Roof Live Load Deflection Limit

So if you have a beam 20ft long the allowable deflection limit is 20ftx12in ft 240 1 inch if using l 240.

Roof live load deflection limit.

And l 180 for unplastered roof construction. Used but they typically defined the load cases or combination stress or strength limits and deflection limits. Figure 2 live loads and deflection limits are set by code. D dead load l live load l r live roof load w wind load s snow load e earthquake load r rainwater load or ice water load.

These limit states are mathematic expressed as. The code section on working load deflection states. L 240 for unplastered floor construction. These tables are from the icc international residential code.

For structural roofing and siding made of formed metal sheets the total load deflection shall not exceed l 60. Load types loads used in design load equations are given letters by type. 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. This sets an allowable first floor live load of 40 psf a dead load of 10 psf and a deflection of l 360.

The table of contents indicates that table f 2 matches these loading conditions. D ll l 360. Select the appropriate table in span tables for joists and rafters. This means that your actual calculated deflection of the beam should not exceed either 1 inch or 0 67 inch depending on which of the criteria you are using.

Table r301 7 allowable deflection of structural members. D tl l 240. The l stands for length. Step 2 span table.

For example the allowable deflection of a 12ft span floor joist with plaster l 360 is 0 4 12ft divided by 360. For secondary roof structural members supporting formed metal roofing the live load deflection shall not exceed l 150. For secondary wall members supporting formed metal siding the design wind load deflection shall not exceed l 90. You can also use af pa s span tables for joists and rafters.

Or 20ftx12in ft 360 0 67 inch if using l 360. So these are the limits set by the code. In the absence of more specific criteria criteria for structures with brittle finishes as found in code documents for years is frequently used. The deflection of floor and roof assemblies shall not be greater than l 360 for plastered construction.

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.