Roof Poding Deflection Limit

Serviceability states and deflection criteria which includes guidance on installation tolerances for purlins and rails supporting profile metal roof sheeting and wall cladding and examines structure positioning from the point of view of the practicalities of installing a roof or wall covering.

Roof poding deflection limit.

See the table below. If that same joist had gypsum ceiling l 240 the allowable deflection is 0 6. The most effective method to minimize the effects of ponding is to increase the recommended minimum design slope to 1 2 in 12 for roof applications and 3 8 in 12 slope for floor applications. On a roof with a slope greater than 4 to 12 the live load limit is typically adjusted downward from 20 psf to 15 psf to allow for the relatively greater dead load on the steeper roof.

Understanding the causes of flat roof ponding. The document can be downloaded from the mcrma web. Note it gives the allowable deflection based on a fractional span quantity so a larger denominator will yield less deflection. Ponding is the phenomenon of water that remains standing on a flat roof for more than 48 hours since the last rainfall.

This limit is not intended to safeguard against ponding. Adhered roof insulation and single ply membranes often are more. Any non structural partition under the beam must be able to accommodate this deflection. Load deflection limit of l 120 for a roof deck whereas ibc 2015 table 1604 3 footnote a stipulates a total load deflection limit of l 60 for structural metal roofing.

The total load deflection limit is l 180 and l 480 for the roof and floor respectively. The severity of ponding water should never be underestimated as it will ultimately result in structural deformations water leaks and other problems. M va z qˆ 2 2 0 π a 8 this bending moment m0 corresponds very well with the bending moment as a result of a uniformly distributed load q since. Depending on how the roof insulation and roof membrane are attached single ply membrane roof manufacturers also may have minimum requirements for roof deck properties.

For example a floor girder spanning 36 ft may deflect up to 1 2 inches under a live load only deflection limit of l 360. 7 752 8 4 ˆ 2 2 2 2 2 2 0 a a qa qa m q π π π 9 the first order deflection in the middle of the beam δˆ0 can be determined by considering.