**(1) Span. **The span (1, fig. 2-11) of

any roof is the shortest distance between the two

opposite rafter seats. Stated in another way, it is the

measurement between the outside edges of the

outside-wall plates, measured at right angles to the

direction of the ridge of the building.

**(2) Total rise. **The total rise (1, fig. 2-

11, fig. 2-13) is the vertical distance measured from

the intersection of the upper edge of the rafter with

the building limit line, to the top of the ridge. It is the

product of the rise in inches times the total run in

feet.

**(3) Total run. **The term total run (1,

fig. 2-11) always refers to the level distance over

which any rafter (para 5a) passes. For the ordinary

gable-roof rafter, this would be one half the span

distance.

The unit of

**(4) Unit of run.**

measurement, 1 foot or 12 inches, is the same for the

*Figure 2-10. Types of roofs.*

in a different direction. This type of roof is seldom

used in TO construction, since it is complicated and

requires much time and labor to construct.

**e. Slope or cut**. The slope of a roof is the

angle which the roof surface makes with a horizontal

plane. The surface may vary from absolutely flat to a

steep slope. The usual way to express roof slope is

by means of numbers; for example, 8 and 12, 8 being

the rise and 12 the unit of run. Occasionally roof

slope is given on plans with some other run than 12,

the unit of run. For example, suppose a plan gives

the rise as 2 inches per 5 inches of run. In this case

the slope can be converted to the standard unit of run