Posted By oceanstatetuning on 14 Jan 2014 04:10 PM
So I found a HUGE roll of foil faced Bubble Insulation in the attic of my garage. It is 4' Wide and the roll is about 2 foot thick so there must be 100' or so, It might be enough to do my attic. BUT I see it done a few ways. I see some people put the insulation down each side touching/taped to each other and then some people leave a space between the two sides. What is best method in using this product? I have vents on each side of my attic walls and my Attic floor is insulated with batt/blow in.
There are a dozen things wrong with installing bubble-pack RB in an RI attic, but the main one is:
It's a powerful vapor barrier, on the "wrong" side of the insulation for your climate, and create pretty severe moisture issues where none existed before. If you have both soffit-to-ridge venting as well as gable vents you could get away with installing in on your rafters, but never
EVER on the attic floor. If you don't have the soffit-to- ridge venting you can still install it on your rafters, if you stop a foot or so above the floor insulation, and at least 6" down from the ridge to allow the roof deck to still convection-dry into the attic space.
From an energy savings point of view it's not even worth your time to install it if you have at least R38 (10-11" of low density fiber insulation) at the attic floor. It will actually INCREASE your heating season energy use by a tiny amount by lowering the attic temp during the shoulder seasons (the roofing acts as an unglazed solar collector- good during the heating season, not during the cooling season), and peels a tiny bit off your peak cooling load. Your primary cooling load factor is going to from the windows (particularly the west-facing windows), not the attic.
The best use for the stuff in a New England climate is as a retrofit duct-wrap on heating/cooling ducts- give it 3 layers and you'll be at about R6.