Back to all deflection criteria
SpanMan calculates rafter deflection criteria in the following way:
- From the building type determine whether the rafter 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 Rafters
| Span Maximum (mm) | Span Ratio | Overhang Maximum (mm) | Overhang Ratio | |
| Dead Load | 12 | L / 300 | 10 | NA |
| Live Load | 20 | L / 250 | 10 | NA |
| Wind Load | 33 | L / 150 | 10 | NA |
Commerical deflection criteria for Rafters
| Span Maximum (mm) | Span Ratio | Overhang Maximum (mm) | Overhang Ratio | |
| Dead Load | 20 | L / 300 | 17 | NA |
| Live Load | 24 | L / 250 | 17 | NA |
| Wind Load | 40 | L / 150 | 17 | NA |