Low Energy, but High Impact

The Passive House system, a design and construction concept with considerable traction in Europe, begins to take hold in the United States.
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From Architectural Record
Michael Cockram

"Shading and ventilation become crucial in this climate," Saft says. He oriented south-facing windows to take in the predominant winds on the ground floor. A bank of north-facing windows, placed high in a double-height space, takes advantage of cross and stack ventilation. All windows are protected with exterior shades and the exterior is clad with a "rain screen." In this typical Passive House detail, vertical furring strips are attached to exterior rigid insulation so that there is a gap between the insulation and the siding. The space provides a channel for water to escape. But Saft found that venting the space at both the top and bottom dissipates a substantial amount of heat. "On the south elevation I measured a 20 degree temperature drop from the siding to the insulation layer," Saft says. "The rain screen is essentially a whole house-shading device."

In this climate zone, the glazing should generally have a low Solar Heat Gain Coefficient (SHGC), which means that the glazing is treated to limit the amount of solar heat transmitted to the interior of the building. The lower the SHGC, which is expressed as a fraction between 0 and 1, the less heat is transmitted. On the Saft house, the SHGC is around 0.29 on all windows. But a Passive House designed for New England, where heat gain is desirable for much of the year, might use glazing with an SHGC of around 0.64. Projects that maximize solar heating in the winter but control heat gain in the summer will sometimes use windows with a high SHGC on the south facade (where the windows can be easily shaded in the summer months) and low SHGC on other orientations where sun controls aren't as effective.

Foundation Thermal Study
Albert, Righter & Tittmann Architects markedly decreased heat loss through the foundation of a house in Charlotte, Vermont, by providing 12 inches of rigid insulation under the slab and 10 inches along the perimeter walls

Source: Albert, Righter & Tittmann Architects


Annual Energy-Use Analysis
For the Vermont project, Albert, Righter & Tittmann studied the cumulative energy savings achieved through the deployment of an array of Passive House strategies.

Source: Albert, Righter & Tittmann Architects

 

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Originally published in Architectural Record
Originally published in April 2011

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