A low door threshold makes shallow framing tempting. Then someone says, "Just use 2x6s." The useful follow-up is: how far will they span, and what will support them?
Three measurements that sound interchangeable
| Measurement | What it describes |
|---|---|
| Joist depth | The size of the structural member, such as nominal 2x6. |
| Joist span | The distance the joist carries between supports. |
| Joist spacing | The distance from the centre of one joist to the next. |
A twelve-foot-long deck does not automatically have a twelve-foot joist span. An intermediate beam can change that. Conversely, placing joists closer together does not make every long span acceptable.
What the local example establishes
Oakville's sample drawings, sheet A-5, include 2x6 joists in a span table. So a blanket claim that Ontario never allows them is unhelpful. The same table distinguishes joist spacing and cantilever conditions.
The sample is an application aid, not a design approval for your property. Have the designer confirm the applicable lumber species and grade, loading, bearing, and current requirements rather than copying an isolated number from the drawing.
Shallow framing comes with a layout decision
On a low back-door deck, we drew both a deeper-joist option and a shallower frame with another support line. The shallow version helped at the threshold, but its extra beam competed with the ground clearance underneath. We checked the whole vertical stack on the drawing: finished board, joist, beam, and grade. Saving depth in one piece of wood wasn't enough if the next piece no longer fitted.
That is the comparison to price: two complete framing arrangements, including excavation and access to the connections. Ask how the framing will be assembled and inspected before the surface goes on. A cheaper piece of lumber is not necessarily a cheaper deck, especially when every later repair would have to come from above.
Get these details onto one drawing
- Actual support locations and joist spans, with any overhang shown separately.
- Joist size, spacing, species and grade, plus the decking product and direction.
- Any roof, hot tub, or other special load the designer must account for.
- Finished deck height and the route water will take away from the doorway.
Oakville's deck application guidance asks for structural and site information together. That is sensible: the joist choice, footing layout, and finished height belong to the same decision.