polystyrene vs fiberglass

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?
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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.
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cece e. wrote:

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 <http://www.eere.energy.gov/consumer/your_home/insulation_airsealing/index.cfm/mytopic620> to be helpful.
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--John
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cece e. wrote:

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 physics.
J
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On Thu, 13 Jul 2006 10:07:19 -0500, "cece e."

R13 is much more efficient than R10.
What is confusing about that?
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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: http://hes.lbl.gov/hes/makingithappen/no_regrets/insulationcomparison.html
http://www.p2pays.org/ref/08/07361.pdf
More info here: http://www.buildinggreen.com/auth/article.cfm?fileName 0101a.xml&mid
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Larry Jaques wrote:

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.
Mike
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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 crawlspace.
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 floor.
[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.
Other options:     - 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.
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Chris Lewis, Una confibula non set est
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