Robert J. Kobet, LEED Faculty
One of the great things about being involved in the green building movement is the energy and enthusiasm – the passion, really – that most of my colleagues and clients have for the ongoing dynamism of the state of the art. Having practiced for thirty-six years it is as interesting to look back and see where we have been as it is exciting to speculate about the future.
A good example of this is Lloyd Alter’s October, 2015 article in Treehugger titled Everything I ever knew or said about green sustainable design was probably wrong. In it he addresses classic passive design versus super-insulated homes and the Passivhaus approach to building resource efficient structures. He contends the drawing below, or some version of it, has been part of every sustainable design class since about 1970: lots of south facing windows carefully shaded by properly designed overhangs, with the winter sun heating up that thermal mass of the floor. But what if we were all wrong, he asks? Or, as I prefer, what now, given how much we have learned?
Green Building Advisor Martin Holladay looks at what was almost a religious doctrine and questions its tenets, writing:
…certain aspects of the passive solar approach – an emphasis on careful solar orientation, a concern for proper roof overhangs on the south side of a house, and a preference for south-facing windows over north-facing windows – seem embedded in my DNA. Lately, however, I’ve begun to wonder whether there is a technical justification for these recommendations. Do these design principles result in energy savings? Or am I just dragging around the stubborn legacy of my hippie past?
Martin contends high thermal mass floors are not particularly comfortable, and south facing windows as an energy source are counterproductive and “should be limited to that necessary to meet the functional and aesthetic needs of the building.” Essentially, careful orientation doesn’t matter because the extra solar gain isn’t needed. Large expanses of south-facing glass help heat a home on a sunny day, but the heat gain doesn’t come when it’s needed. Most of the time, a passive home has either too much or too little solar heat gain. So, much of the solar heat gain can be wasted. At night, and on cloudy days, large expanses of south-facing glass lose significantly more heat than an insulated wall.
So, what has changed? Insulation and sealing. Holladay quotes building expert Joe Lstiburek:
We were here in the late 1970s when ‘mass and glass’ took on ‘superinsulated.’ Superinsulated won. And superinsulated won with lousy windows compared to what we have today. What are you folks thinking? Today’s ‘ultra-efficient’ crushes the old ‘superinsulated’, and you want to collect solar energy? Leave that to the PV.”
Saskatchewan conservation house – a departure from “mass and glass”
Alex Wilson of BuildingGreen came to the same conclusion a few years ago, going from imagining in the 70s “in our youthful idealism, that within ten years all new houses would be oriented on East-West axes and rely on south-facing windows and thermal mass for heating.”
I can’t argue the science of what these experts are contending regarding only energy efficiency. However, there are variations on the theme I believe are worth mentioning. Earth integrated architecture, often constructed of reinforced concrete or masonry, clearly has much more mass than the available (south facing?) window area can justify. However, earth integrated architecture features very high equivalent R-values and very low infiltration if constructed properly. The combination of “mass and glass” and earth integration makes them very energy efficient, quiet, and non-combustible. They feature living roofs and minimal maintenance. Their slab on grade construction is wonderfully compatible with radiant floors; something I find very comfortable. And, the estimated life of reinforced concrete is 1500 years, which offsets the argument concrete is energy intensive, while providing resource efficient housing for many generations to come.
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