Rain Loading Configuration On A Roof

The key to managing rain loads in buildings is roof drainage including a primary drainage system and a secondary drainage system which is set at an elevation higher than the primary system to drain any water that builds up after the lower system is blocked or not working.

Rain loading configuration on a roof.

The event that shall be considered is an intense short duration rainfall. Special loads such as flood loads ice loads and rain loads are not addressed herein. The reader is referred to the asce 7 standard and applicable building code provisions regarding special loads. 1611 1 design rain loads each portion of a roof shall be designed to sustain the load of rainwater that will accumulate on it if the primary drainage system for that portion is blocked plus the uniform load caused by water that rises above the inlet of the secondary drainage system at its design flow.

3 2 load combinations the load combinations in table 3 1 are recommended for use with design. Each portion of a roof shall be designed to sustain the load of rainwater that will accumulate on it if the primary drainage system for that portion is blocked plus the uniform load caused by water that rises above the inlet of the secondary drainage system at its design flow. D h additional depth of water above the secondary inlet undeflected roof at its design flow hydraulic head it appears as though this is applied as a uniform load when viewing the examples in the commentary. D s depth of water on undeflected roof up to the inlet of the secondary drainage system.

Should your roof installation have to be delayed due to poor weather be patient. The accumulation of water caused by the deflection of the roof structure is called ponding and as it results in added load it can lead to roof instability. This is all of the natural stresses imposed upon a roof such as snow loads rain loads and wind loads. Note that although rain loads are covered in ibc section 1611 they were not required to be listed on the construction documents.

It is not the fault of your contractor and while the delays can certainly be frustrating a contractor who attempts to install a new roof in the rain is going to be compromising the overall integrity of the installation. Wind loads depend on wind speed and can vary as widely as the snow. This is highly regional as weights of snow for example range from 10 to 300 pounds per square foot based on moisture and volume of the snow. Nominal loads is essentially unaffected.

Until recently floor live load roof live load roof snow load wind load earthquake design data and flood loads were required to be listed on the construction documents. Note that although rain loads are covered in ibc section 1611 they were not required to be listed on the construction documents.