Is there such a thing as too much attic insulation? I have R38 in the attic
at the moment, but the local building inspector says they like to see at
least R50 in new homes. Would adding another layer of R38 (total R value
would then be R76) perpendicular to the existing layer of fiberglass be
overkill? Or will it make a difference? Does attic insulation really cut
down on heat gain in the summer and heat loss in the winter? Or is there
some other place to look to cut down on heat gain?
When I put in the first bat of R38 I checked and there is no vaper barrier
anywhere. It goes something like this: ceiling wallboard (1/2 inch thick),
ceiling joists (2x4), 2 -3 inches of probably rockwool insulation (at least
35 years old) between the joists, R38 bats of insulation laid perpendicular
to the joists to cover them.
The first layer is unfaced and I was planning on purchasing unfaced again.
Is the lack of a vaper barrier a problem?
A good paint job on the ceiling below acts as a vapor barrier.
Especially with a "vapor barrier" rated paint. Ask about it
at a good paint store. HD _might_ carry such.
R38 is nothing to sneeze at. Going to R76 would be overkill methinks,
and not going to make much difference over something slightly more
modest. I have seen a modern house done to R70. Almost scary ;-)
If you're doing this for a sale, it might be worth it. If anybody
A single layer of 3.5" (R16) would be easy, cheap, and get you to R54.
By the time you're at that level, other issues will end up being
the biggest losses.
A house that started with 3-4" of rockwool (about R16.5 with
modern rockwool, probably somewhat less with older stuff) is going
to need attention to other things before going to R76.
Chris Lewis, Una confibula non set est
It\'s not just anyone who gets a Starship Cruiser class named after them.
On 14 Jul 2006 19:05:20 -0700, email@example.com wrote:
I went from damaged/settled original r30 to r60(layed r30, unfaced
batts), and my bills are low enough to brag to my friends about. They
really don't want to work with fiberglass, but today's fuel costs will
change that. ;)
tom @ www.Consolidated-Loans.info
That depends. If you aren't concerned with cost, then no. However, since there
are diminishing returns, at some point, adding insulation beyond a certain point
is not cost effective. That point is dependent on what future energy costs are.
If the only insulation is in the attic, then all you are doing is losing
heat/cool through the walls and basement. As well, too much airflow through the
walls, doors, windows etc makes the attic insulation ineffective.
The optimum is to balance it all out. You have to ensure that you have
insulation in the walls and basement as well. Your windows and doors should not
leak air excessively. Ditto walls and such. If you restrict air flow too much,
you should then look at a heat recovery ventilator to ensure proper ventilation
of living space without heat/cool losses.
In general, retrofitting an older house to the max is very expensive and not
always worth the trouble. Sometimes something as simple as a few tubes of
acoustic caulking is very cost effective - close up the biggest air leaks. You
have to investigate all the options and decide when the cost exceeds the benefit.
Doing a heatloss calc is not that difficult. I would say that r76 is
overkill, but what if oil hits 5 bucks a gallon?
in general, with good windows, you still lose half your heat out the
windows, more or less. Around half the remaining goes out the roof[both
because of square footage and heat rising]
Look up heat loss calcs on the web, it is an interesting exercise if
You can estimate pretty damn close
My blind screaming 2 minute guess on a 20x40 little ranch with
walls/window/ceiling of r19/3/38 loses over 16 percent of its heat
through the roof, not counting differences in heat movement, so that
means the most you could gain would be $111/1000 spent heating, and
probably more like half that. But if oil went from 2.50 to 7.50 a
Is it overkill, well my R110 attic was worth every penny. In zone 5, I
had a yearly Ng bill of 460 for 1800sq a few years ago. Mine has settled
to R70 it is fiberglass bats. If you are zone 8 or less R 70 + is a
good idea. Standards are outdated, insulation is cheap compared to Oil.
I had a load calc done , 1800sq ft and only 50000 btu.
The more the better. As noted you should not add a vapor barrier.
After so much additional there are diminishing returns, but it would appear
for the comments of the building inspector that you live in an area where
the extra would be a good idea.
I don't know exactly what I have, but I know I doubled what the builder
put in 12 years ago.
Read an article today on blown in foam insulation. 90% of benefit is
covered in the basic application (i.e. r38 for attics), adding 50% more
gets an extra 5% of benefit, adding another 50% more gets an extra 2.5%
Plus there are articles a plenty that describe what happen INSIDE
fiberglass insulation in cold climates. R76 drops to R25!!!!
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