People usually select insulation by its “R-Value”. This term indicates the amount of Resistance to heat and cold transferred through a material. The higher the number, the better. A typical Wisconsin home meeting state energy codes would have an R-19 in the exterior walls and an R-38 in the attic. Here, as in the rest of the U.S., most homes are insulated only enough to meet the minimum code requirements.
But no matter how much R-value a wall or ceiling has, if air leaks through, the home can be drafty and energy bills will be higher. Sustainable builders and designers know that an equally important factor is how well the home is sealed, and this is done through selection of insulation that has both a high R-value and tight sealing capability.
In this article, we’ll review various types on insulation. Next time we’ll discuss where and how best to use it.
Insulation comes in four basic categories. From lowest R-value to highest, they are: batt, blown, sprayed, and rigid.
Batt insulation, usually made from fiberglass, can provide the minimum R-value required by code. It is inexpensive and easy to install, so it is most commonly used insulation in standard construction. It does not protect adequately against air leakage.
In sustainable construction, insulation is more often blown in, sprayed in, or applied in sheets, as these methods provide a tighter, better thermal barrier.
The most widely used blown-in insulation is cellulose, made from recycled paper. Dry cellulose is blown tightly into wall cavities and loosely into attics. It may settle and compact, which diminishes the R-value. It may require replenishing over time, especially in attics. It can also produce dust particles which aggravate respiratory problems. But it is considered to be a good, affordable, “green” option for insulating and sealing walls, and for insulating attics.
Virge Temme
Sprayed foam insulation generally provides the tightest seal, and comes in two varieties: closed-cell and open-cell. Both are used in walls and attics. Closed cell, like polyurethane or polystyrene, is heavier, denser, and will lose a percentage of its initial R-value within the first year. It can become hard over time and crack as a building shifts, compromising it seal.
Open-cell foam insulation is made from soy or icynene, an inert water-based product. Its two greatest attributes are pliability and R-value retention. The pliability of open-cell foam insulation allows it to adhere to framing materials and move as the walls expand and contract, creating a very tight seal. While you may spend twice as much on soy foam or icynene as you would on fiberglass batts, these foams have a remarkably short payback period. Open-cell foam insulation is favored by Energy Star and LEED experts because of its success in reducing heating and cooling costs.
Rigid foam insulation (Expanded or Extruded Polystyrene) is most often used around foundations or under concrete slabs. Because it has a very high R-value per inch, it is sometimes installed in combination with batt insulation to improve overall R-value of the wall and provide a better seal. It is also used in SIPS (Structural Insulated Panel System) and ICF (Insulated Concrete Forms) which will be described in a future chapter.
The best insulation, though, is only as good as its application. Please tune in next time to learn how to make certain your home is at its draft-dodging best.