Got up in the attic the other day looking for a roof leak and realized the lack of any real insulation.
Basically I'm asking, should I go ahead and shoot for R-60 depth with insulation in the attic, or does it reach a point "not really doing much more."
Thoughts?
if you dont have much then yes, it will help. particularly in winter, but there is in fact a point of diminishing returns where each additional inch of insulation will reap fewer and fewer dollars saved. for household systems i think mid 30's r value is usually about as good as it will get unless you have very well sealed windows, doors, pipe penetrations, and the like. houses tend to be built a little leaky. your milage may vary......
instead of the extra thickness, id definitely spring for something other than cellulose though if i could. it tends to compact over time and looses its effectiveness. especially with leaks in roofs and resulting humidity in the attic.
Cellulose works much better than fiberglass over the long haul. The one exception is that it does compact more than fiberglass with a leak.
R-mid 40's is about the point of diminishing returns but it it's cheap enough then blow till your heart's content.
cellulose is a LOT nastier than the newer fiberglass products. Very dusty and no less itchy has been my experience. I have a thin layer (barely covered the joists) of cellulose on my attic and I topped it up to R60 with "attic cat" blow in fiberglass.
I bought the insulation from home depot and they threw in the rental of the machine. I went from Rnot much to R60 in about 2hrs with me in the attic spraying the stuff in and my dad feeding the machine.
Total outlay to bring the attic of my 2 storey 1800 sqft house to R60 was less than $300 and one afternoon of my time.
I've crawled through LOT'S of attics. Unless the "New" fiberglass is really different from the yellow and pink varieties, I would much prefer the cellulose. It is not inherently dangerous, will not hurt your lungs, and itches much less. But, I was not standing in an attic hatch with a blow gun, I was crawling through it. Big difference.
I've messed with it for 40 years now and there's no fiberglass that compares to cellulose. In Rfactor or mess.
Hang on- there may be other reasons for a preference, but R-value is not one of them. Both cellulose and fiberglass have R-values of 3.2- 3.8 per inch.
SVreX wrote: Hang on- there may be other reasons for a preference, but R-value is not one of them. Both cellulose and fiberglass have R-values of 3.2- 3.8 per inch.
"The R values between blown in cellulose insulation and fiberglass insulation are the same but the thickness varies. On average, blown in cellulose insulation is 2-3 inches thinner than fiberglass insulation when both have the same R values."
http://www.rvalue.net/page5.html
"If a fire occurs, the blown in cellulose insulation, combined with its fire retardants, can slow the fire from spreading and can create a "2-hour firewall". Scientists at the National Research Council of Canada report that, blown in cellulose insulation increases fire resistance by 22%-55%."
"Fiberglass insulation is inert, ages well and is extremely difficult to ignite. However, once fiberglass insulation has been ignited, it may burn fast, hot and could emit toxic gases. Also, fiberglass insulation should be kept away from, light fixtures, chimneys or exhaust flu's to reduce heat build-up and potential fire hazards."
cwh wrote: I've crawled through LOT'S of attics. Unless the "New" fiberglass is really different from the yellow and pink varieties, I would much prefer the cellulose. It is not inherently dangerous, will not hurt your lungs, and itches much less. But, I was not standing in an attic hatch with a blow gun, I was crawling through it. Big difference.
My attic is my only experience with cellulose and I found it to be very dusty and dirty. Maybe it's my tolerance to fiberglass, but the bat and blown in stuff I have added to my house were less bothersome to me then the lung and sinus cavity full of dust I ended up with every time I had to crawl up there.
I don't itch from the pink bats or the attic cat. I insulated two rooms in my house in shorts and a t-shirt - yes I wore a dust mask. Now drilling holes in fiberglass reinforced Hoffman boxes is a different kettle of fish. That stuff is crazy itchy.
Dust mask and goggles are your friends with any insulation. 2 hours of working with fiberglass batts had my eyes burning for nearly 2 days. Goggles for the rest of the project fixed the problem. My attic is R43.
No matter which insulating material you use they all get dusty over time.
If you want your existing house to comply with the laws of the land for building a new house, you can use ResCheck ( http://www.energycodes.gov/rescheck/ ) to verify how much insulation you'd like.
carguy123 wrote:SVreX wrote: Hang on- there may be other reasons for a preference, but R-value is not one of them. Both cellulose and fiberglass have R-values of 3.2- 3.8 per inch."The R values between blown in cellulose insulation and fiberglass insulation are the same but the thickness varies. On average, blown in cellulose insulation is 2-3 inches thinner than fiberglass insulation when both have the same R values." http://www.rvalue.net/page5.html "If a fire occurs, the blown in cellulose insulation, combined with its fire retardants, can slow the fire from spreading and can create a "2-hour firewall". Scientists at the National Research Council of Canada report that, blown in cellulose insulation increases fire resistance by 22%-55%." "Fiberglass insulation is inert, ages well and is extremely difficult to ignite. However, once fiberglass insulation has been ignited, it may burn fast, hot and could emit toxic gases. Also, fiberglass insulation should be kept away from, light fixtures, chimneys or exhaust flu's to reduce heat build-up and potential fire hazards."
R-value per inch does not change. Installed cellulose compresses over time and LOSES R-value through increased conduction as it compresses.
Properly installed (and properly performing) cellulose and fiberglass insulation are comparable in R-value and thickness.
Cellulose slows flame spread because there is less air in the cavity (because it is compressed and therefore not offering the same R-value, or resistance to heat transfer).
It is NOT, however a UL approved method of slowing flame spread, and therefore does not carry a rating such as "2-hour firewall". Underwriters Laboratories rates walls, and they DO NOT rate components. They rate assemblies. So, there is no such thing as insulation "creating a 2-hour firewall". There is a 2-hour assembly which includes insulation, among other components (like fire rated gypsum).
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