What about spray foam insulation?
There are many types of insulation in the market today. Which is the best, there are many things to consider. Following is a discussion of Spray Foam insulation & issues to evaluate when considering foam as your choice of insulation. There are two main types, open and closed cell. Each has pro and cons.
- R value
What do the terms “Open Cell” and “Closed Cell” mean?
When foam is installed in a home or other structure a cellular plastic is being made on site. For simplicity, think of it as bubbles in a bubble bath. The insulation cures very quickly and of course is dry once cured, unlike the bubbles in a bubble bath. Foam is a combination of 2 chemicals, an activator and a plastic. In simple terms the rate at which these are mixed can determine the foam structure.
In open cell foam, a majority of the millions of bubbles share walls with one another, thus making it soft and airy. Only a few percent of the finished product is plastic and the rest is mostly carbon dioxide trapped within the structure. These foams typically are light and only weigh .5 – .6 pounds per cubic foot. The general definition in the industry for open cell foam is that greater than 50% of the cells are open. Open cell in general has less plastic, in soft to touch, has no structural value, has an average r value of 3.5 and is significantly cheaper than closed cell.
Closed cell foam forms in a similar manner. However, a majority of the cells in closed cell foam are independent from other cells in that they have their own cell structure and do not share any of their structure with other cells. The resulting foam has a much higher plastic content and less air/gas content. The foam is strong, rigid, and typically weighs 1.7 – 2.0 pound per cubic foot. The general definition in the industry for closed cell foam is that greater than 90% of the cells are closed. Closed cell in general has a higher amount of plastic, is more ridged and has a structural component to it, is more costly but has approximately twice the r value at 6.5
What does “R Value” mean?
R value is the measure of thermal resistance. In general the higher the R value the better the resistance to heat transfer. With respect to foam products, they maintain some of the highest values per inch of use. The chart below details some of the general values for differ types of insulation. The value each type is rated at is under ideal circumstance in a laboratory. In the field these conditions can change dramatically and have a disastrous effect on the performance of the insulation. Conventional fiberglass batts often are jammed into locations too tightly or are not installed correctly around fixtures and penetrations, ie an outlet on an exterior wall. This lowers the overall effective R value to the insulation and allows drafts to develop. Additionally it is noted in the journals and codes, that insulation to be effective it must be direct contact with framing on all 6 sides to approach the listed r value (this is greatly affected by air sealing discussed later).
Often applicators spray open or closed due to the differences in style of application. One can be more complicated than the other. But no one foam is best in all instances. Closed cell while provides and affective air and moisture barrier at about 2 inches gives you about an R13. This can be acceptable in basements but not in roofs. Because of the
closed nature if you use closed cell in the attic on your roof, you will not see a leak until the roof fails. Plus with closed cell it can make an echo chamber effect and be loud. Closed cell foam can be sprayed in a maximum of 2-3 inches at a time because of the heat buildup of the chemicals being used. So in aiming for a higher R value you need to make multiple applications allowing foam to cool between coats. This adds time and cost to the installation.
Open cell on the other hand if applied to a roof will let the water penetrate so a problem can be seen before it becomes a structural issue. Secondarily it also makes for a quiet room because of the open cell nature it absorbs sound. It’s R value is about 3.5, less than closed but because of the chemical components it develops less heat in application and can be sprayed on in thick layers without concern of heat buildup.
Lastly, most insulation is very dependent on air sealing. Air sealing is the action of sealing all small cracks, crevices and penetrations. There is no other product on the market that air seals & insulates in one application, other than foam, open or closed. This is why foams in general get higher R values than fiberglass, cellulose or denim.
Foam is an outstanding product, but you need to know when to use each type of foam. Each is unique and has benefits. In general, foam outperforms most other insulation and can often save the homeowner 20%-30% on heating bills. Hopefully with this knowledge the consumer can be better informed when considering insulating the attic or basement.