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Insulation for radiant staple up

dinnerbellmel | Posted in General Questions on

Hi, we are building a home in climate 5. The house will have geothermal with radiant heat in the basement slab and the first and second floors. We intend to finish the basement at a future date but not right away. Our contractor was planning to staple up the insulation with aluminum transfer plates and insulate with the foil bubble wrap stuff (thick foam under the basement slab.). I have read a lot about insulation for this type of application and it sounds like the foil bubble wrap stuff has little value.

My question is what do we do about insulating between the first and second floors? Is the foil backed bubble wrap stuff sufficient or should we think about adding some additional insulation between the wrap and top of the ceiling below? A lot of the stuff I read about was how to insulate between the basement and the first floor but I’m not sure of how much insulation is preferable between the first and second floors. The ceiling height is 8 feet and the floor will be engineered hardwood. Thanks in advance!

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  1. Expert Member
    Dana Dorsett | | #1

    Between two heated floors, cheap contractor-roll R13s installed with the fiberglass side snugged up to the heat transfer plates & subfloor (no air gap) works just fine as a cheap & reliable way of isolating heating zones from each other.

    Bubblepack installed with 2"+ air gaps both above & below would work too, but it's more trouble to install, and not particularly a great bang/buck, and would need the basement ceiling gypsum installed to hit it's best performance.. It's generally worth far less than advertised (or charged.) Bubblepack needs at least an inch between the bubblepack the adjacent layers to hit a performance level better than R2-R3, but might hit R8-9 performance with 3" of air above & below, with air-tight gypsum on the bottom side of the joists.

    The most honest & direct explanation of radiant barrier R-value claims I've seen from a radiant barrier vendor is this short video:

    Mind you, he's still saying you'll save money with his aluminized fabric radiant barrier product in your attic, which is a dubious assertion unless your attic is basically not insulated.

  2. user-2890856 | | #2

    The bubble wrap is GARBAGE , plain and simple . The 2" air gap type install Dana remarked about will also REQUIRE high water temps . R 13 is fine , no air space whatsoever . Be sure to also insulate the ends of the joist bays to avoid horizontal heat loss .

    High temp radiant is the worst idea ever . Now , considering that you are doing GeoThermal , low temps become quite a necessity . High temps (above 110*) should be avoided at all costs .

  3. Dana1 | | #3

    The 2" gap both sides doesn't require high temp radiant to hit that comparative R8-R9 performance, but the rest is pretty much true. The ASTM C518 test would be roughly a 25F delta between the shiny stuff and the subfloor, and a a 25F delta between the temp of the ceiling gypsum & bubble pack, 50F total. With a non-heated 50F basement and a 100F heat spreader plate you'd be looking at something like 110F water. Even if the basement were 60F and the subfloor was 90F, it would still perform in about the same range.

    The best use for bubble pack in a home is between a high-temp steam radiator and the wall in a rented home where you don't have the option to do much better. It'll make a difference that pays for itself in that application, provided you can find it in quantities that small. I've also seen it used to good effect wrapping pallets of cases of wine in multiple layers for long haul shipment by non-conditioned trucks. (A high value cargo that can be damaged by temperature spikes, damage that can be avoided by a modest amount of insulation, given the high thermal mass of the cargo.)

    It's nice and shiny though- isn't that enough?!! :-)

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