Shed Dormer

[westchester777]

i was asked to size a ridge beam for a 28'w x 40' long
attic that is presently 10:12 pitch and will have a 3:12 shed dormer one side 34' long

not wanting to take chances i designed it to be
full structural ridge. but thats probably overkill.
our live loads are 45psf.

i am an architect so not versed in how to calculate sloped rafter reactions. i use enercalc and beamchek software
for beams and columns

is there a simple way to look at this? or software
that does sloped roofs?

thanks

 

[sturr]

I think you have done it right. Unfortunately, unless you can provide "truss action" through the rafters and a tension member (which would be possible if the rafters intersected the floor line) the sloping members are treated as typical joists hanging on a beam. Keep in mind the "span" of the rafters need only be the horizontal distance.

 

[tdsull]

With a shed dormer on one side of your roof you do not acheive a typical tie roof system. A structural ridge beam is not overkill by any means. Roof live loads are based on the horizontal projection. If your house width is 28' your tributary area is 14'.