Roof Design Loads

In commercial or industrial buildings for each floor or portion thereof designed for live loads exceeding 50 psf 2 40 kn m 2 such design live loads shall be conspicuously posted by the owner or the owner s authorized agent in that part of each story in which they apply using durable signs.

Roof design loads.

50 psf x 14ft 700 pounds per lineal foot. The amount of weight a truss needs to support per square foot is important. The north zone middle zone and the south zone are identified on the roof load zone map above. Live roof load w wind load s snow load e earthquake load r rainwater load or ice water load t effect of material temperature h hydraulic loads from soil f hydraulic loads from fluids.

The dead load on a roof is the weight of the roof structure itself along with any permanently attached materials or structures on the roof so it must be designed first of all to support itself. Loads used in design load equations are given letters by type. Depending on your region you may need to design for a maximum snow load of anything between zero to 65 pounds per square foot or roughly 0 3 kpa. 910 pounds per lineal foot.

For a larger map with greater detail refer to asce 7 98. Roof loads are a downward vertical force on the home. This downward imposed load on the home is also known as the snow load. A fixed node will provide support in both directions down the length of the roof truss members often called the x and y directions.

Where uniform roof live loads are reduced to less than 20 psf 0 96 kn m 2 in accordance with section 1607 12 2 1 and are applied to the design of structural members arranged so as to create continuity the reduced roof live load shall be applied to adjacent spans or to alternate spans whichever produces the most unfavorable load effect. This includes all of the roofing material and ceiling along with loading for construction purposes and then environmental factors such as wind and snow. D dead load l live load l. This means that one is a fixed node and the other is a rolling node.

Framing table for maximum roof rafter spans. Roof load live load design is affected by the shape of the roof whether it is flat curved or pitched. 15 psf x 14ft 210 pounds per lineal foot. Let s look at the sample table below which shows maximum rafter spans for a snow load of 31 3 pounds per square foot psf.

3 20 residential structural design guide. In order for a roof truss load to be stable you need to assign two of your nodes on each truss to be support nodes.