It is certainly possible from the perspective of mathematics, but we find measuring by the pound or even cubic foot can add undue confusion to a simple equation. A driver of the misunderstanding is often where the insulation sits and what densities are required as a result.
The following will ideally shed some light on a matter we are increasingly asked to address.
Measuring Regular Insulation
The easiest way to quantify your insulation requirements is to measure the square footage while noting the cavity depth – often 2x6s, which are 5.5” deep. For example, a room that is 10’ x 20’ requires more than 200 s/f of insulation. Assuming 8 foot walls and no windows, for purposes of the exercise, you will have 4 walls, 2 are 80 s/f each (8*10) and 2 are 160 s/f each (8*20), that require a total 500 s/f of insulation. If there is a window or a door, measure their dimensions, assume the square footage, and subtract it from the total. Also, it is a fair to say the 1.5” occupied by each stud can be added and then also subtracted from the total. Most of our clients avoid this step so any mismeasurements might be made up with the slight overage caused by not netting out the studs.
The floor and ceiling can be added using the dimensions of the room – 200 s/f (10×20′). The cavity will probably be larger eg 2×10 or 2×12 thus requiring more depth in insulation. Attics and roofs can add challenges with knee walls, and pitch angles but your GC can help, or you can call us and we will!
Measuring Insulating Wool
If you are using Havelock Wool insulating wool, you can use an R19 batt or 5.5” of loose-fill to achieve R24 in the 2×6 cavity. Often times we see clients use loose-fill in exterior walls and batts in interior ones.
A per cubic foot calculation can easily be achieved by noting that our loose-fill should be applied at a density of 1.13 lbs per cubic feet. In a 25lb bag one can then cover 22.12 cubic ft. Again, the math is fairly straight forward so this method is certainly feasible; however, we do see it lead to confusion and often times extra material is purchased. Also worth noting is that densities required can very greatly amongst insulation mediums. For example, our proprietary manufacturing process allows for Havelock Wool loose-fill insulation to exist at the same density whether it is in a wall (vertical) or an attic (horizontal). By comparison, chopped wool may slump; cellulose may require up to 3.5-4lbs per cubic foot when applied in a wall cavity.
There is little need for this blurb to become overly technical but please note not all insulating wool or otherwise, is created equal and we hope to shed a bit of light on the equation. For more information, contact us below.