Airtightness and Window Design: Is the Solar Design Obsolete?
Engineers are now coming to the conclusion that air-tightness is more important than window design in the conception of an energy-saving house.
According to the website for the Air Barrier Association of America, airtightness is gauged by measuring the building envelope’s effectiveness. But what exactly does air-tightness mean? Its technical meaning, unlike some terms that are specific to a profession, is the same as its colloquial meaning. Air-tightness is a measure of air infiltration and exfiltration.
Although air-tightness testing is not usually a construction requirement by government agencies, the States of Washington and California have testing requirements in place for certain situations, as well as the City of Seattle, the US Navy, and the Army Corps of Engineers.
Airtightness is being increasingly recognized as being of prime importance as a means of energy-saving within the green community. In an article for Treehugger, Lloyd Alter examines the emerging consensus regarding the importance of air-tightness in energy efficiency. He writes, “Everything I ever knew or said about green sustainable design was probably wrong…The new doctrine: high quality windows, tons of insulation, a tight seal and hey, while you’re at it, Passivhaus certification.”
Alter examines the doctrine of Frank Lloyd Wright and other energy-conscious designers, himself included, with nostalgia, outlining the description of a well-designed, energy-efficient house; its windows faced south, there were large eves that protected the windows in summer and embraced the low sun in winter; there was a high thermal mass floor that retained heat and released it into the room.
But then he confesses the ways in which this formula is self-defeating:
- High thermal mass floors are not that comfortable.
- The heat from sunny windows isn’t available at night or when the day is cloudy or foggy, when the heat is needed the most.
- A single-pane window can lose more heat than an insulated wall.
The rhetoric of the green community has been slow to respond to the advantages of air-tightness and insulation. Alter cites a 1978 study comparing a passive solar design, and the Saskatchewan Conservation House, which demonstrated the superiority of super-insulation and the lack of air-leaks over strategically placed windows and solar-mass floors.
So what are the defining factors of air-tightness? It is basically highly effective insulation with a good seal in all the aspects of the “envelope” of the house. Once the air is heated or cooled, it should be controlled. Even with thin windows, a well-insulated house that retains its heated air will save more energy than a solar design with triple windows, thin insulation, and air leaks.
Alter claims that the size and scope of the windows should focus on the aesthetic and practical uses of the house, not the energy requirements. More important is the insulating factor of the windows, to counter-act the tendency of glass to lose heat by providing double (or better yet) triple panes. Also, as discussed at the site, Efficient Windows Collaborative, e-glass coatings can reduce “emittance,” thus improving the insulating properties of a window. Krypton or argon gases can be used to fill double or triple windows, which can push the insulating capability even higher by reducing the transfer of heat from the inside to the outside of the house.
Sealing the house is an important part of energy control. In addition to common sealants such as caulking and weather-stripping, more comprehensive methods of air-tightness will depend on the humidity of the area, the temperature, and whether or not the home is an existing structure or new construction. Air barriers and vapor barriers will give a significant boost to controlling conditioned air, as discussed on the site, energy.gov.
Despite these pitfalls, Alter hasn’t abandoned solar design. He claims that southern orientation is still good if you plan on installing solar panels. He also recommends Passivehaus certification, which includes a ventilation system with heat recovery.
Watch Dr. John Straube discuss the importance of airtightness and how it’s critical for maintaining a building’s performance.
Dörken delivers innovative, high-performance air and moisture barriers for commercial and residential construction sold under the DELTA® brand name. A North American manufacturer based out of Beamsville, Ontario, Dörken Systems Inc. is a subsidiary of Ewald Dörken AG, a leading European developer and manufacturer of waterproofing and drainage products sold worldwide. Dörken is known for delivering premium products while providing educational programs and full technical support. For more information, call 1-888-4DELTA4 (433-5824) or visit https://www.dorken.com/en/