6" of polyisocyanurate over a decently air sealed basement. Then, in order to meet fire code you'd be required to put a half inch of gypsum between it and the basement (a ceiling) as a thermal barrier to keep the foam from lighting up/creating toxic smoke in a fire situation. (With fiberglass there is no such requirement.)

    Use UNfaced fiberglass batting and PERFORATED radiant barriers, or you run the risk of creating seasonal mold conditions. You want to avoid placing a vapor retarder between the basement and first floor if you don't have to, or else control the humidity in both the basement & first floor to guarantee that the average relative humidity anywhere on the joists stays below 70%. (In summertime 60% RH air at 75F on the first floor exceeds 70% at the point in the insulation where the temp drops below 70F. If there is a vapor retarder anywhere on the basement side of that depth, you have mold-enhancement going on even if you're dehumidifying the basement, since it's on the first-floor side of the hygric zone created by the vapor retarder.
  8. jnyost

    jnyost New Member

    Messages:
    11
    Location:
    Mid Ohio
    I would use fiberglass for several reasons

    1. It's fairly cheap
    2. It's extremely flexible
    3. It can be removed if needed

    The fiberglass will be extremely forgiving as you try to stuff it around things. Fiberglass gains a lot of its R value by the air it traps inside all the weaves. Obviously, you'll loose a little R value with compressing it, but you would loose the R value by pulling it apart too. The only thing you'll need to do is get some wire supports that helps hold it between the joists.

    Btw.... Pay attention to your local ads. Some stores are running sales for insulation.
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