Passive Solar and Energy Efficient Home Design
Every home is a solar home
It is a fact that everything we build is solar. When we ignore solar energy during the design stages, we end up with a building that may benefit from solar, though it is just as likely to be beat up by solar energy.
A passive solar design will not only lower your utility bills, it will be comfortable. Comfort is priceless.
The following guidelines are drawn from research and practical application, from successes and failures, from the experience of our ancestors who lived in caves, and from recent computer-generated studies.
Orientation
The longest wall of the home should face south. The winter sun rises south of east and sets south of west. Placing more glass on the south wall will ensure that your home receives free solar energy.
This same orientation helps to prevent the high summer sun from entering the home.
A compass will point to magnetic north/south, but a solar home or collector works best when it faces true south.
In the El Paso area, true south is 12 degrees east of magnetic south. This declination from magnetic south varies across the country depending on longitude.
Solar Access
Buildings or trees too close to your home could block the low winter sun.
Windows
The amount of glass on the south wall may equal 7% of the home's total square footage. For example, 2000 sq. ft. = 140 sq. ft. of glass.
To avoid overheating, this amount of glass should not be exceeded. The 7% applies to convention home construction with standard floor coverings such as carpet, vinyl tile, or wood. Increasing glass area above 7% will require additional thermal mass, e.g. concrete/tile floors, rock, brick, concrete or adobe walls.
The 7% amount is net square footage or total window area less the trim, etc.
Multiply the entire window by 0.8 to get the net glass area. For example, a 3'0" x 5'0" window is 15 square feet. 15 x 0.8 = 12 square feet net.
East and north glass should be limited to no more than 4% of total square footage. West glass should not exceed 2% of total square footage.
Landscaping
Plant deciduous or evergreen trees on the east, west and north sides of the home. Xeriscape!
Avoid dark colors, inside and out.
Insulation
Insulate exterior of slab/foundation with extruded polystyrene sheets. R-5 for moderate climates, R-10 for colder climates.
Sole plate: Install sill sealer under the bottom plate of all exterior walls, on both the first and second floors.
Walls: In moderate climates, use 2x4 frame walls with R-13 batts and R-4 rigid insulated sheathing boards (1" expanded polystyrene). For cold climates, use 2x6 frame walls with R-19 batts and the same R-4 sheathing. Sprayed cellulose insulation should be considered because, though more expensive than batts, it is more effective because it fills voids and reduces air leakage.
Important: Prior to installing wall insulation, use cans of expanding foam insulation and/or caulk to seal all electrical and plumbing penetrations around doors and windows.
Attic: Install R-30 insulation for moderate climates, with a blown in type preferable. Levels of R-38 to R-50 are recommended for colder climates.
Ductwork: Tape/seal all joints in ductwork. Ductwork should be installed in interior (heated) space so that heat or cold is not lost to unheated spaces (attic). Furrdowns should be sheathed and sealed prior to installing duct. Insulate walls surrounding furnace closets and seal the return air plenum.
Doors: Install steel or fiberglass insulated exterior doors that have an insulation value of R-5.9 or greater. Lower R-value doors can be used in conjunction with a storm door.
Ventilation: Place and size windows to take advantage of natural ventilation and prevailing breezes.
Fans: The use of ceiling fans can drastically reduce the running time of air conditioners.
Contact your local county agent or state energy office for recommendations specific to your area.
