Set a joist cantilever over dropped beams

Use a cantilever to solve a layout problem

A designed joist overhang can let the finished deck edge extend beyond the outer dropped beam. That can recess the support line or help coordinate the edge with the space below. It does not remove the need for support; it changes how the joist delivers load back to the beam and the supported part of the joist.

A short backspan, unusual loading or a guard connection at the edge can make an apparently modest overhang unsuitable. Choose an overhang because it helps the job, then verify the complete design. A beam extending beyond its end post is a separate cantilever and must not borrow a joist limit.

Separate joist overhang from beam overhang

A joist cantilever is the joist extending past its last support. A beam can also extend past its end post; that is a different member and a different check. The Joist cantilever control adjusts the former.

The control applies to dropped beams, where the joists continue over the beam. Flush beams stop the joists at their faces and are not moved by this setting.

Read the selected limits

The current guide profile uses the City of Peterborough’s published residential-deck guidance: 400 mm for 2×8 joists and 600 mm for 2×10 or larger. The guide is an aid to the Ontario Building Code, not a substitute for the full requirements or a local project review.

The UC planner also limits each overhang to one third of its adjacent clear backspan. That is expressed as 3:1 backspan to cantilever. It is an additional planner restriction, not a claim that 3:1 is a universal Ontario code rule.

Selected maximum = smaller of:
• the joist-size guide cap
• adjacent clear backspan ÷ 3

Use the actual support faces

The overhang is measured along each joist from the beam’s outside face to the joist end. Backspan is the clear distance from that beam’s inside face to the next supporting beam or ledger face. Beam width is not included in either clear distance.

For example, a 900 mm clear backspan gives a 300 mm ratio limit. With 2×8 joists, that is below the 400 mm guide cap, so the selected maximum is 300 mm. This example only demonstrates the app’s length check.

The app stores the metric caps exactly. Imperial Use maximum rounds downward to a sixteenth of an inch, so it does not treat the approximate 16-inch or 24-inch labels as exact metric limits.

Apply the overhang and inspect the result

• In Framing, enter a covered joist size and enable Limit cantilevers over dropped beams.
• Enter Requested joist overhang and choose Apply cantilever, or choose Use maximum.
• Eligible perimeter dropped beams move to suit the request; short returns and short backspans can reduce it.
• Read the current status and the Dropped-beam joist cantilevers table. Review any skipped beams or unverified ends.
• Reapply after changing supports or the outline. Manual edits are checked but do not silently reposition other beams.

Understand the scope of a passing length check

Within selected limits means those measured lengths meet this guide profile and its ratio check. It does not verify loads, species, grade, joist or beam capacity, bearing, connections, guards, footings or the complete code requirements.

A supported backspan must exist before the ratio can be checked. Beam overhang beyond a post is reported separately in the framing schedule and is not capped by this control. Use the project’s applicable requirements for both member types.

Review beam paths, supports and framing schedules