Roof Rafter Deflection Limit

See the table below.

Roof rafter deflection limit.

L 720 l 600 l 480 l 360 l 240 l 180. The maximum allowable deflection of a ceiling is expressed as a fraction in the format l x. On a roof with a slope greater than 4 to 12 the live load limit is typically adjusted downward from 20 psf to 15 psf to allow for the relatively greater dead load on the steeper roof. For example the allowable deflection of a 12ft span floor joist with plaster l 360 is 0 4 12ft divided by 360.

The l is the length in inches of the clear span of the joists or rafters that make up the ceiling. Clear span in inches l over a given number. Supporting roof and floor. Spacing in 12 16 19 2 24.

So these are the limits set by the code. If that same joist had gypsum ceiling l 240 the allowable deflection is 0 6. Ridge beam single span. You can also use af pa s span tables for joists and rafters.

Maximum deflection limits are set by building codes. 2 are indicated below. 2x4 2x6 2x8 2x10 2x12. Roof beam single span.

Douglas fir maximum horizontal roof rafter span for lumber grade selected structural and no. Roof beam double span. Live load is weight of furniture wind snow and more. The code section on working load deflection states.

For continuous aluminum structural members supporting edge of glass the total load deflection shall not exceed l 175 for each glass lite or l 60 for the entire length of the member whichever is more stringent. Ridge beam double span. And l 180 for unplastered roof construction. L 240 for unplastered floor construction.

Dead load weight of structure and fixed loads 15 lbs ft2. For sandwich panels used in roofs or walls of sunroom additions or patio covers the total load deflection shall not exceed l 120. The deflection of floor and roof assemblies shall not be greater than l 360 for plastered construction. 1 psf lbf ft2 47 88 n m2.

A floor joist appropriately selected to span 10 feet with an l 360 limit will deflect no more than 120 360 1 3 inches under maximum design loads. This is the easiest way to determine allowable dead loads live loads and deflection limits. Note it gives the allowable deflection based on a fractional span quantity so a larger denominator will yield less deflection. This publication has a much more extensive.

3 stud construction standard utility.