Last week I wrote about a centuries-old style of home that ticks most of the boxes for good house design. The New England Saltbox can be said to be an early example of passive solar design, which takes advantage free heating by sunlight during winter months.
The obvious first requirement of passive solar design is to have more windows facing the equator than facing the poles (depending on which hemisphere the structure happens to be located in). Windows are both an asset and a liability to a warm home. When winter sun shines directly through glazing a house is warmed, but when it does not, windows release warmth to the outdoors.
In our region, south-facing windows lose heat more or less all the time between May and October. Even north-facing windows lose heat during winter nights, which happen to last 14 to 16 hours. From this perspective, window placement is key to passive solar design.
Taken to the extreme, a passive dwelling could have glazing on the entire north side and none to the south. This is exactly the type of structure I encountered a decade ago in Ladakh, India, although the orientation was reversed for the northern hemisphere.
The region of Ladakh lays mostly between the Himalaya and Karakoram Mountain ranges. The Ladakhi people live between 3,000 and 4,000 metres elevation. I spent five months working with a remarkable organisation called the Students Educational and Cultural Movement of Ladakh (SECMOL). Among the excellent work done by SECMOL is passive solar design/build using rammed earth.
Ladakh is a desert in the sky. Its primary resources are earth and sun. Trees are scarce. Wood is costly. Homes have been made using rammed earth for centuries, but better design has improved their performance during the last two decades. It is now possible to build homes, schools, and offices that are completely heated by sunshine. I spent a winter there in a room that was much warmer than most homes in the Manawatu.
Passive solar design is not only about sunshine. It also relies on thermal mass and insulation in proper proportions. Getting the balance right can result in warm, comfortable homes with very low running costs. And here is the best part: building a high performance passive solar home is cost comparable with building a typical New Zealand home.
Maybe rammed earth or a Saltbox is not your cup of tea. No worries. These are just examples of good passive solar design. There can be variations on the theme, but the theme does not change:
A-B-C, easy as 1-2-3, simple as solar gain, thermal mass and insulation. That’s how easy a cosy home can be.