Roof pitch vs. Ridge beam

[3design]

What is the lowest slope of a roof that can/should be built, before you need to move from ridge board/collar ties to ridge beam only? I have a 4:12 that I am trying to build with collar ties and ridge board, will this work?

TIA
Rob G.

[Rich]

Whats the span of the roof - outside of wall to outside of wall? Anything more than 12' and I think you would probably be better off going to a glu-lam ridge beam with increased column size under each end. Anything over 12' and the collar ties get a little too long to be effective.

[3design]

The span is 29'-4". Now I could probably construct a ridge beam and rafters or get some engineered trusses. Thanks for the info. Is there anything in the IRC that could of pointed me in the right direction on this matter? or a book/website?

Thanks

[Rich]

You know I've seen some rafter span tables and only an inkling as to the collar ties. Essentially the article on collar ties from www.taunton.com stated that anything 3:12 and less would need only a ridge beam. Most of the information I found was by a search on google for "rafter span collar tie" without the quotes.
If it were me, at that distance, I would probably go with engineered trusses.