Midcoast Green

Midcoast Green Collaborative > Home > Articles > Batts & Loose fill

Other Batts and Loose Fill Insulation

by: Paul Kando

In my last column I emphasized that, after structural integrity, insulation is perhaps the most important feature of a comfortable house. Since insulation is relatively inexpensive and easy to install during construction - and more difficult to add later - there is simply no rational excuse for building a poorly insulated structure. Over time, well-installed insulation is the best investment one can make. My earlier column considered Fiberglass batts, by far the most popular insulation used in residential construction. However those batts must be installed with precision or the building will not perform as expected. When compressed, fiberglass loses some of its R value and tests have shown that a 4% void (a mere half inch gap on top of a wall stud bay) can reduce efficiency by as much as 50 percent. Installing batt insulation calls for attention to detail many installers don't bother to give it.

Fig. 1 Filling wall cavities with cellulose insulation.
photo credit:

Alternatives to fiberglass batts include batts made of other fibrous materials, loose fill, or blown-in insulation, and insulating foams. Batts are made of mineral wool, or rock-wool as well as cotton and even wool. Rock wool, produced from certain kinds of rock or blast-furnace slag, is more dense than fiberglass and has an R value of 4.2 per inch thickness, higher than fiberglass (R 2.9 to 3.8). Rock wool is highly resistant to fire and loses no insulation value when it gets wet. Alas in the U.S. rock wool batt insulation is fairly hard to find for residential applications. It is made in thicknesses up to 6" in standard 16" and 24" widths, faced and unfaced.

Cotton insulation batts have been primarily niche products, but are gaining in pupularity. A popular variety is made of mostly post-industrial denim waste and, not surprisingly, comes in the color of blue jeans. Cotton batts, unlike fiberglass, are made without chemical binders and are recyclable. On the other hand, they come only unfaced and in fewer thicknesses than fiberglass. The cotton batts are designed to be friction-fit into 2x4 and 2x6 walls (R-13 and R-21, respectively) and are much more difficult to cut to odd sizes than fiberglass.

Woolen insulation batts conjure up a cozy image of a home wearing a bulky woolen sweater. They come treated against mold, rodents and insects but contain no chemical irritants. Wool insulation is fire resistant, self-extinguishing, bio-degradable and hygroscopic, i.e.: it can absorb a fair amount of moisture then dry out without damage. In the U.S. wool insulation is rare. It is also relatively expensive. I don't consider it a practical alternative.

Loose fill insulation has been around in various incarnations since at least the 1950s. Vermiculite and rock wool came first. Blown-in fiberglass followed, especially in attics where it was easy to apply. Cellulose, the modern choice, is made from recycled newsprint and treated to make it fire-resistant. The preferred treatment is with borates. (However, before borates came into use, cellulose insulation was treated with ammonium sulfate. Avoid any insulation still treated this way: with the slightest wetness it gives out a foul odor that can linger on after the insulation has dried).

Loose-fill insulation is ideal for attics where it can be applied in a thick, uniform layer. In existing wall and ceiling cavities it can be blown it through holes drilled for the purpose. In new construction the fibers are mixed with a binder at the nozzle of the blowing machine, This forms a matrix that reduces air flow and helps the mixture adhere to the sides of the cavity being insulated. Properly applied, blown insulation is a better way to insulate than batts of any kind: it flows around pipes, wires and obstructions and, by minimizing air flow, it helps prevent both air infiltration and moisture problems inside the building structure.

Neither loose-fill fiberglass nor cellulose contain a formaldehyde binder (something to avoid with fiberglass batts). While it costs about the same as loose-fill fiberglass, cellulose has a higher R value &emdash; R-3.7 vs. R-2.8 per inch of thickness. Cellulose also qualifies as "green"; it improves energy efficiency, it is not toxic, it has a high recycled content and it is recyclable.