Rule Of Thumb For Roof Loading

Its earliest 1685 appearance in print comes from a posthumously published collection of sermons by scottish preacher james durham.

Rule of thumb for roof loading. The exact origin of the phrase is uncertain. In areas with mild climates patio roofs are generally designed for loads of 30 psf pounds per square foot. 1 where l is the rafter length projected onto the horizontal plane d is the rafter tributory width and σ is the roof loading projected onto the horizontal plane. And the back span has to be at least twice the cantilever distance.

The tables below give maximum spans for rafters and beams. Here each square foot of roof system delivers 50 pounds of live load and 15 pounds of dead load 65 psf total to the structural support system. 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. For heavy roofs or in areas with substantial snowfall or winds call your local building department for code requirements.

Beam depths are typically 5 1 2 inches 7 1 4 inches 9 1 4 inches 11 1 4 inches 11 7 8 inches 14 inches 16 inches 18 inches and 20 inches. The use of projections onto the horizontal plane seems to be the most commonly used approach. The higher tonnage and airflow values correspond to buildings that are located in hotter more humid climates because the primarily load within these types of buildings will be due to the large. Many profest christians are like to foolish builders who build by.

The total load on a rafter is given by w which is calculated using equation 1. In english rule of thumb refers to an approximate method for doing something based on practical experience rather than theory. The figures are based on quality materials. It is important to note however that the depth of a member is influenced not only by the span but by such variables as spacing loads support conditions deflections and clearance require.

To prevent dangerous building loading or even structural collapse roof drainage systems using an internal or piped roof drain system should provide for overflow drains to handle excess water volume and weight loading should the roof drainage system become blocked or prove inadequate in unusual conditions. Design a beam depth based on the rule of thumb for estimating the depth of manufactured beams which is to divide the span by 20. Remember these loads are distributed uniformly over the entire surface of the roof.