Many of my clients begin discussing things they'd like to do in a home to make it a "Greener" home. Often I hear of possibly using geo thermal heating systems, solar panels, and even wind to power their homes. Once price is discussed these items often get pushed back on the wish lists either due to the cost or the fear of appraisals not being able to be achieved. Appraisers need to form an opinion of the property by the homes around it. If it is the same home as the neighbors, but has a $40,000 geo-thermal heating system in it they feel most buyers are not willing to pay that difference. Therefore the appraisal will come in less than needed to complete the project and the difference needs to be covered in the form of cash by the homeowner. At this point, I typically discuss spray foam to allow them to enhance the homes efficiency and do so without spending an excess of money. Often, I can spray foam a homes sidewalls for $3000 to $5000 more than a typical fiberglass insulated home. This is a workable number for appraisals and one that can typically be included in the price of the home without outlaying additional cash from the homeowner. The biggest difference in the way spray foam acts vs typical fiberglass insulation is the removal of air movement between the interior and exterior of the homes wall which I will call the stud pocket. I tell people that there are 3 ways heat is gained or lost. It happens through conduction, convection, and radiation. Radiation typically occurs through the windows of a home, while conduction occurs through the pass through of walls. The best way to describe conductions path of heat transfer is when you put a metal rod in the fire. You will burn your hand if you hold on to the end that is not in the fire eventually. The last way is convection. With spray foam insulation, convection has a difficult time occurring because we fill the entire stud pocket with the foam. Often people can feel air movement in the outlets of homes built in the past. This is typically not the air directly from the outside, yet the air spinning in the stud pocket behind the sheetrock. In the winter, the homes internal wall temp is around 70 degrees so the air in the stud pocket starts to rise. As it gets to the top, the air hits the outside wall where the temp can be minus 10 degrees so it begins to drop. The more dramatic the temperature difference between the two surfaces, the faster the air spins in the wall. This is why a typical fiberglass insulated wall actually loses R-value as the temperature difference increases. A home with an R-value of R-19 is based on the fact there is only a 10 degree temperature difference between the inside of the home and the outside. This is where closed cell spray foam shines. If we fill that entire stud pocket with something that does not allow any air movement, we eliminate one of the three ways heat can be transferred in the home. R-values on spray foam homes stay very stable despite the temperature changes. It does 2 other great things as well. It strengthens the outside walls and it makes for a much quieter home in the inside. I have talked in depth about the Energy Star ratings on homes and the one thing I'd like to mention is that our homes Energy Star ratings don't differ that much when we use one type of insulation or the other. We are still able to build an extremely tight home with fiberglass insulation. The true benefit comes through the energy bills my clients receive, although I don't have a true idea on the payback that each home will receive. If I spend $5000 extra to put spray foam in and it performs like I've mentioned above, the payback is much easier to achieve than a $40,000 Geo-Thermal heating system. I hope this helps you better understand the homes possible insulation systems.