What's the best way to insulate cathedral ceiling? Where I live
(central NJ) attic R49 insulation is recomended. I don't see how to
achive this with fiberglass insulation even if using 2 X 12 ceiling
joists. Of cause it is possible to use rigid foam insulation but it
seems to be expensive and also will create thermal bridging where
joists are. I wonder what's the best and optimal way of insulating
cathendral ceiling to required level>
If you are building a new construction, You can use the rigid foam,the
brown Isocyanurate kind is best. You would use the Engineered Truss type
framing material to minimize the bridging.
Thermal bridging? What do you mean. If you mean the difference in R
value Polyurethane or Polyisocyanurate sheet settle at about R 6.5
cured, wood might be R 3.5 per inch or more, I dont see a problem
except you need 8" of foam and spraying would be cheapest, but some
spray foams are only R 5 per inch, some are alot more so you have to
pick and research what locals sell. What is the construction now, you
have shingles, decking, then what. The only thing I think is important
is an air gap to the peak with ridge vent, so roof decking and
shingles dont cook in sun and fail in 5 years, unless you have a
metal, slate or tile roof. But im no pro at this, just learning.
By thermal bridging I mean wood rafters uncovered by insulation. They
have way less insulation then whatever insualtion is in cavity thus
creating thermal bridging. When insulating attic you cross second
layer (ussualy R19) fiberglass insualtion over ceiling joists that
have R30 in cavities thus eliminating thermal bridging.
This is what I got
"The R-value for wood ranges between 1.41 per inch (2.54 cm) for most
softwoods and 0.71 for most hardwoods. Ignoring the benefits of the
thermal mass, a 6-inch (15.24 cm) thick log wall would have a clear-
wall (a wall without windows or doors) R-value of just over 8. "
So ceiling beams are 12" or R 12, there wont be any condensation, that
will occur on less insulated areas if it even happens like on your R
3.3 dual pane glass, Consider fiberglass it looses R value the colder
it gets, spray foam is still the best.
When you don't know the species of lumber, figure an R value of 1 for
You seem to be implying that the framing area is minimal, but that is
not the case. Typical wood framing makes up 10 to 15% of the wall/
roof area. That is not an insubstantial number and definitely affects
the overall R value of the building envelope. If you see any energy
calculation that ignores framing area, it is a faulty calculation - a
How old is the roofing? You could add as much foam board as you wanted
on top of the roof joists then reshingle.
I live much further up north. At the time I built my house the
recommendation was R-40 with rumors of that changing to R-50. I maxed
out and put in R-60. (Parallel chord trusses).
One of my neighbors did the opposite. He put in R-32 at the same time
I did mine. His house costs more to heat than mine and I have 600 sq
ft more. Both houses are one story bungalows with R-20 walls. I also
have close to double the amount of windows that he has. Mine are
triple pane, his are double.
Seems to me that the way energy costs are going additional insulation
is a good investment. It will pay for itself then start putting money
back into your pocket.
Not saying this is what happened here, but lots of people hear something
like "wood is one of the best insulating building material". Yes, this
is true for "building materials". But fiberglass isn't a "building
material". Well anyway I've never seen a house built out of fiberglass
In my last house the attic was finished and it had a low angled ceiling.
Outside it was quite obvious to see the frost or light snow melt in
small strips.... right where there were studs. In between the studs
were it had fiberglass insulation, the heat was better kept in the house
and the snow stayed on the roof.
What I don't get is the nit picking over tiny numbers when just having a
cathedral ceiling is such a big waste of heat in and of itself....Especially
if they are very high.....Yea , I know people love them but they are such a
waste of space and heat....Not to mention how big a PITA it is to change
light bulbs or re-paint ect......I'ld rather have the attic space for
storage or another room or two upstairs..JMHO.........
I do not understand why "cathedral ceiling is such a big waste of
heat" if they are properly insulated and ventilated?
Because of ALL the extra space you need to heat to feel warm at floor
level...Wasted space and wasted heat....
HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.