FENESTRATION: SPARE NO EXPENSE
Driven by initiatives such as the U.S. Department of Energy’s High Insulating and Low-E Storm Windows Volume Purchase Program, triple-glazed window units are gaining popularity in the residential marketplace.


With such a wide range of window/door manufacturers and products to choose from—not to mention a wide range in cost and performance—it can be quite a trick to capture the best value for fenestration specifications.


“We do not believe in spending a lot of money to gain nominally better performance,” admits Raymond Pruban, chief manager, Amaris Custom Homes, Minneapolis. Similarly, Mark Wahl, co-owner, Cobblestone Homes, Saginaw, Mich., acknowledges that it’s a matter of cost and aesthetics vs. energy performance, so for their baselines homes, they typically install wood or vinyl double-pane, argon-filled, low-E windows with a U-value of 0.30 or less. However, when it comes to highly efficient, net-zero homes, then triple pane, high performance vinyl windows with spectrally selected glazing and a U-value of 0.20 are required.


On the other hand, Miloš Jovanović, co-founder Root Design Build, Portland, Ore., sees performance as the bottom line when specifying windows and doors because they are the weakest points in the envelope. “In order to achieve the desired performance for most temperate to cold climates, the windows need to have three panes of glass and a heavily insulated frame.”


Building in a colder, Northwest climate, Jovanovic needs that U-value to be down around 0.14 and has only found European manufacturers that can offer that level of performance.


In a similar vein, because so much time is invested in creating a thermally efficient wall system, Tom Reid, owner, Green Home Construction, Hood River, Oregon, points out that air leakage through windows and doors is where his team focuses its energy.


“If you do a heat loss calculation, your best return always is eliminating air leakage, so we try to stay away from window designs that tend to leak air more than others, such as sliders and double hungs,” he explains.


 


Taking a different approach, Reid is a big fan of the double stud wall. “This eliminates most thermal bridging and provides for a much larger cavity to fill with insulation.”


At the same time, this method can be more costly, so a more affordable alternative might be to run 2’ x 2’s horizontally across the interior face of the studs at 24” on center, leaving a smaller cavity.


However, in cases where the studs aren’t taken care of by the cavity insulation, then products like rigid foam insulation or polyisocyanurate rigid insulation can be used to cover the studs to eliminate thermal bridges.


Let the Sun Shine In
While a big part of the passive house equation is to fully seal and insulate the shell, the other key is to maximize free sources of heating and cooling, namely solar heating and natural ventilation.


While a fully passive solar-heated home requires a long and narrow floor plate, this type of architectural look doesn’t always blend into a typical suburban setting, so Pruban’s group tends do as much as they can to maximize solar heat gain while not going that “full nine yards.” Still, this includes a south-facing lot, colored concrete floors for increased thermal mass and a higher U-value for the windows.


Another important component of passive heating is to design shading for the summer months, as passive solar can easily lead to overheating.


“Many strategies can be used for summer shading, but an exterior shade/blind is the most effective,” says Jovanović. “A great way to provide shading to the south-facing windows is to plant a deciduous plant on a trellis, which loses it leaves just in time for the heating season.”


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