It’s time to say goodbye to the central premise of passive solar home design, which is using your windows as heaters.
Responding to Claire Spalding’s column in The Times-Independent from Feb. 1 (“Building Smarter”) in which she suggests limiting north windows, I ask, Claire, please let the people have their north windows — wherever they like, as large as they like (within reason), as appropriate to fulfill the real purposes of windows: views, light, and air.
The most even light and some of the best views are from north windows. Don’t require that windows contribute to your heat budget. And then let the people have only the south windows they actually enjoy; they needn’t have more.
Back story: Three years ago when my wife and I decided it was time to build an old-folks comfort home, I, wanting to do the right thing for the planet, and following the lead of several good friends, naturally assumed it must have a passive solar design. Mesmerized by the thought of working in concert with nature, harvesting “free” energy, I looked askance at homes that seemed to not take similar advantage. When attempts to get help from prominent solar experts failed, it became clear I would have to design it myself. All my many early designs featured large south windows and lots of thermal mass, and few north windows. I calculated ratios of south glass-to-floor area, included clerestory windows and Trombe walls, pondered moveable insulation panels, and planned for high heat gain windows on the south, all to absorb as much heat as possible while attempting to store that heat in thermal mass to prevent overheating.
Through it all I kept reading widely. The more I read the easier it became to separate real building science authorities from people repeating old truisms and politically correct assumptions. The wheels of my mind achingly ground round to the surprising, heretical conclusion that a passive solar design is not the best way to build a comfortable, environmentally responsible house. Building science has moved on; can Moab now do so too?
Yes, you can build a good house using passive solar design, and for some that will be the right choice. But it turns out that the better alternative for most is super-insulation (significantly higher than code-minimum levels), including high-R-value windows. If you lose very little heat in the winter (or gain very little in the summer), you don’t have to add much heat or cool much to be comfortable.
We now know how to do it, and it is cheaper than passive solar. Plus you will enjoy the advantages of thermostatically controllable heat instead of large temperature swings of a passive solar design. And ultimately your environmental impact will likely be smaller too.
People smarter than I have crunched the numbers and shown that the cost of buying and installing good windows beyond those desired for normal window purposes will not be recouped in energy, and the money could be better spent on insulation or solar panels. But the greater reasons for not following passive solar principles relate to occupant comfort: glare, chilly mornings, overheated afternoons even in the winter but especially in shoulder seasons.
Have you ever noticed that virtually no one sits on the south side of the Moab library or the Grand Center on a sunny winter day? Drive around on a sunny day even in the middle of winter and you will see that a large percentage of passive solar houses have the south blinds closed. It turns out that sun drenching, with its glare and high temperatures, is actually not so inviting in the long run for most people, and is not good task lighting.
Where do you go to get warm? Many people yearn for big south windows because they think they will need some warm place to sit on a cold winter day. But in a super-insulated house with really good windows, you’ll probably forget about that because everyplace is warm; you’ll just go about your business.