50 psf of snow is Massachusetts. Not here.

S = C_b·Ss + Sr, with YOUR town’s Ss and Sr.

Nearly every timber-framing book in circulation is American. Their example frames are designed for 50 psf of snow — 2.39 kPa. That is western Massachusetts. Cape Cod is 25 psf; the Rockies, over 200.

In Quebec the load is calculated: S = C_b·Ss + Sr. S is the snow load the roof must carry, in kPa. Ss is the ground snow load that returns once in 50 years in your town; Sr, the rain load that adds to it, same return period. Both are read from appendix C of the 2020 NBC, in kPa. C_b is the roof factor, the share of the ground snow that stays on the roof: 0.55 — or 0.45 if your roof is 4.3 m wide or less, which covers many small buildings.

Taking 2.0 kPa as a default underestimates by 30 to 48 % as soon as you leave Montreal.

What it hits first: rafters and plates. No rafter, plate or tie-beam section from an American book carries over unchanged. The calculation has to be redone.

The designer asks WHERE you are building: it reads your town’s Ss and Sr from the code, applies the C_b for your roof, and sizes with that. If your town is not listed, you enter your own snow load.