Rigid insulation is a form of insulation that is often overlooked. Fiberglass is the most popular insulation by far, but let's take a look at how rigid rates on the scale of insulation, and how it compares to other types of insulation, including the all too popular fiberglass as well as cellulose and mineral wool. Some differences are minimal, and some are very big. However, until you understand the differences between a rigid insulation and a cellulose one, how can you choose which is right for your home or project?

The first thing to consider with insulation of any type is the R value; the R value is an indicator of how good the insulation is this basically tells you how efficient the insulation is, and what temperatures it can withstand etc. If you do not know what the minimum R value standard is for your climate or area it would be wise to find out, otherwise, you can never really go wrong by getting the highest R value you can, although it is not always necessary and can be an unneeded expense. For rigid insulation the R-value is 4.0 to 6.5 per inch. The R value for fiberglass and cellulose is 3.2 per inch, and for mineral wool, 3.1 per inch.

So, as you can see, rigid insulation varies in value, but has a higher R value than most other types of insulation. Let's take a more in depth look at rigid insulation, and some of its benefits. First, let's look at what it is made from: there are various types of rigid board insulation, made from various materials such as polystyrene, polyisocyanurate, compressed mineral wool and rigid fiberglass.

Rigid insulation is used in a variety of applications both above and below ground. It offers the great benefit over insulation like fiberglass in that it is waterproof or water resistant. And it compares with cellulose and fiberglass in that it is available in a variety of sizes and thickness.

So, when do you use rigid insulation over another type? Well, rigid insulation is often used on exterior and below grade foundations, under basement slabs, as a backer for vinyl siding and as an insulator for basement walls. These areas require insulation that has a high R value and that can withstand moisture and water as the basement is more likely to receive a lot of water than say the second floor.

Rigid insulation is not just for the foundation though, it often used to supplement the insulation in walls and ceilings. It is a great alternative to some of the other insulations as adding a half inch of polystyrene foam board installed beneath the wallboard can give the equivalent of 5 1/2" of fiberglass in a 3 1/2" thick standard stud wall.
An additional benefit of rigid insulation is that it stops the conduction of heat from the outside through the wall framing. This gives the result of eliminating "cold spots" on the wallboard at each stud.

Well, with all of its benefits there are some drawbacks as well; one problem with rigid insulation is insect infestation. While it is the best insulation as far as heat and cooling and conductivity goes, it attracts insects, especially carpenter ants. In warmer climates, pest control professionals suggest that you not use below-grade foam insulation at all unless the foam stops well beneath the surface of the ground to allow for termite control. It seems that termites have found rigid insulation an ideal medium for tunneling, and use it to reach above grade wood. So, if you live in these climates, avoid rigid insulation, or properly exterminate and use pest control regularly.