Walls and Roof

The insulation strategy at the Benker residence focused on durability and a robust building envelope.

Subslab assembly

5" of FoamGlas under slab (R-3.4/in)

Subslab R-value 17.0
Slab edge R-value 20.0
Foundation wall assembly

The foundation wall is a Thermomass centrally insulated foundation with a total R value of 20. This was the best option, when compared to an internally or externally insulated foundation. There is no foam on the exterior of the foundation wall which eliminates the issues of mold, trapped condensation, loss of internal space, a fire hazard, insect/animal infiltration and other possible damage. Owens-Corning Foamular XPS insulation was at the foundation because it is GreenGuard certified to be durable and low-emitting.

Foundation wall R-value 20.0
Above grade wall assembly

This 2x6 wood framed wall has blown fiberglass in the wall cavity. On the exterior side of the wall 2.75" of mineral wool provides continuous insulation, taped ZIP sheathing creates a continuous air barrier and vertical strapping creates a rain screen. The stud framing employed open corners for a better thermal envelope. It is designed to the 2012 IRC wind loads.

Above grade wall R-value 35.0
Cathedral ceiling assembly

5" closed cell spray foam was applied to the interior side of roof decking, then6.5" blown in fiberglass was added to the interior of that.

Cathedral ceiling R-value 58.0

Windows and Doors

Window Assembly:

All windows are triple pane and have a low u-value. Windows were chosen by their solar heat gain to maximize winter solar heating and decrease summer cooling requirements by changing the solar heat gain coefficient of the glass depending on the direction of the window. North-, east-, and south- facing windows all have a high SHGC-0.36 while the west-facing windows have a low coefficient (0.16). U-values range from U-0.23 to U-0.26. Windows are triple glazed, argon filled, and wood framed.

Average window U-factor 0.26
Solar Heat Gain Coefficient 0.36

Mechanical Systems

Space cooling - Manufacturer & Model 36k Vertical loop Waterfurnace 7-Series Geothermal System, 29.5 EER
Space heating - Manufacturer & Model 36k Vertical loop Waterfurnace 7-Series Geothermal System, COP 4.4
Domestic hot water - Manufacturer & Model Desuperheater in summer, Desuperheater for preheat and AO Smith Heat Pump in winter
Ventilation - Manufacturer & Model Venmar Eko ERV
Lighting Manufacturer and Model 100% LED interior and exterior lighting
Lighting Efficiency
Mechanical Equipment Installation Details and Comments

The vertical geothermal system has 2 wells with 9 gpm loop flow. PEX tubing and an on-demand water heater recirculation system are used for water heating to minimize heat loss.


Air Changes per hour, ACH50 0.57 ACH50
Air Changes per hour, CFM50 385.00