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Community and Q&A

Sizing timber frame roof purlins

johnharry | Posted in General Questions on

For those of you that live in a moderate snowy area such as Pennsylvania or New York and have a Timber Frame roof system of bents and purlins with t&g on top of purlins. Question is with bents on 16′ centers what size purlins do you have? I imagine to satisfy the code it would be considered rafters with ceiling attached which would fall under the 240 deflection rule. For purlins on 48″ centers, 15′ length at 30psf (1800 lbs) a 5X7 would have .799 deflection, a bit above the allowable .75. This is telling me it would require a 6X8. Make sense? What size bents do you have holding up your purlins?

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  1. GBA Editor
    Martin Holladay | | #1

    This type of question needs to be answered by an engineer.

    If you are ordering your timber frame from a timber-frame company, the company should have an engineer on staff. If you are designing and building your own timber-frame house, it's time to hire an engineer.

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