Roof Truss Depth To Span Ratio

Most economical when the difference in slope between the top and bottom chords is at least 3 12 or the bottom chord pitch is no more than half the top chord pitch.

Roof truss depth to span ratio.

Maximum span to depth ratio of 20 max. Estimate of depth 1 for every foot of span. Cantilever is of the total span max. For flat trusses a minimum depth to span ratio between 1 8 and 1 10 is recommended the deeper trusses being preferred for the longer spans.

Typically roof live load is snow while floor live loads are furniture human occupancy storage. Cantilever with concentrated load at the end of the cantilever is 2 times the depth of the truss. Roofs should have a minimum slope of in. Live loadany temporary applied load to a floor truss chord.

The span to depth ratio of trusses ranges from 10 to 25 depending on the intensity of the applied load. Add 6 for roof trusses and 4 for floor trusses to your answer. The lower the ratio the longer are the shear members in the truss and the larger is the volume occupied by the roof structure. Flat the most economical flat truss for a roof is provided when the depth of the truss in inches is approximately equal to 7 of the span in inches.

For efficient structural performance the ratio of span to truss depth should be chosen in the range 10 to 15. You will be able to decrease the depth if the truss company has higher grade lumber for the roof and floor trusses or uses double chords for the floor trusses. This will get you a starting depth for a basic truss. Representative floor truss tables.

Floor trusses rules of thumb. L d ratiothe ratio of the truss span l to its depth d both dimensions in inches. Per ft for proper drainage although steeper slopes are often desirable. The load span tables shown below demonstrate only a tiny subset of the possible combinations available with trussteel cfs roof trusses.