Green Means

A Passive Solar Design Matrix

By Shannon Scott,

Green Home Owner, Designer, Builder

            Kermit the Frog said, “It’s not easy being green.”  I like Kermit, but have to disagree with him on this point.  Building and living “green” is a lot easier and cheaper than people may think.  Building a green home, or living greener in an existing home, will save money, make you and your family feel better, and help to sustain the natural environment.

            Going green includes: increasing energy efficiency, using renewable energy sources, reducing fossil fuel dependence; using products that are sourced or manufactured using environmentally sustainable practices; and creating healthier indoor and outdoor home environments.

            My husband and I built our own energy efficient green home a few years ago.  I designed the home and the two of us built it with zero hired help.  We filled our 250 gallon propane tank in the fall of 2008 and just had it filled for the second time last month.  This made our average propane cost over the last three years $12.50 per month. 

            We use electricity from the grid, but the three primary factors that make our home efficient are passive solar, active solar, and energy efficient appliances and fixtures. 

            The most critical, influential element for energy efficiency is sound passive solar design. Passive solar differs from active solar in that there are no solar collectors, no moving parts, and no mechanical features – except maybe an attic fan.  Passive solar elements must work together in what I have termed a solar matrix.  Solar features will not be effective in isolation. A passive solar design matrix includes:

Southern Orientation

            If you are designing or planning to build a home, orient the longest wall along an east-west axis so that the wall is facing as close to true south as possible – within 15 degrees either way is good.   For our northeastern Nevada location, orienting slightly to the east keeps hot afternoon sun out during late summer and early fall.  Our home is oriented 12 degrees east of true south.  We capture grand views of the Ruby Mountains and the open spaces south of Spring Creek.

 Adequate Glass

            Glaze the south wall (glazing is another word glass) with 7-12% of the home’s total square footage. Windows must be energy efficient, low-E, double or triple paned, argon filled and not vinyl clad.  Windows that are vinyl clad on the interior give off airborne urea-formaldehyde and pollute indoor air quality.  I’ll write more about indoor air quality in a later column.  Use top quality wood windows with aluminum exterior cladding.  Good windows make a house.  Spend the money.  In our home the south wall has 11% glazing, 264 square feet of glass, which includes big windows and a couple of French doors.  This affords good winter sun penetration and connection with the outdoors.

Appropriately Sized Roof Overhangs or Eave Depths

            Sun is highest in the sky during hot summer months and lowest, traversing the southern horizon during winter. To keep hot summer sun out you need adequate or roof eaves depths.  Correct eave depths are based on the height of window sills off the porch or base of the wall, and the site’s latitude.  For our Elko location, about 41 degrees north latitude, with a sill height of 2 ft. above the floor, and an 8 ft. wall to the roof, eave depth should be about 2’8”. 

Thermal Mass

            Thermal masses are dense, medium to dark colored floors and walls that absorb sun’s heat as it enters south facing windows during the day.  The mass, such as concrete or tile, holds heat and radiates it back into the room after the sun has set.  We built a concrete slab 2 ft. above grade, and tiled the entire floor with Mexican Saltillo tile that is a medium terra cotta color.  6 inches of base sand, 4 inches of concrete (thicker on edges), and slightly more than 1 inch of tile make 11 inches of heat retaining mass.

Breeze Pathways

            In our high desert environment we don’t need air conditioning if we incorporate adequate breeze pathways throughout the house.  Floor plan layouts should allow breezes to circulate from room to room, or across rooms, so prevailing breezes flush the home with fresh cool air.  During summer months, windows should be opened at night and shut first thing in the morning.  Breeze pathways also help improve indoor air quality.

Beefy Attic and Wall Insulation

            Insulate the heck out of your attic.  Use R-50 or greater Green Fiber cellulose, Whisper Wool, Warmcel 100, Ultratouch, or other green, sustainably manufactured, family safe insulation.  We opted for Green Fiber insulation blown in deep enough to achieve a value of R-60.  Walls are 18 in thick, tightly compressed, straw bales for an approximate R-40 value. 

Reflective Roofing Material Color

            Roofs should reflect heat up, not absorb it into attic or living space.  Choose a light colored and/or reflective roof material.  We used ASC’s Galvalume.  It’s excellent quality, silver-grey in color, and fits well with our rural environment.

Tight Building Envelop

            Seal windows and doors well with non urea-formaldehyde caulk and/or weather stripping.  If there are unwanted drafts in a home find the source and seal appropriately with green, family safe, materials.  BioBased Insulation is a soy-based spray foam for spot sealing and other applications. 

Well Ventilated Attic

            If your home has a ridge vent do not install an attic fan, as it will reduce the draw effect of the ridge vent.  Attic fans make for cooler attic space so the heat does not migrate down into the home on hot summer days.

            These are the essentials of an efficient passive solar matrix, the single biggest step to living greener and saving money.  If you are an owner-builder, fear not and venture forth.  Your energy efficient home will be fabulous.
 

For questions, help designing a green, environmentally sound home, straw bale building, or how to incorporate more environmentally responsible choices into your life.  Just e-mail me:

deepgreenresults@gmail.com