Passive Solar vs. Passive House

Passive Solar Design
Many of my clients express an interest in passive solar design for their home.  Passive solar design utilizes the free energy of the sun to provide heat for a building.  Typical features of a passive solar home include:

• Placement of the majority of the windows on the south side of the house
• Sizing of roof overhangs to control what times of the year and day sun can shine through the windows
• Placement of thermal mass, such as concrete slab floors or a stone fireplace, inside the home where it can absorb and slowly release the sun's heat

Passive solar design has been around since the 1970's, but we've learned a lot over the years.  Early passive solar homes often used an excessive amount of glass, resulting in overheating on sunny days and excessive heat loss at night and on cloudy days.  We now know that solar glazing should range between 7 and 12 percent of the total floor space (according to The Solar House, a classic passive solar book by Daniel Chiras).

​Passive House
Now there's a relatively new concept in environmentally friendly building called Passive House.  Passive House (called "Passivhaus" in Germany, where it began) is a rigorous voluntary standard for constructing  buildings which require ultra low amounts of energy for heating or cooling.  The energy savings is achieved through the following means:

• Very high levels of insulation in the walls, roof and under the concrete slab
• Extremely airtight construction, which prevents outside air from getting in and inside air from leaking out
• Use of high performance windows (typically triple-paned) and doors 
• Use of a balanced ventilation system to provide fresh air in a very controlled and energy-efficient way
• Using the sun's energy for heating during the winter and keeping the sun out during the summer

Designing a home to the stringent Passive House standards requires a comprehensive systems approach to building design, computer modeling and construction.  It requires extreme care in the technical design of the home as well as fastidious following of best practices during construction.  The higher initial cost of additional insulation, air sealing and more expensive windows and doors is partially offset by the savings from needing a much smaller heating and cooling system than would be required in a typical home in the same climate.  In addition, the owner will enjoy much lower operating costs over the life the home, although the payback period will be longer in a colder climate such as Wisconsin's than it would be in an area of the country with more moderate temperatures.