EcoRenovator - View Single Post - Fiberglass R-value loss in cold weather - R-value drop quantified

Daox · 09-14-09, 03:50 PM

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?

09-14-09, 03:50 PM	#1
Daox Administrator Join Date: Aug 2008 Location: Germantown, WI Posts: 5,525 Thanks: 1,162 Thanked 374 Times in 305 Posts	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? __________________ Current project - To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts. To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts. & To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.