I have a cathedral ceiling with no insulation. Construction is 2x6
pine tongue and groove sitting on 4x10 beams. These beams are spaced 4
feet on center. The roofing material is Cedar Shake. What I would like
to do is install 4" styrofoam sm (R20) between the beams and finish
with pine again to retain the original look. Will I encounter
condensation problems? If so what needs to be done to rectify the
On Sep 1, 11:33 pm, email@example.com wrote:
You need to:
1) Put in a ridge vent, soffit vents, and chutes to connect them.
2) Put in a plastic vapor barrier before you put the tongue & groove
ceiling back up.
Polyisocyanurate will get you better than the R-5 per inch that you
are planning on for the styrofoam.
On Sat, 01 Sep 2007 21:33:40 -0700, firstname.lastname@example.org wrote:
I never had one, and I'm sure there is more than one design, but my
friend has a cathedral ceiling that has a foot or two between the
inside surface and the outside surface. If you have one like that,
shouldn't the insulation be put in the inside, no need for more pine.
He went in their and did something once, but he says he's not going in
again. He's thin and healthy, and could do it just as well as before,
but I don't think he likes this kind of stuff as mmuch as many of the
people here do. And he's 63 and I think you gotta really love attics
to do this at 63.
I assume you are in a cold climate since you mention condensation in a
cathedral ceiling. I would go with polystyrene over polyiso for two
reasons: polyiso can absorb water, so if you do get any condensation,
your foam could get soaked, and second, poly iso isn't much fun to cut
with a circular saw. It is true that it gives you more R per inch. A
difference between the 2 types is that polystyrene will act as a vapor
barrier as it is (in thicknesses over 1 inch),,,polyiso has to have a
foil face or some other coating to act as a vapor barrier.
Your trick will be to get an airtight fit with the foam to the 4x10
(if I am picturing this right). Definitely buy a pro grade foam gun.
Might even be best to leave a gap between the foam and the 4x10 and
fill this with expandable gun foam. Alternately, you could go for a
tight fit, and caulk the foam to the 4x10. You MUST use a flexible
caulk. Acoustical sealant is the preferred product. Also tape the
seams. If you do a good job, a poly vapor barrier is redundant. By
the way, a poly vapor barrier would have to be caulked to the 4x10's
as well, with acoustical sealant. .
Are you absolutely sure there is <NO> insulation? Anything built in 1960s
on up, the common practice was to lay down some sort of fiber panels over
the T&G, then paper and shingle over that. Are there slats or something
under the shakes to keep the back of them dry? How old are the shakes?
I'd get a good roofing contractor in, and price what it would take to
insulate from the outside- pull off the shakes and any low-R fiber panels,
reskin the roof with modern high-R foam panels designed for exterior use,
and lay a new roof surface over that, with suitable flashing and trim around
the edges to make it look right. (My preference would be some sort of
standing seam metal- I hate the upkeep of shakes. If you want the shake
look, they make plastic ones now that outlast wood, and don't rot.)Note that
this would take a roofing company experienced in commercial-grade work, not
the typical residential re-roofer that uses low-buck crews hired from
Unless you give up a foot of headroom, and install a whole 'nother ceiling
system and faux beams below, I don't think there is any good way to do what
you are proposing, and have it come out looking right. Lots and lots of
cracks between warm and cold material, and if condensation happens, lots of
crevices for stuff to grow.
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