Hoosir's Woodworking Diary

Basic Roof Trusses Design specifications for Better Construction

Approximately 75% of homes built today utilize pre-fabricated roof trusses in place of conventional roof rafters to support the roof! Roof trusses are pre-manufactured wood structures which are fabricated in a workshop and carefully designed to support the roof and the load on outside walls.

Ask most engineers today and they will confirm that engineered roof trusses are the only option and are much superior compared to the old roof frames. The major advantage of using pre-fabricated roof trusses are speedy construction and significant cost savings.

In designing roof trusses, the following aspects should be carefully considered:
# Fraction of all parts of a joint so that the maximum strength can be achieved throughout
# Provide adequate bearing surface to get the compression on the surface well within the safe limits
# Spread bolts and rivets so as to provide the greatest resistance with the least cutting away of remaining structural members
# Observe that the central axis of each component coincides as much as possible with the line of action of the stress
# Examine all members and assemblies for compressive, tensile, transverse and shear forces.

It is very critical that you state correct type, measurements and other details when placing an order for roof trusses. General mistakes include incorrect specifications and less attention to the design aspects of roof trusses before fabrication.

Basic specifications needed when ordering roof trusses for your home or structure include:
# Truss Type
# Truss Span (Length of the bottom chord)
# Number of Trusses
# Truss Bearing Width
# Design Load (Live, wind, dead and other loads to which the trusses are subjected)
# Overhang Length (Space between the bottom edges of the top and bottom chords)
# End Cut (square or plumb cut)
# Heel Height (Space between the top of the top chord and the bottom of the bottom chord)
# Roof Slope, etc

For any queries related to Roof Truss design and related design drawings email us at info@outsourcestructuraldrafting.com

Visit us at http://www.outsourcestructuraldrafting.com/services.php for more information.

About the Author

Richard Bose is structural draftsman at OSD – an India based Structural Engineering firm offering full services such as structural steel analysis, structural drafting, shop drawings and structural design services at affordable rates. Email us at info@outsourcestructuraldrafting.com

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