There are many different ways of building an energy efficient home. While traditional construction can be made more energy efficient than in the past, alternative and panelized materials often yield high R-values as well as a much faster construction time, and often a lower price tag. When considering insulation it is important to consider walls, ceilings and windows. The floor may also be of concern, depending on the landscaping and floor height from the ground. It is especially important to insulate a second story floor over a garage. Insulation under a low crawl space is less important, if the crawl space is well enclosed. The same insulating materials can be used for walls, floor, ceiling and roof in most cases, with the emphasis being on walls and roof.
Building Energy Efficient Home: Traditional Stick Construction
In order to get enough insulation in the walls, it is best to use 2 by 6 inch studs instead of 2 by 4 inch studs. This adds to the strength of construction as well as providing ample room for insulation. Closed cell insulating foam yields an R-value of 6 per inch, so with 4 inch studs ( which really aren’t 4 inches anymore, you’d have an R- value of 18, but with 6 inch studs you’d have an R value of 30.
Composite Technologies Corporation has a patented system which yields an R-value of 29. This amazing wall is constructed of a 2 inch thick layer of concrete, and a six inch layer of concrete, with a core of 2 three inch layers of polystyrene, all bonded together. These powerful walls are 14 inches thick and should withstand just about anything life throws at them.
Some Insulated Concrete panels have only 2 inches of foam core and three inches of concrete on each side. The R-value of these types of panels can be disappointing, only yielding about a 5 R value on a hotbox test. Solarcrete ICPs have yielded R-values of up to 36. The walls are 12 inches thick, with over seven inches of expanded polystyrene foam in the center. The important variable is clear. It isn’t the concrete that insulates, it is the foam, while the concrete provides a strong structure. Therefore a 6 or 7 inch insulating core is needed to yield those fabulous R-values, while strong concrete makes the home durable. Of durable materials, concrete panels and other Ferro-cement techniques rank very high.
OSB Insulated Panels – A thick layer of polystyrene or polyurethane foam sandwiched between to layers of 7/16ths OSB plywood, is designed to replace structural framing, insulation and exterior sheathing. Some SIPs contain 3.5 inch foam core, and some have a 5.5 inch core. In hotbox tests the panels with a 3.5 inch core yield R-Values around 15, while the 5.5 inch panels yielded the incredible R Value of 23.Any exterior and interior finishing materials on both sides of the wall will add to the R-factor.
Wood is a good insulator. A seven inch thick, tongue and grove wooden wall will give you an R- value of around 10. Log panels are extremely cheap, but the logs are no thicker than clapboard siding (3/4 inch). They have a backing of plywood and then studs. When properly insulated within the studs though, they have great potential for energy efficiency. The biggest plus for these is that they yield a shell home for $21 per square foot, and can be built on site in a day.
4 inch stud wall – R value 19 (3 inches of closed cell foam)
6 inch stud wall – R value 31 (5 inches of closed cell foam)
4 inch SIP – R value 15 (3 inches of foam)
6 inch SIP – R value 23 (5 inches of foam)
14 inch ICP – R value 29 (6 inches of polyurethane)
12 inch ICP – R value 36 (7 inches of foam)
8 inch ICP – R value 5 (2 inches of foam)
7 inch log – R value 10 (no foam)
Log panel – R value 15 (fiberglass insulation)
Log panel – R value 19 (3 inches of closed cell foam between studs)
As you can easily see, the more polystyrene, polyurethane or closed cell spray insulation you use the better the R-value. No matter what your building style of choice, the new insulations are leading the way in building an energy efficient home.