Roof Deck Weight Limit

Design

• According to the Steel Deck Institute, the design of buildings using steel decking material should meet standards determined by the North American Specification for the Design of Cold-Formed Steel Structural Members. The SDI notes that the combined dead and live design loads shall not exceed 60 percent of the strength yield with a maximum strength yield of 36 kilograms per square inch, or 36 ksi.

Stress Deflection

• The design of a roofing structure with roof decking requires that the designer take into account stress deflection, or the way in which the load of the roof is spread out based on the roof's design. According to SDI, the deflection must not be more than 1/240 of the roof's span or 1 inch, whichever is less. Stress deflection must be calculated on the basis of the measurement from centerline to centerline. The designer must calculate and determine whether supplemental supports are needed. Suspended loads such as hanging ceilings and light fixtures must also be included in the calculation.

Construction Loads

• Construction loads must be taken into account when calculating the weight limit of metal roof decking. These loads are any of the weight used in the construction process, which can include workers and building materials. The deck must be designed in such a way that it provides at least 30 lbs. of construction load per square foot. If it appears that the load will exceed this 30-lb. load limit, the designer is required to either decrease the span of the roof decking or increase the thickness of the decking.

How It Works

• Roof deck is specifically designed to distribute loads into the building frame that supports the material. The Steel Deck Institute notes that steel roof decking is not meant to be used in conjunction with other materials. The rib openings in roof decking are typically narrower than those found in metal floor decking. These narrow ribs help support the greater load of the roofing structure. Roof deck panels are painted with a special galvanized paint designed to strengthen the metal itself.