Feature Article

The Hidden Science of High-Performance Building Assemblies

Any four walls and a roof make an enclosure, but for efficiency, comfort, and durability, those elements have to be meticulously designed and installed.

This typical wall section illustrates the materials chosen for the walls, roof, and floors.

Source: Siegel

For children, the delicate, fern-like patterns left by Jack Frost on the inside of a windowpane can be magical. But for the owners of a brand new commercial building in the Midwestern U.S., they were more like a nightmare.

“There were 71 punched window openings, all of which had condensation on the inside that turned to frost in the winter,” explained a consulting architect who was hired to diagnose the problem and suggest a solution. “They tried lowering the interior relative humidity to get the condensation to stop. That didn’t work.”

Interior condensation on glazing often indicates a problem with the window itself, but here the culprit was “a poor detail on the architect’s part,” explained the consultant. “They were trying to do this unique architectural feature where they had a steel element above the window that protruded to the inside.” Unfortunately, the steel was a thermal bridge, so no matter how well insulated and airtight the walls and roof might have been, those 71 “unique architectural features” spent the winter relentlessly chilling the rest of the building envelope. In the short term, a problem like this would likely cause major comfort issues and strain the mechanical system; because the condensation was not only on the glass but also on the window frame and the surrounding drywall, the thermal bridges also threatened the durability of the building materials. “The only solution was taking out all of the windows, cutting the steel that was the thermal bridge, and installing some additional insulation,” the consultant said. Fortunately, no lawsuit was filed. But with more attention to detail, the architecture firm responsible for this building design could have saved itself a great deal of time, expense, and embarrassment.

Residential Passive House Building Assembly – Exemplary Details

Illustrations: Steve Baczek Architect

High-performance buildings begin with a very complex big picture, integrating site-responsive orientation, climate-responsive form, hefty R-values, efficient mechanical systems, healthy indoor air, and glazing that effectively balances daylight and heat gain. But there’s more. In a reversal of the usual rule, the whole building can be less rather than more than the sum of these parts if attention isn’t also paid to hundreds of hidden components that we don’t talk about much. Things like corner joints. Window flashing. Hundreds of beads of sealant and runs of tape. Poorly designed, specified, or installed details in these areas can bring the proudest solar-powered building owners to their knees with moisture and mold problems, façades falling to pieces, and drafty interiors that send tenants packing—and even suing.

Published October 26, 2012 Permalink