Deck beam sizes on Ottawa permit drawings: who decides?

The beam size on a permit drawing is decided by the designer or engineer named on Schedule 1 of the permit application, not by the City and not by the builder on site. The City of Ottawa requires a complete set of scaled, fully dimensioned drawings, and those drawings must show every beam with its size, spacing, direction and span before the application is accepted.

Who takes design responsibility depends on what the homeowner puts on Schedule 1. The 2024 Ontario Building Code allows a homeowner to take design responsibility for drawings related to construction or alteration of a house they own, so a homeowner who is comfortable with the calculations may sign Schedule 1 themselves. If they name a BCIN designer instead, that designer sizes the beams. Where the deck falls outside Part 9 scope, for example where a post carries loads from more than two levels of wood-frame decks or the supported joist length exceeds 5 m or the combined snow and occupancy load exceeds 4.8 kPa, the design must follow Part 4 of the Code, which means an engineered design. The same applies where the foundation is on filled ground, peat or sensitive clay such as Leda clay: those conditions also require a design in conformance with Section 4.2 of the Code.

The beam size itself flows from the load the deck must carry. The 2024 Ontario Building Code sets the design load for a deck serving a single dwelling unit at the specified roof snow load or 1.9 kPa, whichever is greater, and sets a deflection limit of 1/240 for beams, joists and decking. The designer works from those numbers, the joist span, the beam span and the species and grade of lumber, to arrive at the beam dimensions. The City does not publish a table of acceptable beam sizes: it reviews what the drawings show and checks that the drawings are complete and dimensioned.

A few things worth knowing before the drawings go in:

• The framing plan the City asks for must show footing or foundation type, size and location; joist, beam, post and decking sizes, spacing, direction and span; and the deck-to-house connection if the deck is attached.
• Where helical piles are used, the City asks for a pile layout and specifications as part of the same drawing set.
• The permit fee is $12.75 per $1,000 of assessed valuation of the work, with a minimum of $117.00, and the application goes through the My ServiceOttawa portal with payment at the time of submission.
• The City lists a first review of 5 business days.

If the deck's walking surface will be more than 600 mm (24 in.) above adjacent grade and it is attached to or adjacent to the house, a building permit is required before any work starts. If it is a freestanding deck, a permit is required only if it is also greater than 10 square metres (approximately 108 square feet) in area and more than 600 mm above grade. Either way, no beam size is final until it appears on drawings that have cleared the City's review.

The most useful question to put to any designer or engineer before engaging them: ask them to walk you through how they will size the beams given your deck's span, load and soil conditions, so you understand what is driving the numbers on the drawings.