Basic Ideas in
Passive Solar Buildings

Natural Forces At Work For You
In any climate, a building can make use of free heat from the sun. An elementary passive solar heating concept is letting in the sunshine with windows, then keeping the resulting heat inside with insulation and thermal mass. The goal in passive solar building is the optimal balance of mass, glass, and insulation for a particular site and house design. A well-designed solar home in Oregon's Williamette Valley can get up to 30 percent of its winter heating needs met at no cost.

Passive Cooling
Passive cooling requires correct placement of windows, proper shading of windows by trees or constructed shade, light-colored roofs and walls to reflect heat, nighttime ventilation, and thermal mass to prevent overheating in hot, sunny weather. Large west-facing glass areas usually present a risk of unwanted summer afternoon heat gains. Air-conditioning is unnecessary in the maritime Northwest, if the house is properly designed.

Choose The Right Building Site
The more southern exposure, the better the site for passive solar. A steep north-facing slope, or large trees or other buildings in the wrong places will cut back on your solar window. Protective berms, natural slopes, and thick tree cover to the north side block cold winter winds and help create a warmer microclimate around your house. See the Energy Outlet handout on landscaping and house siting.

Let The House Face The Sun
It is very important to orient the long axis of the house east-west, so that as much wall and roof length faces directly south as possible. The most livable homes group the kitchen and dining room to the east, for morning light. Clerestory windows and dormers can bring winter light into otherwise dark areas of the house (minimize skylight use). Use a solar path chart to design a building so that low winter sun shines in and high summer sun is blocked by effective use of windows, overhangs and shade.

South-Facing, High Quality Windows
Passive solar houses have large window areas on the south side where the sun comes from, and minimal windows on the north side. Some sites will suggest minimal west-facing windows (SHGC<.40) as well. Window specifications should be tuned for the window location; use softcoat LowE (lower SHGC) on north, west, and possibly east-facing glazing, and hardcoat LowE, or maybe uncoated windows (.55 or higher SHGC) on south-facing glazing. You should be able to get windows with U-values below 0.32 without much difficulty by using warm-edge glazing spacers, LowE coatings, and inert gas fills.

Superinsulate, Build Tight, Ventilate Right
High R values and minimal air leakage are the most important factors in building any low-energy house. The Oregon Energy Code is a minimum, not a maximum. There is no such thing as too much insulation, only practical difficulties in implementation! Blower door test to verify house tightness. Invest in a high performance ventilation system; an air to air heat exchanger recovers the heat in exhausted ventilation air.

Thermal Mass
Thermal mass inside a building moderates temperature swings by storing heat when the sun is shining and releasing heat back into the building when it begins to cool off. Materials commonly used for mass include water, concrete, masonry, and earth. Keep the mass at 3-4” thick, and keep it in the direct sun for best effectiveness. Mass must be carefully balanced with glazing area to perform properly in a given climate.

For The Best Passive Solar Design
Time spent on the building site observing sun, wind, rain, and ground water pays off in selecting the ideal location and design for the house. A solar building energy modeling software program such as Energy10 allows a solar building design optimized for the local climate. Earth-sheltering reduces heat loss and thermal swings. Build an airlock for exterior doors. Select materials carefully for durability and lack of toxicity. Integrate the heating and ventilation systems into the overall building design. Provide space for solar/mechanical equipment, and extra pipe and conduit runs for future solar system expansion. Check with the Oregon Office of Energy for a tax credit review. Above all, BUILD SMALL to minimize overall resource use.

Copyright Alan Van Zuuk