Cantilivered spans with roof loads

[Yankee]

Table R502.3.3(1),

Could someone explain to me what is meant by the "roof width" values? Is this the . . . width of the roof at the wall being supported on the catiliver? Which direction is "width"?

thanks : /

 

[Francis Vineyard]

The width is same as twice the rafter span. The cantilevered floor will have additional weight to support the wider the roof; hence increase suface area.

 

[Yankee]

The width is same as twice the rafter span. The cantilevered floor will have additional weight to support the wider the roof; hence increase suface area.

So, if I understand what you described, we are talking about a gable roof with the eve ends bearing along a wall(s) sitting on a cantilevered floor system? And the gable roof is, or is not, supported by a structural ridge? And what about if it was a shed roof with the lower edge sitting on the cantilevered wall? I am seeing so many scenarios where this number isn't working for me (?)

 

[Francis Vineyard]

Yes, agreed; the number may seem conservative.

What about joist running parallel to the rafters and the floor is cantilevered out the gable end; what is the calculated load for the particular roof projection slope? Do we measure the clear span across the ridge beam of a cathedral roof? What about the load bearing from hips; intersecting and flat roofs?

Foot note “a. Tabulated values are for clear-span roof supported solely by exterior bearing walls.”

Define clear-span to mean from load point to load point such as from a purlin to the exterior wall?

I see the IRC dealing with conventional framing prescribed with conservative margin of tolerances; a safety factor that cannot anticipate every possible case.

Aside from the above issues; notice the table is limited to 48”; may have to be professionally designed to offset for brace walls if one wanted to calculate or interpolate 2x12’s in the first column.