Construction Purlin Flat Roof

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

Construction purlin flat roof.

A purlin plate in wood construction is also called an arcade plate in european english under purlin and principal purlin. The common 4 on center design is suitable for snow loads up to 60 for most applications. Or less x 1 1 cfu the flat use factor for applying the load to the wide face of a member. The higher the snow load the closer the purlin spacing required.

Also known as sheeting rails purlins create the roofing members of the secondary framing of a steel building. Metal roof purlins are installed horizontally under metal roofs. By supporting the rafters they allow longer spans than the rafters alone. Purlins are 2 by 4 feet and are installed much like metal roofing.

Purlin plates in wooden construction. Purlins are an important component in a pre engineered steel structural kit. 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. 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.

The term plate means a major horizontal supporting timber. They are installed on top of the roof rafters with a felt underlayment or vapor barrier installed on top. Roof live load roof dead load x spacing x span of purlin 2. Metal building roof purlins provide three structural functions.