roof as for any other part of the building. By the use
plates, are the principal members of roof framing it is
of this common unit of measurement the framing
important to understand the following terms that
square is employed in laying out large roofs (1, 2, fig.
apply to them:
(1) Common rafters. The common
(5) Rise in inches. The rise in inches
rafters, AAA, extend from plate to ridge-board at
is the number of inches that a roof rises for every foot
right angles to both (1, fig. 2-12).
(2) Hip rafters. Hip rafters, DD,
(6) Pitch. Pitch is the term used to
extend diagonally from the corners formed by
describe the ratio of rise to roof span (2, fig. 2-11).
intersection plates to the ridgeboard (1, fig. 2-12).
(7) Cut of roof. The cut of a roof is
(3) Valley rafters. Valley rafters, CC,
the rise in inches and the unit of run (12 inches). See
extend from the plates to the ridgeboard along the
2, fig. 2-11.
lines where roof slopes intersect (1, fig. 2-12).
(8) Line length. The term line length
(4) Jack rafters. Jack rafters never
extend the full distance from plate to ridge-board.
triangle whose base is the total run and whose
Jack rafters, BBB, are shorter than common rafters
altitude is the total rise (1, fig. 2-11).
and their lower ends rest on the plate and their upper
ends against the hip rafter (1, fig. 2-12).
(9) Plumb and level lines. These
terms have reference to the direction of a line on a
(5) Cripple jacks. Cripple jacks, FF,
rafter and not to any particular rafter cut. Any line
are nailed between hip and valley rafters (1, fig. 2-
that is vertical when the rafter is in its proper position
is called a plumb line. Any line that is level when the
(6) Top of plumb cut is the cut made
rafter is in its proper position is called a level line (3,
at the end of the rafter to be placed against the
ridgeboard or, if the ridgeboard is omitted, against
the opposite rafters (2, fig. 2-12).
a. General. The members which make up
(7) Seat, bottom, or heel cut is to rest
the main body of the frame work of all roofs are
on the plate (2, fig. 2-12).
called rafters. They do for the roof what the joists do
(8) Side or cheek cut is a bevel cut on
for the floor and what the studs do for the wall.
the side of a rafter to fit it against another frame
Rafters are inclined members which vary in size,
member (2, fig. 2-12).
depending on their length and the distance at which
they are spaced. The tops of inclined rafters are
(9) Eave or tail is the overhang of the
fastened in one of the various common ways
rafter extending beyond the outer edge of the place
determined by the type of roof. The bottoms of the
(2, fig. 2-12).
rafters rest on the plate member which provides a
(10) Rafter line length is measured
connecting link between wall and roof and is really a
along the upper edge of the rafter and is the distance
functional part of both. The structural relationship
from the ridge line to a point marking the intersection
between rafters and wall is the same in all types of
of the upper edge of the rafter with the building limit
roofs. Rafters are not framed into the pate but are
simply nailed to it, some being cut to fit the plate
while others, in hasty construction, are merely laid on
RAFTER DESIGN AND LAYOUT
top of the plate and nailed in place. Rafters may
Rafters must be laid out and cut with slope,
extend a short distance beyond the wall to form the
length, and overhang exactly right so that they will fit
eaves and protect the sides of the building.
when placed in position. If detailed building plans
b. Types of rafters and rafter cuts (fig.
are available this
2-12). Since rafters, together with ridge-boards and