Back to all deflection criteria
SpanMan calculates joist deflection criteria in the following way:
- From the building type determine whether the joist is in a residential or commercial building type.
- Start with the appropriate deflection criteria below.
- Find the most brittle load the member is supporting.
- Increase the span ratio deflection criteria based on the load's brittleness.
Residential deflection criteria for Joists
| Span Maximum (mm) | Span Ratio | Overhang Maximum (mm) | Overhang Ratio | |
| Dead Load | 15 | L / 300 | 6 | L / 150 |
| Live Load | 9 | L / 360 | 5 | L / 180 |
Commerical deflection criteria for Joists
| Span Maximum (mm) | Span Ratio | Overhang Maximum (mm) | Overhang Ratio | |
| Dead Load | 20 | L / 300 | 6 | L / 150 |
| Live Load | 25 | L / 300 | 5 | L / 180 |