Load rules for a deck serving one Ottawa home?

The 2024 Ontario Building Code sets two main load rules for a deck serving a single dwelling unit. First, the deck structure must be designed for the specified roof snow load for the site or 1.9 kPa, whichever is greater. Second, deflection of deck beams, joists and decking is limited to 1/240 of the span.

Those two figures cover the deck surface and its framing. Guards have their own load requirements. The 2024 Ontario Building Code, Table 9.8.8.2, sets exterior guard loads for a deck serving not more than two dwelling units at a top load of 0.5 kN per metre, or a concentrated load of 1.0 kN applied at any point, and a vertical load of 1.5 kN per metre. Ontario deems guards built to MMAH Supplementary Standard SB-7 to meet the load requirement. Stairs serving not more than one dwelling unit are designed for 1.9 kPa.

A few situations push the design beyond Part 9 of the Code. The 2024 Ontario Building Code section 9.17.1.1(1)(b) limits the Part 9 column rules to beams carrying loads from not more than two levels of wood-frame decks where the supported joist length does not exceed 5 m and the combined snow and occupancy load does not exceed 4.8 kPa. Beyond those limits, Part 4 engineered design applies. A hot tub is one case to raise early: nothing in Part 9 sizes a deck for a filled hot tub, and we found no Code figure for that load. If a hot tub is part of the plan, the deck needs a design that accounts for it, and confirming the approach with the City's Building Code Services and an engineer before purchasing is worth doing.

The snow load in that rule is the specified roof snow load for the site; the designer or engineer on the permit drawings applies it.

On the permit side, the City of Ottawa requires scaled, fully dimensioned drawings that show joists, beams, posts and decking with size, spacing, direction and span. The drawings must also show the deck-to-house connection where the deck is attached. The designer or engineer sizes those members for the loads above.

One thing worth asking any builder before signing: can you show me how the deck framing and guard posts will be sized to meet the load requirements, and who is taking design responsibility on the Schedule 1 for the permit application.