Garage Plans : Roof Trusses Or Rafters - Do You Know The Difference?

WILLIAMSBURG, Va. - Feb. 6, 2014 - PRLog -- Behm Design offers both truss and rafter design garages plans.

Roof trusses are the predominant industry standard method for building roofs, due to their economy and versatility in possible roof shapes. Usually, roof trusses are used when the span or width of a garage exceeds 20 ft. (for lesser widths rafters are more economical)

A roof truss is a load carrying, spanning member made of wood components (usually 2x material), connected together with metal plates, shear connectors, etc. Used together with other trusses, usually spaced at 24" on centers, the roof loads are carried out to the walls efficiently. Trusses are designed as a package, fabricated according to state laws and engineered as part of their manufacture. ("engineering" means that loads applied to the trusses and resulting stresses in the materials are analyzed and components sized to carry the required loads for the specific span and truss shape. This is typically done under the supervision of a state-licensed engineer or architect.) As this is an industry wide accepted practice, it is not necessary to to have the drawings for the garage stamped by an engineer. The roof system is treated as a distinct, pre-engineered component of the whole building structure and engineer stamped/signed documentation usually comes with the truss package.

Trusses are almost unlimited in possibilities for shape. Attic storage, gambrel, and attic loft truss profiles are becoming popular due to the economy of structure.
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Rafters with Ceiling Joists are often used for smaller garage roof spans or widths, typically less than 20 ft, due to greater economy. The rafter spans from the bearing wall to the ridge board at the roof peak and is sized with tables in the building code for span, spacing, load, slope, wood species and grade. The continuous ridge board secures the roof peak assembly. The ceiling joist acts as a tension tie to keep the rafters from splaying out under load and creates a ceiling surface. This roof framing assembly is typically spaced at 16" o.c. or 24" o.c, is completely prescriptive in the code and so usually requires no engineering.

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The garage plans provided by Behm Design typically include a roof framing (layout) plan and cross-section view which illustrate either the roof framing or the recommended truss profile (which serves only as a basis for the truss engineering and manufacture by the supplier/fabricator) Usually, when ordering trusses through your materials supplier or setting up your project with your builder,you can request adjustments to the profile shown (to match and existing house, for example)

It's advisable to check with your local building dept. BEFORE modifying the plans, as some do not allow it.

Visit Behm Design to see over 300 garage plans currently available.