Roof Deflection Limits

In any given room the framing in the ceiling is really just the framing for the floor of the room above it or for the roof.

Roof deflection limits.

The international codes i codes are the widely accepted comprehensive set of model codes used in the us and abroad to help ensure the engineering of safe sustainable affordable and resilient structures. These limit states are mathematic expressed as. L 240 for unplastered floor construction. Typical deflection limits referenced in code books are l 360 l 240 or l 180.

Note it gives the allowable deflection based on a fractional span quantity so a larger denominator will yield less deflection. Load limits on the roof of a building. In order to stay intact and in place a roof must be able to resist loads both permanent and temporary that are pushing. D tl l 240.

Bedrooms and habitable attic floors l 360 30 psf. Living room floors l 360 40 psf. The deflection of floor and roof assemblies shall not be greater than l 360 for plastered construction. Examples of code prescribed deflection limits and live load values are.

Codes provide the maximum allowable deflection limits for floor and roof trusses which is based solely on the truss span. See the table below. B for cantilever members l shall be taken as twice the length of the cantilever. These limits are based on live loads and activities experienced in specific rooms of a house.

So these are the limits set by the code. Generally for roof trusses the deflection in inches due to live load cannot exceed the span in inches divided by 240 l 240 and due to total load l 180. For the purpose of the determining deflection limits herein. This simplistic criteria puts a limit of the span divided by 360 on the incremental deflection due to live or transient load only and a limit of the span divided by 240 on deflection under total load.

The international code council icc is a non profit organization dedicated to developing model codes and standards used in the design build and compliance process. Roofs are under a lot of pressure. D ll l 360. Typically codes set deflection limits for roofs walls and floors.

And l 180 for unplastered roof construction. The code section on working load deflection states.