Help with Live Load Span

[Francis Vineyard]

In accordance with Section R301.7 why doesn't the floor joist span tables use L/240 as permitted in the referenced tables and (2015) R502.5(3)?

R301.7 Deflection. The allowable deflection of any structural member under the live load listed in Sections R301.5 and R301.6 or wind loads determined by Section R301.2.1 shall not exceed the values in Table R301.7.

 

[Paul Sweet]

Why does Note b say L/240 and the note below the title say 360?

 

[Francis Vineyard]

That's part of my question; why 360 for the floor spans in Table R502.3.1(2) but L/240 for open porch (exterior) floor spans?

 

[tmurray]

My guess would be that the same level of stiffness required of regular floors are not necessarily expected of porch floors.

 

[Francis Vineyard]

Doesn't Section R301.7 permit the lower deflection with longer joist span for regular floors?

 

[Phil]

I am not familiar with the IRC. For floor members in the IBC, the live load deflection limit is L/360 and the live+dead load deflection limit is L/240. Maybe some of the deflection in the IRC is similar.

 

[Francis Vineyard]

Phil, could we assume the header span has a deflection of L/240 for exterior walls for floors with a dead load of 20 psf. and not 10 psf?

Is this logical for decks and open porches too?