Hi all. I've read through countless posts on this topic but haven't
yet come to a worthwhile conclusion. Here's my scenario:
I live in central Maine - where it gets pretty cold.
My attic has around 3-6" of blown-in insulation - without a vapor
I'd like to improve my situation by adding new insulation.
Can I use fiberglass batts (without vapor barrier) on top of the
blown-in insulation without making things worse?
Should I use fiberglass batts over the blown-in insulation?
Should I add more blown-in insulation over what I have?
Should I remove the blown-in insulation all together and install new
fiberglass batts with a vapor barrier?
I've got serious ice-dams that build up in the winter and I know it's
because of the limited insulation I have in my attic.
You are way under insulated for maine.
I would collect the blown in stuff and
use it but make the depth at least
12 inches deep. where you removed
the blown in stuff, put in paper
backed insulation between the joists
Then add a layer without paper cross
wise to those layers...I did that with
my house and that gives me 1 foot
of batt insulation, I forgot the R value
I ended up with...
Given that ice dams are caused by the snow melting over the heated area,
then refreezing over the eave area, it is vital to keep the area
ventilated to allow the underside of the roof to stay cold. So in
addition to more insulation to keep your heat in, be sure you have
adequate ventilation so whatever heat does get through escapes. Around
our area, ridge vents are recommended, but I always wonder how effective
they can be when snow piles up on them. The snow does melt there first
so it looks like the heat is escaping when it can. But this is not Maine
so you probably have a different set of problems for venting.
I'd say the proper way would be to remove the blown in (only because
it has no vapor barrier), and roll out kraft faced batts between the
joists. Then roll unfaced perpendicular to the joists. I'd go to at
least R-49 (you can find out recommendations for your area on the web;
I don't care to take the time; around MD, R-49 is recommended by some
agency or another (though less is required by code), so I wouldn't go
any less. Attic insulation is way more important than wall so go as
high as you can.
Oh, you can resue the loose stuff in some fashion also, though it may
be a pain to mix it with the other stuff. I'd use it as additional to
what I've described rather than instead of.
On 14 Aug 2003 12:09:30 -0700, email@example.com (pjoMofo)
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