What Works

The original design contained some basic passive solar design principles using "off the shelf" materials. Based upon the experience of the last 20 years, we now know that these basic principles and materials work very well. This and the many other solar projects we have seen and read about have taught us the following:

  • A good quality design is imperative: too much or too little glazing, glazing in the wrong area, too much or too little mass or mass in the wrong area, plus many other considerations are critical. Failure to understand these principles and apply them properly are a guarantee for failure.
  • Good insulation is very important but today's insulation standards may be enough: we used 5.5" batt fiberglass (R19) insulation in the walls; we used 10" fiberglass batts (R30) in the cathedral ceilings.
  • An understanding of the sun's path at various times of the year and in any one particular location is imperative for a good design. For example: the sun's angels are much lower in Seattle than in Tucson, and the house must be designed to capture the sun's rays during the heating season and shade them during the cooling season.
  • A direct and open unobstructed southern exposure is required for heating purposes, yes, the structure must have an unobstructed wintertime southern exposure (unless the house is south of the equator). Some deciduous trees can be used to shade summer sun.
  • Most of the windows must face south, a few can face east and west, very few should face north.
  • Concrete, concrete block, tile and brick work well as a mass to absorb the heat. While absorbing the sunlight such mass prevents the space from overheating (unlike a closed car in a parking lot). When the sun goes down, the mass slowly releases the heat and lengthens the period of solar heating time.
  • An open design helps the heat to circulate.

Designing for passive solar heating

by Audrey Van Horne, Architect

There is a lot of pleasure in living in an a solar house, the solar heating provides a comfortable even heat and often some sunny places to enjoy. It takes a bit of adjusting one's life style; things like - 'don't leave the door open when it is chilly outside; draw the curtain over the glass in the evening when you want to keep the heat in.'

Planning is required if passive solar heating is what you want. The building needs to collect sun from the south, (because that is where the sun is. ) So building in a location that has access to the south sun is a primary need. There are lots of elements that have to be adjusted to gain the heat - things such as how much window to collect the sun, and an area - a wall or floor (or both) to collect the heat - or get warm when the sun shines on it, and finally a way of moving that warmth to other parts of the house.

Unless there is circulation of the air throughout the house, the solar space can get very much too warm, and other spaces wont get warm unless there is a way for the warm air to move into the rest of the space. Trapped warm air will make the space much too hot on a sunny day. Warm air will rise - so a two-story circulation path will work the best. And openings must be planned to create the circulation path.

All this planning is part of the design of the house. And yet, the design must first serve the needs of the occupants or family who lives there. The layout of the spaces is primarily for the function of the family, but it must be adjusted and planned for passive solar heating if solar heating is the goal. The capability to design and integrate the solar heating into the plan for the house is a skill that architects are trained to do.

The overall design addresses the house plan and the location on the property to gain the sun, and surfaces to collect the heat from window openings located to capture the sun. The flow of air, the location of other windows, the type of heating for the house, the materials used for the storage of heat - or the mass - are all part of the design and plan.

Good design results in a very livable house that has been laid out to take the best advantage of the sun and the heating potential.