I just started blowing cellulose insulation into my attic. I started, but didn’t finish, because I used a vastly different amount of insulation than was called for on the label, and I don’t know what I did wrong.
I have a bit of blown-in insulation already – about 3 inches. I decided to add an additional R-30. The area I’m insulating is about 1600 sq. ft. (I feel pretty confident of that measurement). According to the label on the insulation, I needed to add 9.3 inches of insulation, and the coverage should be about 21.7 sq. ft. per bag. Doing the math, I came up with about 74 bags. I bought 81, which I thought would give me a bit of a cushion.
Before I started installing the insulation, I built dams of fiberglass batts where the house meets the garage so I wouldn’t be blowing extra insulation outside of the area I wanted to insulate. I also went around and marked every upright on my trusses so I’d know that I was blowing in to the right depth.
I finished my 81 bags and figure I’ve only insulated about 60% of the attic. I’m looking at installing almost twice the amount of insulation I originally estimated.
What could I be doing wrong that would put me so far off? I’m not sure if I did something wrong, or if the estimate on the label could be so far off.
Replies
you're probably not getting the fluff it was figured on
the way we do it is to divide the attic into sections, figure out how many bales you need to blow in each section and blow just that..... don't put any more than what you had figured
open blows in attics should be figured on 1.46 lb/ cf
figure what you need for cf to get the R-value you want
So would the areas he has done so far be considered dense pak then?when in doubt add garlic
it's an attic.. an open blow.... you can only get "dens-pak" in a confined space so you can compress the fibersMike Smith Rhode Island : Design / Build / Repair / Restore
duhwhen in doubt add garlic
What, a manufacturer that exagerates their products specs?! I've never heard of that before. :-)
It's probably due to the type of blower you used, and as Mike said it's as much material as the manufacturer claims, just not as fluffy.
Celulose settles siginificantly over time so I can't see that it makes a spit of difference in the long term.
It's hard to have too much insulation.
Beer was created so carpenters wouldn't rule the world.
Is the R value the same if the blown-in insulation is not fluffed as much as the manufacturer assumes?
So how do people who are selling their houses convince the buyers that they have a certain level of insulation?
So how do people who are selling their houses convince the buyers that they have a certain level of insulation?
You don't have to lie to anyone, just tell them that you've blown in the number of bags the manufacturer suggests for whatever R-value you're shooting for. A house inspector will quickly see how thick it is so his report will go off that number unless you have some proof that he's willing to consider that suggests a higher number.
Beer was created so carpenters wouldn't rule the world.
Is the R value the same if the blown-in insulation is not fluffed as much as the manufacturer assumes?
Yes and no. It's probably very close to the long term R-value (after settling) but not quite as high as freshly installed celulose.
Fiberglass doesn't settle, not that alone makes it a better insulation. Celulose is still the best route per $ for most instances.
Beer was created so carpenters wouldn't rule the world.