There are many ways to get the information and numbers you need to cut a roof. Carpenters and homebuilders depend on a variety of resources to get that information. Among those items available to a roof cutter are rafter tables, trig calculators, construction calculators, how to books and computer programs.
I've used most of those options, and although they did the job, they do have their drawbacks. Calculators can malfunction or be dropped or crushed on the jobsite. Rafter tables are just that, with no back up information for that tough to cut roof. Computers must be used offsite for a print out to be used. If numbers where entered in wrong or conditions on site changed you still need an alternative resource. You could use a laptop, but few users want to subject them to the rigors of a construction site, and as with calculators, ther is the malfunction issue.
My choice for roof cutting information and rafter lengths is A. F. J. Riechers "The Full Length Roof Framer". Its a hardcover book small enough to put in your hip pocket or in a pouch in your nail apron. The information you need is always at your finger tips.
"The Full Length Roof Framer" has rafter tables in half inch increments, giving roof pitches from 1/2 in 12 to 24 in 12. It gives rafter lengths for spans up to fifty feet for common, hip, and valley rafters. There are 144 rafter tables and 2,400 common rafter lengths and 2,400 hip rafter lengths per pitch to 1/8 of an inch.
This book not only gives you all the rafter lengths you'll ever need, but it also guides you step by step through the roof cutting process, whether it be a gable roof or a hip roof. If you have never cut a roof before or only dabbled in roof cutting,
anyone with a working knowledge of a circular saw and a framing square can cut a roof with this book.
Some of the topics covered in "The Full Length Roof Framer" are, Laying out, Cuts for commom, hip, valley, and jack rafters, backing cuts, overhangs, ridges and even cuts on roof sheathing and shingles. Each table has an explanation on how to use it so you don't have to keep thumbing through the book for information. Also on that page is the difference in length for jack rafters for any centers (16,24,36,etc.) that might be used.
This book was copywritten by A. F. J. Riechers in 1917 and all the information in it is as relavent today as it was then. By keeping this book on the jobsite with you, you'll never be without the information you need to cut a roof.
Mike Merisko (C) 2006www.sawkerfs.com