Now everyone in homerepairlive land is confusing me. I was told by someone
that I could use polystyrene instead of fiberglass to insulate my HUGE
crawl space and it will have and R10 value opposed to the R13 value of the
fiberglass. I first asked the question what does the "R" mean then I asked
is polystyrene (styrofoam) just as good as fiberglass to help keep in
heat. Could someone simply say yes or no. Is polystyrene good, safe and
effective to use for insulating a HUGE crawl space?
The R value will depend on the thickness of the material. Dow Styrofoam
blue board that is 2" thick will have an R-10 value. If you double the
thickness, it will be R-20. EPS bead board is R4 per inch. I have 2 1/2"
in my garage.
Yes, it is a good, safe material. It is treated with a fire retardant
additive to meet building codes. It is CFC free, can be recycled. It does
not support insect or rodents.
Yes, it's good, safe, and effective.
Main issue is whether the crawlspace is reasonably close to being
airtight--if it's well ventilated then insulating it is not going to do
much good--you'd do better to insulate the floor.
If the crawlspace is tight enough to be worth insulating then consider
whether it is likely to get wet--if so then you want something that won't
wick moisture--that would be closed-cell foam, not fiberglass.
You might find
to be helpful.
Not wanting to confuse, but you should understand that any such R-value
implies no air movement past the insulant. Read that: sealed along
edges/whatever. Paper flanges on fiberglass, if properly stapled, do
that. With board insulant, be prepared to custom-fit around/inside
obstacles, and caulk. Been there, done that. Not rocket science- intro
On Thu, 13 Jul 2006 10:07:19 -0500, with neither quill nor qualm,
"R" is the equivalent of one inch of wood for insulation. Most things
are better insulators, foams especially. Mice don't make nests in it
or chew it up much, it doesn't mold and compress into mats when wet
like fiberglass does, and foam is easier to work with.
Yes, many of the foams are. Here are charts you might like:
More info here:
- Sarcasm is just one more service we offer. -
http://diversify.com Web Applications
Interestingly, in a place near where I once lived: birds discovered that they
could pick out holes in beaded polystyrene to make nests. The longer this old
building was there, the more bird nests in the insulation. Had the owner
finished construction and, so, not left the stuff exposed, I suppose the bird
problem would not exist.
Depending on the foam, "animal" problems can be _quite_ bad. I've
even seen carpenter ants shred polystyrene.
Instead of fiberglass, rock wool essentially eliminates moisture
compaction problems altogether and is superior to fiberglass in
every other respect as well.
Careful folks, the OP is probably getting progressively more confused,
because we're comparing apples and oranges.
The discussion is about two almost completely different approaches -
insulating the crawlspace walls versus insulating the floor above the
From a purely practical perspective, these two approaches imply
different techniques - the floor is simplest with batts, because of the
joists - stuff the batts inbetween joists, string chicken wire (not
vapor barrier, nor kraft papered fiberglass, because this would be the
"wrong side" (cold side) of the cold/hot barrier and you'll probably
have moisture problems otherwise), and you're done. The walls are
simplest with foam, because it's flat, and the foam comes in "boards" -
but cutting, fitting and sealing could be PITA.
Foam usually costs more in $ per R per square foot than fiberglass
or rockwool batt in terms of costs of materials.
You usually only use foam where you need to minimize thickness
or when the cost involved in batt installation (eg: having to fir
or stud walls) outweighs the material cost. Then again, depending
on geometry, he likely has a lot less square footage of wall versus
[I'll talk about other alternatives later.]
"R value" is a measure of insulation effectiveness. R20 is
better than R10. 3.5" of fiberglass is R13, 6.5" is R20. Between
joists, you could probably go considerably thicker depending
on joist depth (perhaps as much as 11.5"). Foam boards are
R4-5 per inch. In either case, pick the R value you're aiming
for, and that determines the thickness.
Further, if you compared, say, R10 on the walls versus R10 on
the floor, you'd probably find doing the floor more efficient
because just doing the walls doesn't impact thermal transferance
thru the floor of the crawlspace. In other words, encapsulating
the living space with insulation _directly_ will have more
end-result effectiveness all other things being equal.
How much? Can't tell without seeing it.
There are other considerations. For example, keeping a batt'd
floor dry can be quite an issue in some situations.
To get the best answer, he really should get a few insulation
contractors in to examine the situation and let them do the
calculations to find out which is better.
- fur or stud the walls and use fiberglass/rockwool (tho,
this is likely to be a recipe for mold/dampness problems
with a dirt crawlspace).
- spray foam under the floor (not the teensy cans - this
is not DIY). This has the added advantage of vapor
barriering the floor (on the right (warm) side). Hence,
no moisture problems.
Is this job (wall foam or underfloor fiberglass) DIY? Yes. I've
done both (at least in smaller quantities). But determining which
is _optimal_ (both in cost and effectiveness) probably isn't DIY,
and requires intimate knowledge of the OP's precise situation and
local conditions, neither of which ahr posters know.
Chris Lewis, Una confibula non set est
It\'s not just anyone who gets a Starship Cruiser class named after them.
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