Space heating and cooling account for approximately 50% of home energy use. A properly designed passive solar structure can use up to 90% less energy. We can provide consulation on ways to build and add passive solar spaces. Some passive solar design principles to consider are:

• Orient the long axis of the structure east/west. This allows maximum solar gain through south facing windows, and can include a large south facing roof surface for solar hot water and photovoltaic arrays.
• Size roof overhangs to shade south facing windows completely during summer months (May through Sept), while still allowing maximum solar gain in winter.  Roof overhangs ratio for this latitude (per NREL):
      if window height = 1.0
      then vertical distance from top of window to overhang = .326
      and overhang = .754
• Limit window square footage to no more than 10% of floor square footage (skylights count double, but "solar tubes" do not count), and have minimum windows on east/west aspects, and none, if possible, on north aspects.
• Windows should be double pane. Glazing on south facing windows should be plain glass, not low-e, since low-e limits heat gain in winter by up to 60%. Shade these windows with overhangs to prevent summer heat gain. East or west facing windows should have low-e film on the third surface (outside surface of inside pane) for best year round performance. Metal clad wooden framed windows are the most effective and maintenance free.
• Super-insulate (at least double code requirements.) This can be done in a variety of ways -- SIP (structural insulated panels), double walls, solid foam, earth berming, etc. Insulate windows at night with thermal blinds, such as Window Quilts® (tracked insulating shades) or Warm Windows® (quilted roman shades.)
• Include thermal mass inside the insulated space to moderate temperature swings.
• Use deciduous plants or exterior shades to shade east and west surfaces in summer, but allow solar gain in winter. Exterior shades are more effective than interior shades because they stop solar gain before it enters the structure.
• Use openable windows to allow cross ventilation without undue heat gain or loss. Use a whole house fan or heat exchanger to insure good indoor air quality in winter.
• Use an air lock entry way to limit heat gain in summer and heat loss in winter.
• When building a new home, make it "solar ready" by pre-plumbing for a future solar hot water system, and placing conduit for a future photovoltaic system.