Attic insulation coverage issues

[2011laramie]

So this is my 3rd time doing blown in attic insulation, first time was just a top up, 2nd time was small garage in town, no real organization to the madness, but didnt get coverage and had to buy more bags to finish end of garage.

This time I carefully run string lines in attic to ensure proper depth and accuracy of bag coverage based on chart on back of bag. R50 cellulose should be installed 15.15". So i string it out at a smidge above 15". We got 107 bags to do, each bag should cover 13.3ft2. Do all 107 bags and definitely around 250ft2 short.

I dont feel like im excessively packing the insulation, its nice and fluffy and very level with strings. Ive still got a bunch more to do when more cellulose shows up to the store.

What am I doing wrong to not get the coverage? I was targeting R50, but at the current rate of bags/ft2 itll be closer to R60.

 

[yatg]

How many square feet of attic floor are you actually trying to cover?

What's the brand and bag size of your insulation?

based on your numbers,
13.3 sqft/bag * 107 bags = 1423 sqft of attic floor

 

[2011laramie]

Shop is 2816 total. I bought 215, 107 were delivered, i figured it get roughly half of the roof done. But like i said i came up about 250ft short, so then i ordered 40 more just to be safe. Now im just waiting on delivery whenever that happens.

 

[CombatNinja]

Blown-in cellulose is like paint or stain coverage. I use what it says on the label as a guideline but figure that +/- 10% is perfectly acceptable. You are a little above that but a million things can effect coverage rates, from the blower you are using to the technique of the person loading it and the technique of the guy at the business end of the hose. Don't sweat it and just finish it out. If you end up anywhere between R50 and R60 with no air leaks, you are good to go.

 

[mv213]

It also varies depending on the machine. If you are using the rental/loaner machines like from Home Depot or Lowes, those fluff up the insulation the least, reducing coverage. A large professional machine does a much better job of fluffing up the material. However, I don’t know if that affects the R-value or not.

 

[CombatNinja]

How much it is fluffed up definitely changes the R-value. It, like any insulation, works by trapping air. Less fluffy = less air = lower R . It is common in older homes from the 1980s that were built with R-30 blown-in having had the insulation settle or all get disturbed over the years to the point where it has lost half the R-value.

 

[rburke65]

Did you used the same ai4 pressure that “they” used a the lab? Why too m@ny variables. Leave it as is or buy more bags. Same with paint coverage....or sealing asphalt, or grass seed. Always buy more.