Very little, if anything, new will be found in the following pages. The object in writing them has been to bring together in a small compass all the essentials required in properly designing ordinary roof-trusses in wood and steel.<br><br>At present this matter is widely scattered in the various comprehensive treatises on designing and in manufacturers' pocket-books. The student who desires to master the elements of designing simple structures is thus compelled to procure and refer to several more or less expensive books.<br><br>Students in mechanical and electrical engineering, as a rule, learn but little of the methods of designing employed by students in civil engineering. For this reason the writer has been called upon for several years to give a short course in roof-truss design to all students in the Junior class of the Rose Polytechnic Institute, and in order to do so he has been compelled to collect the data he has given in this book.<br><br>The tables giving the properties of standard shapes are based upon sections rolled by the Cambria Steel Company. Standard sections rolled by other manufacturers have practically the same dimensions.