Spray Foam Insulation in Sundre, AB.

Read the two shares together. 38.8% pre-1980 is a middling figure for this region, but it lands on a stock that is only 50.6% detached — so a large share of Sundre's older dwellings are something other than a house on a lot. StatCan's structural-type categories cover duplexes, row units, apartments and movable dwellings; the ledger records the detached share but does not break down the remainder.

What the non-detached categories have in common is that adding depth on top of a ceiling does not solve them. Attached units share air paths through party walls and common attic space, so heat lost from one suite surfaces in another. Where the stock includes movable dwellings, the floor assembly sits over a skirted and often vented crawl space, with the plumbing in the same cold cavity. In both cases the result turns on whether the air barrier is continuous around the individual unit.

Sundre's assigned station is RED DEER REGIONAL A (climate ID 3025480), about 98 km away — 5,619 heating degree days at an 18 °C base, a -17.6 °C average January daily minimum, -43.8 °C at the extreme.

One local note the borrowed figure cannot capture: Sundre is separately described as having one of the highest average diurnal — day-to-night — temperature variations in Canada, particularly in winter (Wikipedia). That is a qualitative characterisation and no figure is on record for it, so it is not quantified here. But a large daily swing loads an envelope differently from a steady cold: the assembly expands and contracts every day, and any part of it that is alternately warm and cold sees repeated condensation cycles rather than one long freeze. Annual heating degree days say nothing about that.