Construction Purlin Flat Roof

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.

Construction purlin flat roof.

Purlins are 2 by 4 feet and are installed much like metal roofing. Or less x 1 1 cfu the flat use factor for applying the load to the wide face of a member. Also known as sheeting rails purlins create the roofing members of the secondary framing of a steel building. By supporting the rafters they allow longer spans than the rafters alone.

They are installed on top of the roof rafters with a felt underlayment or vapor barrier installed on top. The term plate means a major horizontal supporting timber. They give added support to the roof and also provide a nailing surface for the end panels and drip edge. The common 4 on center design is suitable for snow loads up to 60 for most applications.

The purpose of purlins. A purlin plate in wood construction is also called an arcade plate in european english under purlin and principal purlin. Metal building roof purlins provide three structural functions. Metal roof purlins are installed horizontally under metal roofs.

Purlin plates are beams which support the mid span of rafters and are supported by posts. The higher the snow load the closer the purlin spacing required. 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.