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Mike said -
I'm skeptical about the TekFoil. Radiant
barriers work best for radiant flow. We're primarily concerned about the
conduction losses from the slab to the ground. Plus, I don't understand
how the installer could specify this product when he just got just saying he
doesn't want to use poly. I suspect the bubble wrap and foil sandwich
probably has a perm rating as low of the poly. Why would it be ok if the
poly isn't (of course, the poly is ok. I'm just wondering about what
appears to be a logical inconsistency.
Frazer says -
It was me that said NO poly, based upon Lstiburek's
argument that the slab should be able to dry to both the inside and
to the outside. It is the radiant installer who wants poly &
TekFoil. SO I think he is confused - 1) TekFoil is a vapor retarder,
2) it's function is radiant barrier and 3) for the same cost, he ought
to be recommending another 2" of rigid foam.
PS: Isn't Dow board (or the pink or green stuff)
vapor permeable or semi-vapor permeable and since moisture vapor flows from warm
to cold, isn't poly, possibly as Lstiburek says, 'counterproductive'
??
-------------------------------------
Frazer
Dougherty
North Fork Retrofit & Solar Options
Mail: Box 4016, East
Hampton, NY 11937
Shipping: 75 Industrial Rd, Wainscott, NY
11975
tel. 631.537.1654
fax. 631.537.1637
cel. 631-645-3534
www.home-performance.org
www.solaroptions.com
Insight '00
#1048, citrus yellow, 61.1 lmpg
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