Solar orientation is another key ingredient. This house’s most striking feature—that 23-foot-tall wall of south-facing glazing—is a show-stopper, but it’s also one of the most important pieces of equipment. In winter, when the sun is low in the sky, the monumental window allows the house to draw the sun’s warmth inside, where it commingles with heat generated by appliances and body heat. “The key is to have high solar gain on the south windows while also having a high R-value in all of your windows to retain the heat inside,” Wedlick explains.
In summer, when the sun’s position is higher, the window configuration achieves the opposite effect. Deep overhangs block the sun’s rays from above, and the home’s super-insulation keeps its interiors cool. At this point, extra high R-values in the walls, roof, and floor reverse roles and help to offset the need for conventional A/C. As cool temperatures are absorbed into those mass walls, they take on cave-like properties, maintaining a comfortable temperature inside. Thermal window shades on both ends of the house also help control heat loss and gain, depending on the season.
High or Low? The sun's position changes with the seasons, and this house exploits that natural phenomenon. Come summer, when the noon day sun is high, deep eaves provide shady cover. In winter when its position is low, generous glazing invites its rays inside. During transitional months, the angles allow some solar gain, but not too much.
Credit: Dennis Wedlick Architect
The Envelope Please Structural insulated panels (SIPs) form a tight cocoon, allowing the house to maintain temperate internal conditions year round. To further reduce the potential for thermal bridging, the construction team mapped out and sealed up all the spots where materials and components come together.
What the typical custom home spends on souped-up mechanical systems, this house invests in its envelope. Its timber-framed skeleton of glulam trusses is skinned with SIP walls and double-paned windows with a transparent layer of vinyl between the panes. And here’s the real kicker: The slab foundation and roof are heavily insulated too. Pouring the concrete slab on top of high-density rigid insulation improved the floor’s insulation values by 600 percent over conventional construction, Stratton says.
To seal the deal (literally) the construction team used caulk, tape, and tight joinery to minimize thermal bridging in areas that are typically prone to heat gain and loss, such as sill plates and planar edges where walls meet up with the roof and foundation.
The end result is a monolithic shell that functions as one colossal thermal mass. “None of the structure of the house touches the outside,” Wedlick points out. The prefab walls are R-50, the roof is R-53, and the slab-on-grade concrete floor is R-60.
Now that's a tight thermos.
Retention Strategy Rather than automatically generating heat, the house focuses first on maintaining the temperature it's already captured inside. A heat recovery ventilator gets rid of stale air, but not before mining it first to extrapolate its thermal energy.
The structure does have an HVAC system, albeit an atypical one. Its essential mechanism is a heat recovery ventilator (HRV)/air exchanger that brings a constant influx of fresh air inside the home while ensuring that comfortable conditioned temperatures (be they warm or cool) aren’t wasted and expelled through exhaust airflows.
“With the HRV, the incoming air basically ‘steals’ heat from the outgoing air as it passes through a heat exchanging chamber,” Wedlick explains. “This constant pull of fresh air gives a passive house dramatically better air quality than a conventional home, even though it’s tightly sealed. In winter, the HRV is the home’s primary heat source in the sense that it’s providing the most efficient recovery of heat.”
As a backup, the house is also equipped with two point source electric heat pumps for supplemental heating and cooling needs, plus electric baseboard heaters in the master bedroom and main living area. But Wedlick believes much of this is over-engineering. "I'm predicting that only one of the two heat pumps will ever be used for heat," he says.