I am adding another 3 1/2 inch insulation layer under the floor of my
utility room, which is cantilevered out from the house, with a 4 foot
breezeway underneath. It is an unheated area that I want to reduce the
temperature swings since it has three exterior walls. Between the floor
joists there is currently 3 1/2 inch R11 with foil facing on the "up"
(subfloor) side. I have enough craft-backed R13 3 1/2 inch to do the job,
but am uncertain whether to orient the craft backing in the up or down
orientation against the existing batts, or do I have to remove the backing
and use some sort of wire to hold the insulation in place?
If you already have craft-backed fiberglass insulation that you're
installing over old batts, you want to remove the craft paper from
either the old or the new. If the craft paper is against the opposite
surface, remove the craft paper from the new. If the craft paper is
facing you, remove the craft paper from the old. Actually, you don't
need to remove it, perforating it (so that vapor can go through it) is
just as effective. There's a little roller thingy with pointy spikes
on it that can be used to do that, sorry that I don't remember the
name of it, it's been many years. Anyhow, the point is that you don't
want two vapor barriers there, because vapor will build up between
them and condense in the insulation.
Eric Lee Green mailto: firstname.lastname@example.org
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