Not all insulation is created equal
Most everyone is familiar with the pink, yellow or white fiberglass insulation found in many, many homes. People know the strutting pink feline character that shows us how this stuff will keep our homes warm and our energy bills reasonable. If only he had an infrared camera, the things he’d see!
There has been controversy surrounding the effectiveness of fiberglass insulation for years. Mostly between the manufactures and building science experts. The facts are strong that fiberglass is poor insulation that rarely performs as stated.
In the first infrared image (Figure 1) which was taken in the summer, this insulated ceiling doesn’t look to be completely insulated. The hot attic air is moving around the insulation, or more accurately the vapor retarder, rendering it less effective. Air also easily passes through fiberglass (they make filters out of this stuff). Exposed fiberglass attic insulation is subject to convective loops and studies have shown its performance diminishes dramatically as temperature difference increases (winter or summer).
The second infrared image (figure 2) shows a section of attic floor (or the ceiling below in the living space) where heat is bleeding through about 8 – 10 inches of blown in fiberglass. That is not old or damaged insulation. This house is just a few years old! Loose or blown fiberglass is a far worse insulator than its cousin, the batt. The R value per inch is significantly lower, about 2.2 as compared to about 3.7. What’s even more disturbing is this marginal insulation gets blown inside walls. Fiberglass works by air pockets in the material trapping air. If you compress it, no matter the form, the insulating value is diminished.
Cellulose insulation (figure 3) on the other hand is not prone to thermal or convective problems. First cellulose does not require a paper or plastic vapor retarder. The material is hygroscopic, meaning it manages moisture quite well. Cellulose can be sprayed or dense packed into wall and ceiling cavities leaving no voids around mechanical penetrations. Cutting and fitting batt fiberglass insulation around electrical boxes, plumbing and heating fixtures results in voids that create airways. With cellulose compacting the material increases the R value, unlike fiberglass. Cellulose also has a slightly higher R value (3.8 / inch) than high density fiberglass (3.7 / inch). Probably best of all it is made from recycled materials (paper) and uses significantly less energy (750 Btu / lb.) to manufacture than fiberglass (12,000 Btu / lb.) or foam insulation (33,000 – 48,000 Btu / lb.).
While cellulose does seal and prevent air movement far better than fiberglass products or any insulation type in batt form, sealing all bypasses is essential to the maximum performance of any insulation. If new insulation is installed without closing off the bypasses, the full effectiveness of the new insulation will not be realized.
One potential problem with cellulose, particularly in retrofit applications, can be seen in the final infrared image (Figure 4). Some of the wall cavities were incompletely filled by the installer. Older cellulose was known in some instances to settle, which is attributable typically to a poor installation. Cellulose today is manufactured to eliminate settling by making the material somewhat “springy”. Further by dense packing it in the wall cavity the material is under slight pressure and can not move. No more settling problems.
The benefits of cellulose fiber over other insulation, most notably fiberglass, are considerable. Too often what decides which insulating material will be used is initial cost. While cellulose falls somewhat behind behind fiberglass, about one and a half to two times the price of fiberglass, it more than makes up for in performance with higher energy savings over the life of the structure. This savings will more than offset the extra up front cost.
Continually seeing air leakage and poor performance through the infrared camera lens has made it apparent to me that using fiberglass insulation is a bad building practice. In the long run using superior performing insulation products such as cellulose will help make our homes more comfortable and energy efficient.