Rhone
Minister of Fire
- Nov 21, 2005
- 827
Well, I'm not really sure about the loss of R-Value or that it only applies to fiberglass if true. The examples, one comes from a foam company the other from a quick look talks about loose-fill fiberglass which... loose fill fiberglass is just the junk of the industry, very little in common with fiberglass batts. Don't worry Precaud, you're on the right track and don't Warren about your walls, the issues of fiberglass batts don't apply much when they're installed vertically. In my energy books, fiberglass gets mentioned repeatedly as a bad choice for attics and floors for one reason or another, but those same authors say the problems that plague them don't apply much when they're used in walls, and they use it there themselves.
My new energy book this year went extensively into fiberglass batts, studies, and results and says fiberglass batts in most cases is acting around 50% but can be worse. Here's a brief synopsis (when installed horizontally). First, to get the full R-Value it needs to be installed to the book, and I've seen reports say when fiberglass is installed too the book it has the same air penetration properties as blown. But, we need to define what's too the book? Ready for this? Each piece/roll has to be "fluffed" to the height it's supposed to be. Then, each piece is supposed to be fit with surgical precision, absolutely no gaps and tight but not too tight. The corners can't be bent up/down or rounded, if going between studs/joists the sides need to be pushed down with a putty knife and pulled back out to ensure the sides are "square". All pieces must be fit tight together, any obstructions need to be cut around the obstacle to maintain a 0% gap (so that it fits like a glove), and can't be compressed. The penalty of failing to do such, is astronomical. My books show just a 1% gap around fiberglass batts will reduce its effective R-Value almost 50%, but it depends on the starting R-Value. The higher the R-Value of insulation the worse the effect. That is, a 1% air space around an R38 batt will reduce its total performance to act more like R20 whereas a 1% air gap around R13 batt will reduce it's performance to be more like around R9-R10. Tomorrow I'll take a picture of the page in my book that shows the chart of just how much R-Value you lose with fiberglass batts with how much air space. Since joists aren't a perfect 16" or 25" O.C., since it's not possible to make glove-tight cuts around obstacles, fiberglass will never reduce airflow or insulate as well as blown cellulose and probably most homes with fiberglass batts in the attic are almost all acting more like 50%-60% what they think it's doing (which the book says also). On the contrary to fiberglass which is nearly impossible to install it correctly to get the full R-Value, blown it's nearly impossible to improperly install it to not get the full benefit. Aren't you glad you went with the blown?
I just finished installing insulation in my attic, I picked fiberglass batts because I'm not done remodelling and wanted the ability to move it out of the way and put it back. So, I methodically fluffed, carefully placed each piece checking repeatedly no spaces, any obstacle I went around (instead of trying to cut the shape out of the batts) and afterward filled the hole with blown cellulose by hand. There's no way I'd picked fiberglass batts again, it cost me probably 3x more, took me 10x longer, and I probably have about 80% of the R-Value since I was so careful. I'd been better off to walk and destroy the cellulose when it came time for remodelling, and simply fill in the damaged area again with more by hand.
There is what I call a useful insulation limit. Everytime you double the R-Value you cut your heat loss in half. R1 cuts your heat loss by 50%. R2 cuts it down to 25%. R4 cuts it down to 12.5%. R8 cuts it down to 6.25%, R16 to 3.13% as you can see each time you double your R-Value you cut down your heat loss by 50% each time. But by the time you hit R38 you've cut it down to 1%. Bringing it up to R98 you're still at 1%. For example R60 cuts your heat loss by 0.48% over R38. You have to figure out, is it really worth paying for almost twice the material to reduce your heat loss by 0.48%? In my case (house & environment), with Electricity it certainly is. Heating with wood, after 9-10 years it'll save me a cord, I didn't do it.
My new energy book this year went extensively into fiberglass batts, studies, and results and says fiberglass batts in most cases is acting around 50% but can be worse. Here's a brief synopsis (when installed horizontally). First, to get the full R-Value it needs to be installed to the book, and I've seen reports say when fiberglass is installed too the book it has the same air penetration properties as blown. But, we need to define what's too the book? Ready for this? Each piece/roll has to be "fluffed" to the height it's supposed to be. Then, each piece is supposed to be fit with surgical precision, absolutely no gaps and tight but not too tight. The corners can't be bent up/down or rounded, if going between studs/joists the sides need to be pushed down with a putty knife and pulled back out to ensure the sides are "square". All pieces must be fit tight together, any obstructions need to be cut around the obstacle to maintain a 0% gap (so that it fits like a glove), and can't be compressed. The penalty of failing to do such, is astronomical. My books show just a 1% gap around fiberglass batts will reduce its effective R-Value almost 50%, but it depends on the starting R-Value. The higher the R-Value of insulation the worse the effect. That is, a 1% air space around an R38 batt will reduce its total performance to act more like R20 whereas a 1% air gap around R13 batt will reduce it's performance to be more like around R9-R10. Tomorrow I'll take a picture of the page in my book that shows the chart of just how much R-Value you lose with fiberglass batts with how much air space. Since joists aren't a perfect 16" or 25" O.C., since it's not possible to make glove-tight cuts around obstacles, fiberglass will never reduce airflow or insulate as well as blown cellulose and probably most homes with fiberglass batts in the attic are almost all acting more like 50%-60% what they think it's doing (which the book says also). On the contrary to fiberglass which is nearly impossible to install it correctly to get the full R-Value, blown it's nearly impossible to improperly install it to not get the full benefit. Aren't you glad you went with the blown?
I just finished installing insulation in my attic, I picked fiberglass batts because I'm not done remodelling and wanted the ability to move it out of the way and put it back. So, I methodically fluffed, carefully placed each piece checking repeatedly no spaces, any obstacle I went around (instead of trying to cut the shape out of the batts) and afterward filled the hole with blown cellulose by hand. There's no way I'd picked fiberglass batts again, it cost me probably 3x more, took me 10x longer, and I probably have about 80% of the R-Value since I was so careful. I'd been better off to walk and destroy the cellulose when it came time for remodelling, and simply fill in the damaged area again with more by hand.
There is what I call a useful insulation limit. Everytime you double the R-Value you cut your heat loss in half. R1 cuts your heat loss by 50%. R2 cuts it down to 25%. R4 cuts it down to 12.5%. R8 cuts it down to 6.25%, R16 to 3.13% as you can see each time you double your R-Value you cut down your heat loss by 50% each time. But by the time you hit R38 you've cut it down to 1%. Bringing it up to R98 you're still at 1%. For example R60 cuts your heat loss by 0.48% over R38. You have to figure out, is it really worth paying for almost twice the material to reduce your heat loss by 0.48%? In my case (house & environment), with Electricity it certainly is. Heating with wood, after 9-10 years it'll save me a cord, I didn't do it.
Enjoy
