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# calculating blow in quantity

#1
02-06-11, 07:11 PM
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Join Date: Oct 2008
Location: South Dakota
Posts: 327
calculating blow in quantity

I have measured my attic spaces, and need some assistance in determining how much blow in that I will need. My first question, is that I have multiple side attics in my home. In order to determine the square footage of these, it would be the length times width, divided by 2, correct? Secondly, once I do have the total area of attics determined, how does a person determine what a bag of material will cover?? I understand that the bags apparently say on them how many square feet they will cover at which r-value, but is there any generic rule of thumb to these?? I am currently trying to compare cellulose to fiberglass, in respect to how much of each type of material it will take to do the job, and weighing out the cost difference. Thanks .

#2
02-07-11, 05:33 AM
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Join Date: Feb 2006
Location: USA
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Area

square footage of these, it would be the length times width
This will give the area in square feet.

divided by 2
This will give the cubic feet for coverage 6 inches deep.

#3
02-10-11, 08:14 AM
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Join Date: Oct 2008
Location: South Dakota
Posts: 327
the ones in which I divided the square footage by 2, are for the side attics. For side attics, since they are a triangle, they would be only half the area, correct?...

#4
02-10-11, 11:27 AM
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Join Date: Oct 2008
Location: New England
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If you assume your sq footage is one foot deep, then it is the volume in cubic feet. Divide by 2 gives you the 6" of depth. So, 1,000 sq ft area at 12" deep would require 1,000 cubic feet of insulation. If you only want to add 6" of insulation, divide by 2 and you would need 500 cubic ft.

The bags of insulation will tell you how many cubic feet they provide and generally will show the area at different depths. Length times width is area of a rectangle, which should be your floor area. Just add all of the side areas and others for your total.

Bud

#5
02-10-11, 02:51 PM
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Join Date: Feb 2006
Location: USA
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Triangles

For side attics, since they are a triangle, they would be only half the area, correct?...
The area of a triangle is base times height divided by 2.

Are we talking the area above the main floor ceiling? Blown in on top of the ceiling? Are you sure about the triangle shape?

#6
02-10-11, 05:42 PM
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Join Date: Oct 2008
Location: South Dakota
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I am referring to the area within the side attic. I am questioning this, since, in a side attic, there is the knee wall, and on the other side, the roof slopes down, to meet the eave. At the end where the roof slopes down. But, it would make sense that these would simply be figured by floor dimensions, since the insulation is blown on the floor...

#7
02-15-11, 07:56 AM
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Join Date: Oct 2004
Location: PA
Posts: 2,210
Step One - Calculate Your Need | GreenFiber.com

I used that chart and came out pretty close. I had many different existing R values in the attic then one section where there was a floor that was a big challenge to figure out. I bought 60 bags and actually needed more for under the floor but thats what spring is for!

the calculator was pretty accurate though, i brought up to near an R60 and just subtracted out the existing R value from the depth in the chart. do yourself a favor and put a lot of rulers or other marks all over the attic, i had marked my vertical joists but even that wasnt enough..but heck i'd rather over than under insulate...buy a 500 watt light and a very good vented dust mask.. you must use it. i looked like i walked out of a volcano after i was done. Also put a large tarp under the machine, we gathered about a bag full of 'waste' from the ground and used it.

enjoy your savings! my kitchen immediately was warmer after going from 2 inches of degraded loose fill to that R60.