Fiberglass R-value loss in cold weather - R-value drop quantified
 

I just wanted to discuss this and get some info floating around here on it. It has been mentioned a number of times here that fiberglass looses its r-value in cold weather.

Today, I found this article that actually quantifies the extreme loss of r-value as temperature drops. This article shows that fiberglass will loose up to 50% of its r-value if the temperature differential is high enough! In contrast, it shows cellulose actually raises in r-value as the temperature differential increases.

FOAM-TECH: Building Envelope Theory - R-Value Drift


Through my reading, I have heard this is mainly from air convection through the insulation. The cold air drops and warm air rises right through the insulation itself. Cellulose is apparently much better at blocking air flow through itself than fiberglass. So, I'm sure closed cell foam would be even better.

Here is another article that goes into detail a bit more.
Convective Loss in Loose-Fill Attic Insulation


The one thing that these articles don't address is batt insulation. Each article specifically addresses the fiberglass as loose fill fiberglass. Are the same problems there with batt insulation?

Reading stuff like this makes me want to develop evacuated containers for building insulation.

Is cold air a better insulator than warm air? (Because of air density...)

I would imagine warm air would be better because of density. There will be less conduction of heat if the molecules (of whatever) are farther apart. This would make your evacuated containers the best thing available.

I would imagine that the same effects would occur, because even with foil faced, there still is a gap at every edge for air movement. I have read that putting cellulose over the top of fiberglass insulation prevents this problem

Insulation Tests & Reflections...
 

About 15 years ago I built a test rig which was incredibly simple... I took a 5 gallon bucket, made a small pedestal upon which my test sample would be placed, and heated to boiling, an aluminum beer can of water.

I placed insulation in question below, and beside the sample.

The test was conducted in my living room, so the temp was always the same.

I would place the sample into the test rig, put a thermocouple in the water, place insulation over the sample, put on a lid with holes (there were also holes in the bottom of the bucket) and take data at regular intervals, for an hour.

I had no way to quantify the materials, but I could get a ranking of materials
when I plotted the heat loss data.

The ranking agreed with the study you cite.

Cellulose = best

Fiberglass = middle

Styrofoam peanuts = worst (recycling maniac = me)

However, when I mixed small-particle styrofoam chunks in with the peanuts to fill the voids, it ranked with cellulose. So yes, air migration was the villian.


There's also an R-value creep regarding polyurethane foam, if compared to expanded poly-styrene. Funny, the study didn't mention that in the study. Possibly it's because they (Foam-Tech) sell the polyurethane foam.

The polyurethane foam has a higher initial R-value (and cost) but over time (15 years or so) it's R-value falls, because it takes up moisture, to about the R-value level of EPS (expanded poly-styrene).

So initially, polyurethane foam is the R-value winner, but over time, EPS becomes the 'R-value per dollar' winner.

Best Regards,

-AC_Hacker

Do you have a link to the study done on that?

Well, I used to find this info easily, but it's not easy to find now. Possibly, there have been changes to the product to remedy this situation, possibly there was a threat of lawsuit.

However...

• Here is product info in EPS.
  
• Here is a page that seems to address the moisture effect of insulating foams.
  
• Here's another...
  
• Here's a patent that seeks to cure the moisture absorbancy tendency of polyiso...
  
• Here's a book that addresses Water vapor transmission through building materials
  
• Here's a paper on Water vapor transmission and moisture accumulation in polyurethane

I hope this helps...

Best Regards,

-AC_Hacker

Interesting, but a bit contradictory. Your third link says that foil faced polyiso is 22 times better at blocking moisture than XPS.

I'll have to do some more digging. I'm sure there are problems, but getting data that says polyiso from the extruded polystyrene foam association doesn't seem like the most unbiased source, haha. They did source an Oak Ridge National Lab study, but we have no way of knowing the conditions of that test.

Thanks AC Hacker.

The ranking agreed with the study you cite.

Cellulose = best

Fiberglass = middle

Styrofoam peanuts = worst (recycling maniac = me)

However, when I mixed small-particle styrofoam chunks in with the peanuts to fill the voids, it ranked with cellulose. So yes, air migration was the villian.

[
Hi There, im brand new to the forum and am happy i found.

I found this little bit very ienteresting, as I can get laods of styrofoam particles (from a styro board cutter) and was thinking of using it as garage insulation. I was wary, not having any information as to how effective it would be.
You tested a mix of peanuts with particles. did you ever test just the styrofoam particles alone?

Pierre

Energy Savers: Polystyrene Insulation Materials
this link from EPA states loose fill styro has an r-value of 2.3 per inch. isnt that quite a bit lower than cellulose?