Brad and Linda selected level three—the “greenest” option, which is closer to Passive House standards or for clients who are contemplating a net-zero annual energy use home. This design uses an insulated nonbearing stud wall constructed with 2 by 4s along with an 8.25-inch SIP, resulting in a 12-inch-thick wall. Separated from and on the interior side of a SIP, this construction method eliminates almost all thermal bridging. The space created by the inner wall provided easy access for plumbing and wiring runs. After the mechanicals were installed, it was packed with cellulose insulation. We used a 12-inch SIP roof and placed the structure on an insulated slab with R-20 around and under the slab, which was double the code requirement.
When building with R-48 walls, it is always disappointing to install R-2 or even R-3 windows, since that draws down the envelope’s overall thermal performance. Brad and Linda specified Andersen E-Series/Eagle double-hung, double-pane, low-e windows with R-values ranging from 3.33 to 3.7. We “tuned” the windows for passive solar gain, specifying a higher solar heat gain coefficient (SHGC = 0.39 to 0.44) for the south-facing glazing.
It is great when clients come to the table knowing they want to use the sun to help maintain the thermal comfort of their home. We often have clients who say they want to design a passive solar home, but then prioritize orienting the home for the view rather than solar access. For this project, Brad and Linda had actively sought out a property that was in alignment with their solar goals.
It is fairly easy to get sunlight and solar gain into a building; the challenge is to keep it in the building once the sun sets. This is where the structure’s insulation and thermal mass (in this home’s case, a concrete slab floor) come into play. Another vital element of a passive solar structure is involving the occupants in the home’s management. In the winter, this might include closing thermal shades at night and opening them in the morning. In the summer, it might be opening windows at night and shutting them in the morning.
Beyond passive solar, this home’s narrow, long design made daylighting much easier to accomplish. To minimize the energy used for artificial lighting, Brad and Linda installed LED bulbs in almost every fixture.
An efficient, well-insulated envelope is much easier to heat and cool, requiring minimal energy inputs. When supplemental heating or cooling is required, Brad and Linda rely on a small minisplit heat pump. Because they are ductless, minisplits avoid the energy losses inherent in conventional ducted central heating systems. And because each interior unit has its own thermostat, homeowners can choose to heat or cool only when rooms are occupied.
Brad and Linda were interested in using the sun’s energy as much as possible, and turned to active solar systems once they had maximized its passive aspects. They had met solar water heating (SWH) system installer Luke Frazer on a solar home tour and had decided, early on, that they wanted an SWH system for their home. With the relatively mild climate in Ashland, Frazer specified a drainback system for the couple. It was sized for an “average” household and designed for the amount of space available for the equipment. Because the system was planned before the home’s construction, Frazer was able to work closely with the contractors to keep pipe runs short and properly sloped. He also worked closely with their photovoltaic (PV) installer, coordinating the placement of the collectors with the rooftop PV array.