As per standards, the Roof beams should have a continuous upward slope equivalent to 1/4 in/ft ( 20.8 mm/m) between a drain and the high point of a roof, in addition to minimum recommended camber to avoid ponding.
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Timber coloums are seldom used singly. Mostly they are a group of lumber which are stick together to form a single member. The allowable unit stress on timber is calculated by using the following formula
When the Columns have square or rectangular cross section
When the Columns have circular cross section