show that a rafter with a run of 12 and a rise of 4 has

A collar beam or tie is a piece of stock (usually 1

one-sixth pitch, 12 and 6 has one-fourth pitch, and 12

by 4, 1 by 6, or 1 by 8) fastened to a pair of raters in a

and 12 has one-half pitch. To use this scale for a roof

horizontal position part way between the top plate

with one-sixth pitch (or a rise of one-sixth of the

and the roof ridge as shown in figure 2-18. These

width of the budding) and a run of 12 feet, find 1/6 in

beams keep the side walls of the building from

the table, follow the same line of figures to the right

spreading. The lower the collar beam or chord, the

until directly beneath the figure 12, which is the run

better it fulfills its purpose. This type of bracing is

of the rafter. Under the figure 12 appear the numbers

used in the roofs of small buildings where no ceiling

12, 7, 10, which is the rafter length required and

joists are used.

which represents 12 feet, 7 inch and 10/12 of an inch.

They are written as follows: 12 feet 7 10/12 inches.

For a pitch of one-half (or a rise of one-half the width

of the building) and a run of 12 feet, the rafter length

is 16, 11, 6 or 16 feet, 11 6/12 inches.

table in figure 2-17 is used as follows: Using a run of

27 feet, find the length for a run of 23 feet, then find

the length of 4 feet and add the two. The run for 23

feet with a pitch of one-fourth is 25 feet, 8 5/12

inches. For 4 feet, the run is 4 feet, 5 8/12 inches.

The total run for 27 feet is 30 feet, 2 1/12 inches.

When part of the run is in inches, the rafter table

reads inches and twelfths instead of feet and inches.

For example, if the pitch is one-half and the run is 12

feet, 4 inches, add the rafter length of a 12-foot run to

that of a rafter length of a 4-inch run, as follows: For

a run of 12 feet and one-half pitch, the length is 16

feet, 11 6/12 inches. For a run of 4 inches and one-

half pitch, the length is 5, 7, 11. In this case the 5 is

inches, the 7 is twelfths, and the 11 is 11/12 of 1/12,

which is nearly 1/12. Add it to the 7 to make it 8,

singly; they are usually assembled into trusses, as

making a total of 5 8/12 inches, then add the two

shown in figure 2-19. Two rafters are connected at

lengths together. This sum is 17 feet, 5 2/12 inches.

the top by using a rafter or collar tie well nailed into

The lengths that are given in the table are the line

lengths; the overhang must be added. After the

accuracy of the rafter cuts should be checked by

length of the rafter has been found, the rafter is laid

spreading the lower ends of the rafters to correspond

out as explained in **a **above.

to the width of the building.

This may be

accomplished by a template, or by measuring the

distance between the seat cuts with a tape.

rafter is usually cut square to save time. When the

roof has no overhang, the rafter cut is plumb, but no

notch is cut in the rafter for a seat. The level cut is

20-foot-wide, TO type building are made from the

made long enough to extend across the plate and the

following members (fig. 2-19).

wall sheathing. This type of rafter saves material,

although little protection is given to the side wall.