Spray Foam Insulation in Carstairs, AB.

81% of Carstairs dwellings are single-detached, one of the highest shares of the 27, and the ledger records an 86.4% homeownership rate. Owner-occupied detached houses, mostly built since 1980.

That combination produces a particular pattern of complaint. The building envelope is broadly sound, so the failures that get noticed are localised and comparative — one room colder than the rest, a floor over the garage that never warms up, an ice dam on one roof plane and not the others. Those all point at discontinuities rather than at a missing insulation layer: a bonus room over an unheated garage, a cantilever above outside air, a rim joist above an unfinished basement, an attic hatch in a heated ceiling. In an owner-occupied house the person who notices is also the person who can authorise the fix, which is not true everywhere in this region.

Carstairs is assigned RED DEER REGIONAL A (climate ID 3025480) from about 85 km north — 5,619 heating degree days at an 18 °C base, an average January daily minimum of -17.6 °C, -43.8 °C at the extreme.

That is a long borrow, and it likely overstates the heating load here: Carstairs sits between Red Deer and Calgary, and the Calgary station reads 4,994 degree days — several hundred fewer. The ledger does not interpolate between stations, so the northern figure stands, with the caveat attached.