Passive Solar Design

When we first started looking for property, we knew we wanted a lot with southern exposure. This Lillooet Lake lot faces due south, overlooking the lake. Even though the mountains across the lake are around 8,000 feet and this property is at 650 feet elevation, we still get winter solar gain (low sun angles) on the south windows due to the fact that we have a couple of kilometers of water in front of the house.

We have spectacular views so we have designed in lots of windows in the east, south and west. This creates some design challenge, which is why we used sun path charts to determine what the heat gains would be in both summer and winter months. The charts are available on computer programs and they basically track the path of the sun and how it will hit your windows. From these charts we know that in the summer the sun’s angle is very high, so based on this latitude, we can make our decisions. This property’s location is known for extremely hot summers, so with the design and considering the sun path charts, we chose a 10 foot overhang on the south side, a six foot overhang for the west side main floor windows, and a five foot walkway above the west basement windows. The idea is that an overhang will shade the window in the summertime and reject the sun’s impact, while in the winter the low sun will hit the glass and come through to add to the energy gain in the house.

On the west side only, in addition to the overhangs we are also planning to use windows which incorporate high performance sun block glass, because the late afternoon sun will still make contact with the glass and add to the cooling load. In the winter, this location has a lot of sun hours, so based on the sun path charts and the design of our overhangs and the type of glass used, we know that we will be getting maximum passive solar gain on our south windows.