Construction Purlin Flat Roof

Metal roof purlins are installed horizontally under metal roofs.

Construction purlin flat roof.

The common 4 on center design is suitable for snow loads up to 60 for most applications. 8 x section modulus of a 4 2 of 1 3125 x fb fiberstress in bending x 1 15 duration of load x 1 15 cr repetitive member factor as the purlins are spaced 24 o c. Also known as sheeting rails purlins create the roofing members of the secondary framing of a steel building. The term plate means a major horizontal supporting timber.

Too high a snow load means the purlins fail regardless of how close together you put them because a 2 4 or 2 6 flat can only span a certain distance between trusses as snow loads increase. Roof live load roof dead load x spacing x span of purlin 2. A purlin plate in wood construction is also called an arcade plate in european english under purlin and principal purlin. Purlin plates are beams which support the mid span of rafters and are supported by posts.

Or less x 1 1 cfu the flat use factor for applying the load to the wide face of a member. Purlins are 2 by 4 feet and are installed much like metal roofing. They are installed on top of the roof rafters with a felt underlayment or vapor barrier installed on top. By supporting the rafters they allow longer spans than the rafters alone.

Metal building roof purlins provide three structural functions. The higher the snow load the closer the purlin spacing required. Purlins are an important component in a pre engineered steel structural kit. They give added support to the roof and also provide a nailing surface for the end panels and drip edge.