Building Envelope Insulation

When discussing home insulation, one of the first items to discuss is R-value. R-value measures the heat transfer through a given material and gives you an objective for the results of your insulation. Homes in Texas are generally designed to maintain between 20 to 30 degrees differential between outside air temperature and indoor air temperature, and are designed to be more efficient in the summer than in the winter.

Cellulose insulation (essentially recycled newspaper product) is permeated with boran/borax or some other kind of insecticide in an attempt to keep it from becoming a food source for insects as well as fire-retardant chemicals. This newspaper cellulose product compacts over time as it breaks down leaving void in the spaces it originally filled. As the cellulose paper based material eventually breaks down over time the dust that remains will include the insecticide and possibly find its way into the home. This is 1 reason the use of cellulose insulation has been on the decline.

The most traditional and widely used form of home insulation in Texas is fiberglass batts. While fiberglass causes some itching it’s been around long enough to have a very well established track record of what it will and won’t do. Batts go in the walls of the home and floor of the attic in the home. Fiberglass batts come in various thicknesses (R values-the higher the number the more resistive the material is to heat transfer). A new trend in fiberglass batts is paperless batts. The concept is eliminate the paper and eliminate a potential food source for bugs and mold.

Another widely used and extremely effective wall and attic insulation method is blown fiberglass. This has the advantage of the cellulose installation - being able to get in all the tough spots and a relatively simple installation process. It is used in both new home construction and remodel applications. It’s very effective at creating high R-value insulation but can be messy and over time can become packed down or removed entirely.

Spray Foam

There are 2 types of spray foam insulation: open cell and closed cell. Many open cell spray foams are made from organic materials such as soybean oil and use water or carbon dioxide as the blowing agent.

The blowing agents in most types of closed cell spray foams are hydrofluorocarbons (HFCs) with a high global warming potential. Many green builders avoid the use of closed-cell foam for this reason.
Applying Foam Insulation
Spray foams are an alternative to blown or batt insulation. Instead of going in the walls of the home and floor of the attic, it is sprayed into the walls of the home and the rafters/ceiling of the attic. The concept is to completely seal the house with a very high R-value material. The result is a much cooler attic.

Spray foam insulation has been becoming increasingly more popular but more expensive insulation option. As the installations age over time we will be able to determine if it really is a better way to insulate in Texas.

Radiant Barrier
If you are using fiberglass blown or batts in your walls and floor of the attic you definitely need to install a radiant barrier on the inside of the roof deck. Roof decking now has a radiant barrier pre-applied so there’s no additional labor costs during new construction. In a retrofit environment there are metallic paints that are as effective as their installation procedures. A radiant barrier requires an airgap (about 6”) between the radiant barrier material and portion of the house seeking to be insulated.

Because the radiant barrier needs an air gap to be effective, radiant barriers are not used on the inside of the attic in spray foam installations.

Crawl Space
Crawl spaces should be designed to allow excessive levels of water that may enter a home's lot to flow through the space. Crawl spaces should be properly insulated.