Roof Truss Depth To Span Ratio

The span to depth ratio of trusses ranges from 10 to 25 depending on the intensity of the applied load.

Roof truss depth to span ratio.

The architectural design of the building determines its external geometry and governs the slope s given to the top chord of the truss. Representative floor truss tables. Floor trusses rules of thumb. 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.

Typically roof live load is snow while floor live loads are furniture human occupancy storage. Per ft for proper drainage although steeper slopes are often desirable. Roofs should have a minimum slope of in. Add 6 for roof trusses and 4 for floor trusses to your answer.

L d ratiothe ratio of the truss span l to its depth d both dimensions in inches. 05425 cold formed steel trusses roof truss spans every trussteel roof truss is a custom design based upon the unique load span bearing use and code criteria of a particular project. The load span tables shown below demonstrate only a tiny subset of the possible combinations available with trussteel cfs roof trusses. 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.

The lower the ratio the longer are the shear members in the truss and the larger is the volume occupied by the roof structure. Cantilever without a concentrated load at the end is 4 times the depth of the truss max. Live loadany temporary applied load to a floor truss chord. 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.

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. For efficient structural performance the ratio of span to truss depth should be chosen in the range 10 to 15. Cantilever with concentrated load at the end of the cantilever is 2 times the depth of the truss. This will get you a starting depth for a basic truss.