The Diagon Alley passive house in Colorado | WorkshopL

This small house in Steamboat Springs, Colorado combines modern design and a cutting-edge super-insulated building envelope with a traditional exterior appearance. As its name suggests, the Diagon Alley house sits just off the lane at the rear of its lot. Designated as an accessory unit under Steamboat Springs’ zoning bylaws, there will eventually be a second house built at the front of the lot. The Diagon Alley house was designed by architect Erik Lobeck of WorkshopL, a Colorado firm focused on ultra energy-efficient design and construction.

The house has a simple gable-roofed building form. It is clad in an attractive combination of reclaimed boards and metal siding. Besides the aesthetic appeal, the metal also serves a functional purpose. Skirting the bottom of the house, it protects the wall from the splashback of roof run-off hitting the ground.

The living room, a spacious kitchen and a small powder room are on the main level. Although there doesn’t seem to be a dedicated dining space, a dining table could replace the kitchen island if desired, and still leave a good amount of counter and cabinet space. The two bedrooms are upstairs, along with a full bathroom and a laundry closet. Although the house has two bedrooms and one and a half bathrooms in only about 650 ft² (60.4 m²) of interior living space, it doesn’t appear at all cramped. One reason for that is that the space is used very efficiently. Aside from the staircase, there is very little dedicated circulation space. The stairs are placed so that they land in the middle of the upper floor, allowing the upstairs hall to be kept very short. Creative solutions also play a role. One example is in the living room, where the fireplace and TV were recessed under the stairs so they wouldn’t protrude into the room.

The Diagon Alley house was designed to use very little energy. WorkshopL followed the Passive House methodology when designing the house, using computer modeling to ensure the home would perform well and be comfortable in all seasons. For example, the modeling was used to size and place the windows to allow a modest amount of solar gain in winter, but without overheating the home in summer. The Passive House approach to energy efficiency relies largely on “low-tech” methods — insulation, sealing air leaks, window placement and shading, etc. — rather than on mechanical equipment.

Entering the Diagon Alley house, one of the first things you might notice is how thick the walls are. WorkshopL started by building fairly standard 2×6 stud walls with fiberglass batt insulation, but then proceeded to add 8″ of EPS foam on the outside. The result is a total wall insulation value of R-50. The roof and foundation are likewise built with extreme levels of insulation, R-90 and R-50 respectively. Triple-paned windows complete the thermal envelope. With so much insulation, very little heating is required to keep the house warm, even during Steamboat Springs’ bitterly cold winters. There are a few small electric radiators for backup, but the gas fireplace in the living room is sufficient to heat the whole house.

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Images courtesy of WorkshopL.

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