The proper construction of a roof depends in a great measure upon the shape of the roof, the size and arrangement of the building and the use that is to be made of the enclosed space or "attic."

The shape of the roof will be governed principally by the size and plan of the building, the external effect sought and whether or not the roof space is to be finished.

Before describing the methods of construction, it seems desirable to consider briefly the various shapes of roofs and to define the principal parts.

All roofs which have an inclination of 200 or more with a hori-zontal plane are called "pitch" roofs, and those whose inclination is less than this are called "flat" roofs.

The "pitch" of a roof is the angle of inclination which the rafters make with a horizontal plane; it is sometimes expressed in degrees, but more often by the proportion which the height in the centre bears to the span, or by the rise in inches for each foot of half span. The last method is the simplest and least likely to be misunderstood, and is preferred by the author.

Below is given the rise and angle for the most common pitches:

Two-thirds pitch......

rise,

16

ins.

in

1

ft.;

angle,

53°

52'

Half pitch (square pitch)...........

"

12

ins.

in

1

ft.;

"

45°

One-third pitch..........

"

8

ins.

in

1

ft.;

"

33°

41'

One-fourth pitch...........

"

6

ins.

in

1

ft;

"

26'

34'

.......................................

"

7

ins.

in

1

ft.;

"

30°

15'

In deciding on the pitch of the roof for any given building the following conditions should be considered : Appearance (in connection with the style of architecture), climate, nature of the covering and cost In dwellings, churches, etc., external appearances generally determines the pitch, while for factories, sheds, etc., the last two conditions are usually the controlling ones.

High pitched roofs are considered best adapted to climates which have considerable rain and snow, as in our Northern States, while a low pitch with heavy projections seems most suited to warm climates.

The most economical pitch for small buildings is that which has a rise of about 9 or 10 inches to the foot ; and for trussed roofs, about 300. Shingle roofs should have a pitch of at least 6 inches to the foot, except on sheds and porches, where it may, if necessary, be reduced to 4 inches. Roofs covered with slates of large size may be made as flat as 5 inches to the foot, but a steeper pitch is to be preferred. Clay or metal tiles should in general have a pitch of at least 7 inches to the foot, and for a desirable effect a square pitch is necessary. The relation of the pitch to the roof covering will be more fully considered in Part III.