Build season
The slab-on-grade is poured during the 6-week factory build. Outside the comfortable window, a pour can still go ahead with cold-weather protection, at extra cost. A slab is never placed on frozen ground.
| Region | Last spring frost | First fall frost | Comfortable pour window | Frost depth | Order by |
|---|---|---|---|---|---|
| Ottawa / Gatineau | May 9 | Oct 12 | mid-May → mid-Oct | ~1.5 m | Aug 24 |
| GTA (Toronto) | Apr 20 | Nov 1 | late Apr → end Oct | ~1.2 m | Sep 13 |
| GTA west (Mississauga / Hamilton) | Apr 20–25 | Oct 28 | late Apr → late Oct | ~1.2 m | Sep 9 |
| London | Apr 22 | Oct 18 | late Apr → mid-Oct | ~1.2 m | Aug 30 |
| Windsor | Apr 20 | Oct 28 | late Apr → late Oct | ~1.2 m | Sep 9 |
| Barrie | May 21 | Sep 24 | late May → late Sep | ~1.5 m | Aug 6 |
| Sudbury | May 31 | Sep 17 | June → mid-Sep | ~1.8 m | Jul 30 |
| Montréal | May 9 | Oct 7 | mid-May → early Oct | ~1.2–1.5 m | Aug 19 |
| Québec City | May 17 | Sep 28 | late May → late Sep | ~1.6 m | Aug 10 |
Frost dates are ECCC 1991–2020 normals (50th percentile) via GrowersGuide. Frost depths are secondary sources: confirm them with the building department. The comfortable window is our heuristic, between average last and first frost, not a code limit. Order-by dates are the first-frost date minus 7 weeks. In practice, apply for permits in spring.