3 20 residential structural design guide.
Roof design loads.
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.
15 psf x 14ft 210 pounds per lineal foot.
Roof load live load design is affected by the shape of the roof whether it is flat curved or pitched.
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.
The amount of weight a truss needs to support per square foot is important.
50 psf x 14ft 700 pounds per lineal foot.
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.
This includes all of the roofing material and ceiling along with loading for construction purposes and then environmental factors such as wind and snow.
Framing table for maximum roof rafter spans.
Loads used in design load equations are given letters by type.
This means that one is a fixed node and the other is a rolling node.
For a larger map with greater detail refer to asce 7 98.
A fixed node will provide support in both directions down the length of the roof truss members often called the x and y directions.
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.
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.
The north zone middle zone and the south zone are identified on the roof load zone map above.
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.
Chapter 3 design loads for residential buildings.
This downward imposed load on the home is also known as the snow load.
D dead load l live load l.
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.
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.
