Hello, I am re-finishing an attic in an older home in Ohio. I have
removed all of the existing walls and insulation. I am down to
rafters and I am now ready to start the project. I would like to
insulate the attic the best way possible as prior to the remodeling it
used to get pretty hot up there in the summer. I have 6" trusses with
about 5 1/2" available space between the roof sheathing and the living
space for insulation. The house has 2 gable vents but does not have
soffit vents, but I am going to put them in. I was going to put those
styro rafter vents starting at the soffit vents through the section of
the roof that is the angled ceiling of the finished space, but they
are a whooping 1 1/4" thick which really reduces my space for
insulation. While wondering in the home improvement store I came
across reflectix radiant insulation. My idea now is put the styro
rafter vents at the soffit vents to keep the blow in insulation on the
floor of the attic from blocking the air flow. I was then going to
staple relflectix between rafters starting at the bottom of the
section that is the angled ceiling, up over the top flat area and then
down the other section of truss that is the angled cieling on the
other side. I plan on doing this leaving a gap of 3/4" between the
reflectix and the roof sheathing in the sections that is the angled
cieling. I am then going to shim out the rafters with 2x2s and add 5
1/2" thick high density unfaced R-21 insulation between the reflectix
and the inside edge of the living space. I plan to finish it all off
with a poly vapor barrier. This should give me about R-30 for the
attic space. Does this sound like a good setup? Is it ok to put
fiberglass under radiant insulation such as reflectix in roof trusses?
Am I going to have any moisture problems? I would think that
reflectix is a 100% vapor barrier so it sounds like I'll have a double
vapor barrier with this setup? Is that a problem? I am thinking this
is ok because those styro rafter vents would also act as a vapor
<< While wondering in the home improvement store I came
across reflectix radiant insulation. >>
Just wondering, if this is installed with the reflecting surface up, will it
cook the shingles? Maybe there's enough airflow from soffit to ridge vent just
under the decking to keep things cool on the roof top?
email@example.com (Daniel Rubin) wrote in message
One suggestion would be to add 2x4s underneath the existing 2x6
rafters to make an actual depth of 9 inches. Definitely use the
spacer baffles on the underside of the roof deck to provide continuous
ventilation from the eaves to the ridge. This will give you 7-3/4
inches of space, so you'll be close to R-30 if you use R-30 fiberglass
batts intended for 2x10 rafters.
If you don't already have a ridge vent, install one, or use some of
those roof mounted vent caps.
One thing I'm thinking about doing in our semi-finished attic, but
haven't researched yet, is to put in unfaced fiberglass as described
above, and then add a layer of rigid foam underneath that. There
would be two benefits to the rigid foam, it would add R-value, plus it
if it was continuous, it would be a thermal break between the drywall
and the rafters. Then the drywall would be installed on the rigid
foam. But like I said, I haven't researched this yet to see if it
really makes sense or if I'm missing something.
Of course with all of this, you will lose headroom under the sloped
portion of the ceiling.
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