Step # 4 In our current series of articles, we are chronicling the steps to construct an energy efficient home based on a current project here in Flagstaff. We are building a house for a professor just north of NAU who is prioritizing energy efficiency. The first articles covered the basics of getting out of the ground. The next few topics will dive deeper into the details.
Now that we are vertical, we need to address getting the house tight and insulating it properly. By now, we have decided on a stick built house with “advanced framing” techniques and cavity filled wall insulation and spray foam “conditioned attic” insulation. This is a concert of techniques and materials that we chose for the balance of cost versus performance; however, there are a few other wall and roof systems that you might want to look into. One such system is called SIP construction. SIP stands for Structural Insulated Panel. SIPs are basically two sheets of plywood with a foam core inside. They go up in large sheets and act as the structure and the insulation. One huge advantage is that there are no solid wood studs to thermally bridge the cold through the wall. Another is the speed of construction when using the large panels. One of the disadvantages is the high cost. Whatever method you decide on, you will need to make sure the entire structure is insulated and sealed up tight.
In our house, we elected to use advanced framing and fill the wall cavities with cellulose insulation and then use spray foam on the floors over the garage, crawlspace and in the attic. We lose a lot of heat energy out the floor and roof, and not as much out of the surface of the walls, so spending more on the spray foam in the lids will pay off quickly. One of the many advantages to using spray foam is that it sticks to horizontal surfaces and won’t fall out, and at the same time it provides an air seal for those surfaces. Pretty much as a rule, we now use spray foam for all roof insulation. When you put the insulation on the roof sheeting instead of on the ceiling, it is called a “conditioned attic” space. This makes it easier to guarantee that the lid is sealed effectively, and you won’t have the temperature fluctuations that happen in a typical attic that often lead to water condensation, mildew and ice damming.
When we build our houses, twice during the construction we make sure all the cracks are filled and sealed. The first is right after the roof is insulated. Our first pass uses standard caulking and small cans of foam to seal all the studs to each other, all top plates and bottom plates to each other and to the sheeting, and all pipe and wire penetrations. Then, using a blower door to depressurize the house, we locate any problem areas that we may have missed and make sure they are air tight before applying the drywall. The second pass will be after the house is done, when we make sure that all the drywall is sealed to the floor, all mechanical dampers are working, and all weather-stripping is tight and working properly.
It is important to remember that when you make a house super tight, you need to address having adequate ventilation. We will discus that and the other mechanical systems in the house next time. You can follow the progress of the home on our blog at: http://hopeconstructionaz.blogspot.com/. FBN
David Carpenter is the owner of Hope Construction, a general contracting and construction management firm with an emphasis on sustainable building. He can be reached at 928-527-3159.