By simply orienting your house in respect to the sun, you can save from 30% to 50% in energy costs. But if you're building on an urban infill lot or in a suburban subdivision, your site design options may be limited by lot size and the direction the house is required to face. Other controlling factors can be CC&R’s, neighborhood design standards, setback requirements and sun-blocking objects on adjoining lots. While you can compensate for lack of passive solar with other measures, it's more expensive to built and condition a house if you're fighting against nature rather than moving with it.
Sustainable House Plans can be altered or reversed to take better advantage of actual site realities. At a minimum, it it best to pursue the concept of "Sun Tempered", which means 1) the long axis of the house is oriented south and that, 2) the south facing windows are optimized for solar gain in the main living areas. More Passive Solar design measures can be added, such as heat absorbing floors and windows tuned to your specific location. The following list are measures that you can add to plans in order to enhance passive solar.
Having the windows on the long side of your house face within 15 degrees either direction of true south, is ideal for passive solar heating. The object is to pick up solar heat gain in the cooler months, but it requires that you limit heat gain in the warmer months. It is best to limit the windows on the north side of the house to minimize heat loss in the cold season.
Limiting solar heat gain is accomplished by shading with, deciduous trees (they shade in the summer and lose their leaves in the winter, allowing the sun through), eaves (you can alter building plans and extend eaves in certain locations if you predetermine the sun angle in your location), awnings (awning can be constructed over specific windows as decorative elements, and adjusted for length as per required sun angles) or trellises (trellises can be covered with deciduous vines that shade in the summer and lose leaves in the cold season).
To find the amount of shading required, look up the sun angles in your location for Dec. 21 and June 21.* With these angles you can determine the required extent of eaves or awnings and the height and amount of deciduous trees. The object is to see that nothing blocks the sun from coming in the window at noon on Dec. 21 and that the window is completely shaded at the same time on June 21. See the Sun Angle Detail below for amount of shading required by season. Adjust your eave and awning extensions and your tree planting accordingly. Below the Sun Angle Detail is a link to Passive Solar Design tools.
For Sun Tempered Design, the windows on the south facing side of your house should not exceed 7% of the total living space. When you know the orientation of your house, you may want to alter window size to conform to these percentages. Note: changing size and placement of windows can require revision of lateral bracing and may affect some green certification requirements. Window egress requirements for bedrooms must be maintained as well as light and ventilation requirements. Generally, for natural lighting, glazing is required to be 8% of the floor area and 4% of the floor area for ventilation for each room affected.
Generally, it is best practice to have the most used living spaces, such as living room, family room, kitchen or home office on the south side of the home where they will take best advantage of natural light during daylight hours. Often this can be accomplished by building a plan in reverse. Opened interiors are conducive to passive solar because they allow natural heat and cooling to circulate. Operable, upper windows (clerestory windows) are desirable because they enable you to allow excess heat to escape and can permit light and heat to reach parts of the house which are not located on the south side of the house.