Roof Design Loads

Roof load live load design is affected by the shape of the roof whether it is flat curved or pitched.

Roof design loads.

The amount of weight a truss needs to support per square foot is important. 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 downward imposed load on the home is also known as the snow load. This includes all of the roofing material and ceiling along with loading for construction purposes and then environmental factors such as wind and snow.

15 psf x 14ft 210 pounds per lineal foot. D dead load l live load l. Chapter 3 design loads for residential buildings. In areas where the ground snow load is less than 15 psf the minimum roof live load refer to section 3 4 is usually the controlling rgavity load in roof design.

A fixed node will provide support in both directions down the length of the roof truss members often called the x and y directions. 50 psf x 14ft 700 pounds per lineal foot. Loads used in design load equations are given letters by type. It is important to list live load dead load and total load separately because live load is used to compute stiffness and total load is used to calculate strength.

910 pounds per lineal foot. 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. Framing table for maximum roof rafter spans. The north zone middle zone and the south zone are identified on the roof load zone map above.

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. 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. 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. This means that one is a fixed node and the other is a rolling node.

Roof loads are a downward vertical force on the home. 3 20 residential structural design guide.