insulation sheets foiled backs


What does this insulation serve? I see some at The Home Depot. Regulation? Heat reflection? Some fire protection? or all of those reasons?? I want to put some on the basement walls over cinder block, foil out.
g
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The foil backed insulation is a superior product and gives you more insulation (R-value) both per dollar and per inch by my calculation than other similar products. The foil itself not only has insulation value but also acts as a reflective vapor barrier.
If you use two layers of foam board they can be staggered so that the barrier is continuous. I like it also because it is less likely to be damaged when transporting or installing compared to regualar foam board.
It seems more expensive at first but when you consider performance you come out ahead. The only reason to use unfaced foam board is if you really need a lot of total R value like a roof. It comes in larger thicknesses and so a given R can be acheived with fewer sheets.
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I don't think the foil is thick enough to count as fire protection. This is my guess, one it is reflective of heat, and two, it keeps the foil together from small bumps and scratches.
Just a guess......
tom @ www.FindMeShelter.com
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zek wrote:

The foil offers 0 fire protection and insulation, but it does offer some heat radiation resistance and it is a vapor barrier.
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Joseph Meehan

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Au contraire, it offers some real (vs code :-) fire protection, and the ASHRAE HOF says it adds a real US R2.55 when installed vertically with horizontal heatflow and a 3.5" air gap (exposed toward the room) and a 50 F mean temp and a 30 F differential, eg 65 F room air and a 35 F basement wall.
Nick
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On Feb 5, 3:25 pm, snipped-for-privacy@ece.villanova.edu wrote:

I'm getting some good answers. I was thinking the foam was allready a vapor barrier, but I could be wrong. Its funny, foiled drywall can also help get rid of excessive RF radiation from local towers, etc., if used in a continuous manner. Not perfect, but can be used effectively.
I measured my basement wall, an above ground section, when the outside temp was about 10, the interior cinder block wall was about 43 degrees. I went around over the weekend, and must have sealed up a large area up around where the block meets the wood. Most of the area in the basement was leaking, the way they built it. Its a 50's home. Luckily the upstairs walls were insulated with mineral wool batting. I added insulation in the attic before winter. Been sealing joints since its got to be 0 deg. here.
g
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snipped-for-privacy@ece.villanova.edu wrote:

That is more a function of the air gap than the foil. The foil itself is very very small.
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With no foil (e = 0.82 vs 0.05) the air gap only adds R0.91 vs R2.55.
Nick
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snipped-for-privacy@ece.villanova.edu wrote:

Unless I am remembering my physics classes wrong, we have an apples and oranges calculation. I stand by my opinion that in the situation described by the OP the air gap is more important than the foil in real life.

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Joseph Meehan

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I'm afraid these real real life measurments prove you are wrong.
Nick
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In what sense? Conductances add, and Table 2 ("Thermal resistances of Plane Air Spaces") on page 22.2 of the 1993 ASHRAE HOF says the total airspace conductance is the sum of the conduction-convection conductance Hc and the radiation conductance EeffHr, which is the emittance (eg 0.05 for a single foil and 1 for a non-foil) times a linearized radiation conductance, 4sigmaTm^3, eg
20 L=.5'air space (inches) 30 TMP'mean temp (F) 40 HC=.159*(1+.0016*TM)/L'conduction-convection conductance (Btu/h-F-ft^2) 50 FOR EEFF=.05 TO 1.01 STEP .95'effective emittance 60 EEFFHR=.00686*EEFF*((TM+460)/100)^3'radiation conductance (Btu/h-F-ft^2) 70 C=HC+EEFFHR'U-value of air space (Btu/h-F-ft^2) 80 R=1/C'US R-value of air space (ft^2-F-h/Btu) 90 PRINT EEFF,HC,EEFFHR,R 100 NEXT EEFF
emittance Hc EffHr R-value
.05 .34344 0.045499 2.571095 with one foil 1 .34344 .909986 .797814 with no foil
The total R-value of the airspace is the reciprocal of the total conductance. With a foil, the conduction-convection conductance does not change, but the radiation conductance goes down, so the R-value of the airspace goes up by a factor of 3 or so, from about 0.8 to 2.6.
Nick
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first read about the project at: http://www.buildingscience.com/resources/foundations/Basement_Insulation_Systems-2002.pdf
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I read this, and you may have referenced this to me before. I didn't think completely covering the wall was a good idea, except one of my walls is mostly above ground. Thats the one that gets the coldest. The other walls, are just going to be covered half way down, with a good sized air space between the future drywall.
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There is one type of foam thats best for fire, but it still recommends sheet rock protection. I think I need some type of rigid fiberglass, but don't know where to look for it around here. It also seems to me that foam placed on top of cinderblock is partially protected just because it sits on top. i found cinderbloc like mine is about R3. I went in two suppliers around here. The foam boards appear to have different R values. Some give R3 at 1/2 inch, then R3 at 1 inch.
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