If the sun arcs to 35 degrees above the horizon at noon on December 21 and your living room windows face south, how much do you pay for heat that month? The question might sound hopelessly inscrutable, but not to Washington, D.C.-based designer and remodeler Alan Abrams, CPBD (certified professional building designer), who carried out such calculations when he was designing this green addition in Silver Spring, Md.
The west elevation shows the sun and shadow at 4 p.m. on approximately August 5 and May 11 at 39 degrees latitude, 77 degrees longitude.
Using the principles of passive solar design, Abrams relied on the orientation of the site and its access to sunlight to dictate the shape of his plan. “The geometry of this addition was not derived from the existing house,” Abrams says. “As soon as we got out from the back wall, we readjusted the geometry to present the longest wall with the largest windows to the south.”
Abrams carefully designed roof overhangs on both the first and second floors to provide shade in summer but not in winter. “While there's no direct solar gain in the warmer months, there is full solar gain from the south in the coldest months to heat the home naturally, and varying degrees of solar gain in the intermediate times.” Abrams also built cross ventilation into the design wherever possible, improving air circulation in warm months. These measures significantly reduce utility bills throughout the year.
Abrams says that using SketchUp — a design application — greatly eased the design process. The software's shadow study feature allows him to carry out minute adjustments in the size and position of the roof eaves and overhangs with simple mouse clicks and drags. “Sketch-Up is absolutely ideal for this application,” Abrams claims. “You can set up solar tracking for any given latitude, and it's very easy to manipulate geometric forms.”
This photo shows the deciduous tree canopy that — in addition to the eaves overhang of the house — mitigates late afternoon summer sun.
Credit: Kenneth M. Wyner
Abrams incorporated other green systems into his design, including Icynene solid foam insulation, the use of Parallam beams instead of older-growth timber, EPA's Energy Star-rated fiberglass windows instead of vinyl, highly efficient heating and air conditioning equipment, and Energy Star-rated reflective roofing.
Abrams says that homeowners are best served when they weigh the up-front costs for these systems against the long-term savings that accrue from paying lower energy bills. And, he notes, passive solar design typically does not add to the cost of construction; it merely requires awareness and careful effort on the part of the designer. “The wonderful thing about passive solar design is that it doesn't cost you one extra dime to place your windows with the proper orientation,” Abrams says. “The ‘green' in green building also refers to the color of money: Environmentally conscientious design always provides a good return on the investment.” —David Zuckerman is a former assistant editor for REMODELING.