Barn Roof Framing Consideration

[ken]

**Barn Roof Framing Consideration
**8/13/06

How can we design a barn roof framing system to meet a minimum roof snow load requirement (ex. 30 psf)?

-Most roof framing system used is very "light" and you know why
-Purlin joist spacing?
-Rafter spacing
-Wind design requirement (uplift, etc.)
-How about the connectors
-Others (?)

[ken]

by Bruce Pooley » Tue Aug 15, 2006 8:07 pm

In this example, I think the material used for the roof sheathing/roofing is the key element. In this case, a light gauge corrugated metal panel has been installed. What fasteners and fastener spacings are required to create the roof diaphragm?

It is also interesting to see the purlins installed in the "plank" orientation over the top of the rafters. In many installations, the purlins are installed between rafters and flush with the top of the rafters. This allows fastening the metal panels to the rafters as well as the purlins. Fastening the metal panelsdirectly to the top of the rafters provides full lateral support of the rafter and thus increases the bending capacity of the rafter.

What other key elements are involved in this design?

[ken]

by ken » Wed Aug 16, 2006 4:33 pm

Well thought in the design conecpt and process.

The roof diaphragm is the key in designing a "light" roof framing system especially this structure.

The project requirement was to convert the existing barn structure to meet the current IRC code requirements. (i.e. the wind load design criteria and the local roof snow load requirements)

The connections and the building shapes play the important roles in using this light-framing approach.

Other design consideration will be the "uplift" check, bracing system requirements and the "ponding" check (for flat roof) for this light-framed barn structure. -Ken