Roof Deflection Limits

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.

Roof deflection limits.

Living room floors l 360 40 psf. Bedrooms and habitable attic floors l 360 30 psf. D ll l 360. So these are the limits set by the code.

Examples of code prescribed deflection limits and live load values are. Chapter 3 of the international residential code irc provides the maximum allowable deflection for a given structural member floor roof wall etc. These limit states are mathematic expressed as. For the purpose of the determining deflection limits herein.

L 240 for unplastered floor construction. And l 180 for unplastered roof construction. For aluminum structural members or panels used in roofs or walls of sunroom additions or patio covers not supporting edge of glass or sandwich panels the total load deflection shall not exceed l 60. Load limits on the roof of a building.

Roofs are under a lot of pressure. See the table below. The deflection of floor and roof assemblies shall not be greater than l 360 for plastered construction. 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.

The code section on working load deflection states. 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. 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. B for cantilever members l shall be taken as twice the length of the cantilever.

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. For floor trusses the deflection in inches due to live load cannot. Note it gives the allowable deflection based on a fractional span quantity so a larger denominator will yield less deflection. D tl l 240.

Typically codes set deflection limits for roofs walls and floors. Codes provide the maximum allowable deflection limits for floor and roof trusses which is based solely on the truss span.