Construction Purlin Flat Roof

Purlin plates are beams which support the mid span of rafters and are supported by posts.

Construction purlin flat roof.

Metal roof purlins are installed horizontally under metal roofs. The common 4 on center design is suitable for snow loads up to 60 for most applications. Also known as sheeting rails purlins create the roofing members of the secondary framing of a steel building. They are installed on top of the roof rafters with a felt underlayment or vapor barrier installed on top.

Purlin plates in wooden construction. Purlins are 2 by 4 feet and are installed much like metal roofing. Roof live load roof dead load x spacing x span of purlin 2. Purlins are an important component in a pre engineered steel structural kit.

By supporting the rafters they allow longer spans than the rafters alone. 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. Metal building roof purlins provide three structural functions. 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.

The term plate means a major horizontal supporting timber. A purlin plate in wood construction is also called an arcade plate in european english under purlin and principal purlin. They give added support to the roof and also provide a nailing surface for the end panels and drip edge. These structural supports run perpendicular across the rafter beams.