purlins, 2o12

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david ayers
david ayers's picture
purlins, 2o12

The New Features 2012 list at Softplan.com, under item "Roof" mentions the ability to include purlins. However, the pic with it that is supposed to show these purlins shows instead what I call lath. I little investigation reveals that there are others who also regard as purlins what I call lath. And others who use the same nomenclature I do. Anyway, it caused me to wonder what are the editables for Softplan 2012's purlin /lath. Can there be more than one set in a roof? Say, one set set to be under-the-rafters support purlin, and the other lath? If anybody knows, much appreciated.

David Ayers

Bill Wimberley
Bill Wimberley's picture

The term 'purlins' appears to be more of a generic term rather than a specific term. Essentially, it is a structural member that runs perpendicular to the rafters. There are under purlins that go under the rafters to give them support. Another type of purlin is typically used in commercial steel buildings or timber frame roofs to provide structural members between the main roof rafters. This type would be typically flush with the tops of the rafters.

SoftPlan provides what are sometimes referred to as over purlins. Depending on how you configure the lumber size and spacing these would typically be used in place of solid sheathing for applications such as metal roofing, cedar shakes, and tile roofing. And I am agreement with you. I have always referred to this as lath. But because you can make the lumber and spacing to be any size then I believe that purlin is the proper term. Since the members do run perpendicular to the rafters it satisfies the definition of a purlin.

Bill is the owner and maintainer of SoftPlanTuts.com