There has been a lot of hoop-la and craziness around passive homes, net zero energy homes, and super energy efficient homes. I’ve been amazed at how easy it can actually be. My friend is building a house that will burn less then a cord of wood per winter. His building cost? Around $100 to $110 per square foot. Yes, he did do a lot of the work himself. However, if a contractor would do it, the price would still be on par with normal construction.
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Before we talk about building a super insulated home, first you need to understand how to design a super efficient shell. The below 26 minute free video lesson is from Marc Rosenbaum’s 10 week, “Zero Net Energy Design” class, where students learn how to design a zero net energy home in 10 weeks.
Here’s how he did it.
1 – Keep the house small. Less resources, cheaper, and less energy use. At 1600 square feet the house will use about a half of cord of wood be winter. We’re burning mainly maple which is 20 million BTUs per cord. Thus, he’ll burn 10 million BTUs per winter. This averages around 55,000 BTUs per day. Don’t believe me, this house will use the tiniest wood stove he could find.
2 – South facing home with lots of windows. The house is facing directly south and there are only 4 windows that are not facing south. This is a view of the house at 7:00 AM on November 1st. The sun is hitting the it directly.
3 – Double Framed Walls. All the stud walls are sitting on a 12 inch top and bottom plate with 2 by 4 framed studs on the interior and exterior of the plate. This does a few things.
- A – Huge cavity for blown in cellulose. Cellulose has an approximate R value 3.8 per inch. 11.5 inch cavity thus equals R 45 exterior walls. The rafts are 2 by 12 framed with 2 by 4 strapping across the interior plane equals a 13 inches ceiling cavity.
- B – Air Barrier. Cellulose acts as an air barrier between the interior and exterior and reduces a significant amount of infiltration.
- C – Vapor Varrier. Cellulose also acts as a vapor barrier, key for controlling mold.
- D – No Thermal Bridge. Except for the top and bottom plates and framing around the windows and doors, there is no place for heat to move via conduction from outside to inside.
4. Extra Diligence of filling all holes and gaps from the interior and exterior. A few large gaps are between windows and doors that you should fill with low expansion foam. Make sure to keep in eye and follow up on your subs that might be be thinking about insolation as much as you are.
If you’re building a new home and do nothing more then face the home south, put many windows on the south face, and build it will a double insulated wall the energy usage of the home will be significantly less the traditional 2 by 6 framed homes.