Passive Home Heating: Winter Sun (4 min read)

You can tell the time of the year in a passive solar home by where the light falls into the home (or not) on a sunny day. As the winter solstice approaches, the sun falls into the back of the home, until on the day of the solstice, I designed for it to reach the very back wall of my home.

You can see in the photo here, taken a few weeks ago in the late fall how the sunlight is streaming onto the thermal mass earthen floor, heating the mass. I like living my life close to the planet, connected to its patterns. Its the way humans have lived for thousands of years, like my ancestors in the British isles, the ancient pueblo cultures of the American southwest and multiple other places around the world – we know they lived with this awareness because they built their homes and other structures to mark solstices and to take advantage of this resource that is freely offered by our sun and the positioning of our planet.

Passive solar design and orientation of a home doesn’t provide all of its heat in my climate at 50 degrees north here in southern BC, Canada, but it does provide a considerable portion. Most of the rest of my heat is provided by a deep foundation thermal storage system connected to the active solar heating panels mounted on the roof. The engineer’s calculations estimated that the wood I use for top-up winter heat would be needed for only about 20% of the home’s heat. To put that into perspective, most conventional homes in the area use about a pickup truck’s worth of wood per month, for about 6 months of the year. I so far have used only 2 pickup truck loads per year. I also typically start burning wood a month later in the fall than my neighbours and stop burning a month earlier than them in the spring. (Note: Ideally the home’s top-up heat would be electric, but because I live rurally, use such a small amount of wood, have a good local supply of standing deadwood for wood and the grid here is often down, I chose wood combustion for this home).

Similarly, passive solar design provides a proportion of cooling in the opposite time of the year. As summer progresses, the wide eaves on the home shade and keep the sun from entering. Carefully placed efficient windows yield light but not heat in the summer months. The thickly insulated straw bale walls provide insulation. Along with careful manual window opening and closing, efficient windows, carefully sized and placed provide low-tech, simple temperature control. The house is cooled at night with outdoor air by opening windows sited to gather the almost-always-present valley winds and closing them at day to prevent heat gain. This is all that is required to keep the home cool, even in the traditionally hot summers of this semi-arid region of BC where days can sometimes reach up to 40C.

Why aren’t more homes built this way? Well, that’s why I am writing this, hoping to increase awareness. We also need both land use planning and building code improvements based on local and regional resources, to encourage and require it. The BC Step code is ‘stepping’ in the right direction. But much more could be done. In urban areas, land use planning could take into better account access to the solar resource, both for passive design and for solar electricity access, things that future community designs will ideally be planned around, creating better access for all buildings.

Land use plans need to strategically take advantage of local topography, so that buildings (and food gardens) can access the sun. Buildings need to be able to align their axis east-west as needed and be protected from shading by adjacent structures. We can use east and west slope roofs to gather the solar resource for electricity and heat, but significantly more is gained from direct south exposure. East and West windows require planning to mitigate potential overheating. Ideally all structures built now and in future should have their alignment designed to take full advantage of this resource, for electricity and heating and also for home comfort and light. These things, along with efficient design strategies and materials, can make our building stock part of the many solutions for Climate Change.~