Framing for Roof Dormers

Now, since the run of the small gable is 8 feet, measure back 8 inches on square No. 1 and draw the lines C-D and D-F' at right angles from the tongue of the respective squares. A-F' will represent the short valley, and A-F the corresponding common rafter to a scale of one inch to the foot. The figures shown on the square intersected by the lines A-E and A-E' will give the seat and plumb cuts of the com mon and valley rafters respectively. The length of the diagonal lines on the squares are and 15 inches, and these figures taken on the blade of the respective squares will give the side cuts for the valley and jack rafters.

In this illustration we have used two scales— the full scale on the steel square for a one foot run, to obtain the cuts; and the scale, or one inch to the foot run, for the diagram of the roof, from which to obtain the length of the rafters. The fact that there are two scales employed may render the subject harder to grasp by some; but we trust that after a little study of this illustration will be clear.

The reader will observe that in all of our work we have adhered to 12 on the tongue as the starting point. We do this because it repre sents unity or the beginning, and therefore answers for auy run or pitch given the roof. However, as a comparison, it might be well to illustrate this problem by the one-inch scale to the foot.

Bear in mind that while we illustrate these problems with two squares, only one is neces sary, as the angles may be laid' out with the different positions of the square and the required proportions taken on the same. As

the run of the small gable is 8 feet, place the blade of square No. 2 at 8 on both the tongue and blade (Fig. 62), with the heel opposite 14 of square No. 1 (because 14 represents the rim of the main roof). Now, since the rise is 9 inches to the foot, for 14 feet it would be 10 feet 6 inches. Then the line from to 101/2 Fig. 62. Steel Square in Roof Dormer Training.

will be the same length as A E' of like letters in the previous illustrations. By drawing the line D-F' at right angles to the blade, A-F' will represent the length of the short valley.

Dimensions, 40 by 54 ft., with 20-ft. posts, all mortised and pinned. Posts are S by S in and there is no pieee lighter than 4 by 6. On each corner is a brace mortised in the sill and plate, 6 by S in., and girders mortised in same. This gives a bracing of great strength against wind pressure. Lower rafters have two-third pitch; upper ones, one-third pitch.

As for the length of the common rafters, this is an easy matter to get by the scale method, by simply taking the run and rise of the roof on the tongue and blade and measuring diagon ally across. However, while this does for work ing purposes for the more common run of work, it is not absolutely a correct method, because the least variation is magnified twelve-fold.