# how to use a framing square

Posted by bryan gouin on June 13th, 2001 09:34 PM
In reply to Framing square by Jeff on December 23rd, 2000 06:29 AM [Go to top of thread]

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 Moderator Post (s) for this thread:> by doug seibert on 04/08/2005 > by doug seibert on 05/22/2005

on the side of a framing square you have your charts for calculating different types of rafters and also it gives you the angles of the side cuts of hip and valley rafters and it also gives you the difference in the length of hip and valley jack rafters 24 or 16 inch on center so you don't have to measure every one of them. i use it for much more than just rafters,angles on skirt boards,the chart for mathamatically squaring in tough places and much much more. how to use for calculating common rafters off the chart----- first decide what your roof pitch is example 6-12 what does this mean? it means for every 12'' you come over if you measure straight up you will have 6'' now to get the length of the third side of this triangle or the hypotonoise all you have to do is look at your chart on the side of the framing square under the heading common rafter, look under 6 because you are using a 6-12 and this is your hypotonoise 13.42 so lets say your house is 28' deep and you want to use a 6-12 pitch what you have do is take half of your 28' which is 14' multiply 14 times 13.42 because we know for every 12'' we come over the hypotonoise is 13.42 so if we go over 14' we have to multiply 13.42 14 times which equals 187.88, this is the length of your rafter , to convert .88 to 16ths of an inch multiply .88 times 16 14.08 round down 14/16 or 7/8 the rafter length is 187 and 7/8 of an inch now if you have all that you have to still figure out half of your ridge board and your overhang and birds mouth but i hope i have given you a basic understanding of how to calculate rafters its hard for me to explain without pictures, though i am a master carpenter i am a far cry from a computer wizard .