The Windbreak
This pattern is shaped by
Problem
When a site lies open to prevailing winter winds, two forces collide: the desire to use outdoor space year-round, and the physical reality that wind steals heat from bodies and buildings alike. A sunny January afternoon at -15°C can feel tolerable in still air, but the same temperature with a 20 km/h wind produces a wind chill of -24°C — the difference between a short walk and frostbite. Inside the building, infiltration through every crack and thermal bridging across every surface accelerates; the furnace runs and runs. The site that ignores wind pays for it in heating bills, in frozen faces, and in outdoor spaces abandoned from November to March.
Evidence and Discussion
Wind chill is not metaphor. Environment Canada's wind chill index calculates that exposed skin freezes in 10-30 minutes at -25°C wind chill, but can remain outdoors far longer in calm conditions at the same temperature. In Edmonton, prevailing winter winds come from the northwest, averaging 12-15 km/h in January, with gusts frequently exceeding 40 km/h. The Prairie Farm Rehabilitation Administration (PFRA), working across the Canadian prairies from 1935 onward, established that properly designed shelterbelts reduce wind speed by 50-80% for a distance of 10-15 times the windbreak's height on the leeward side. A row of spruce 8 meters tall protects a zone 80-120 meters deep.
The heating implications are substantial. Natural Resources Canada's EnerGuide program identifies air infiltration as responsible for 25-40% of heating energy loss in Canadian homes. Every 1 km/h reduction in wind speed at the building envelope reduces infiltration proportionally. The USDA's National Agroforestry Center, drawing on decades of shelterbelt research, documents that farm buildings protected by windbreaks use 10-25% less heating fuel than exposed structures. In urban contexts, the effect compounds: wind blocked at the neighborhood scale reduces the load on every building within the protected zone.
Alexander's pattern 105, South Facing Outdoors, addresses solar orientation but assumes a temperate climate where wind is secondary. At 53°N, the winter sun hangs so low — less than 15 degrees above the horizon at the solstice — that solar gain through vertical surfaces matters more than it does farther south. But that low-angle sun is easily blocked by wind protection on the wrong side. The windbreak must be placed to block northwest winds while preserving the southern sky. This is geometry, not preference: conifers to the north and west, deciduous or open structure to the south. The Finnish standard for outdoor comfort (the PET, or Physiologically Equivalent Temperature index) confirms that wind reduction has a larger effect on perceived warmth than solar gain at temperatures below -10°C.
Shelterbelts need not be forest-scale. The City of Spruce Grove, west of Edmonton, requires developers to plant coniferous windbreaks along the north and west edges of new subdivisions — typically a double row of white spruce or Scots pine at 3-meter spacing. After fifteen years, these windbreaks are effective. Where mature trees are absent, earth berms perform the same function immediately: a berm 2 meters high blocks wind as effectively as a young tree row, and faster. The best windbreaks combine both: a berm planted with conifers gains height over time.
Therefore
on every exposed site, place a windbreak to the north and northwest — conifers, earth berms, or solid structures — at a distance no greater than ten times the windbreak's height from the spaces you wish to protect. Size the windbreak to reach at least 6 meters in height at maturity, or build a berm of at least 2 meters. Leave the south and southeast open to low winter sun. Test: stand in the protected zone on a windy January day. If you can feel the wind cut, the windbreak is too far, too sparse, or too low.