ladder is required for temporary purposes only; but as we are of course
aiming at the construction of a thing made to last, we shall go to the
trouble of "notching-in" each rung (see Fig. 10), so that the sides shall
take the weight directly, and the nails only have to keep the rungs firmly
in position. The objection to notching-in is that it reduces the strength
of the ladder, which is of course only that of the wood between the bottom
of the notches and the plain side. Therefore it is necessary to have sides
somewhat deeper than would be required for a centrally-runged ladder;
which is pierced where the wood is subjected to little tension or
compression.

[Illustration: Fig. 10--House ladder and details of letting in a rung]

Materials.--The length of the ladder will decide what the stoutness of
the sides should be. For a ladder about 12 feet long, such as we propose to
describe, larch battens 3 by 1-1/8 inches (actual) in section and free from
knots, especially at the edges, will be sufficiently strong to carry all
reasonable weights without danger of collapse. But be sure to get the best
wood obtainable. The rungs may be of 2 by 1 inch stuff, though 2 by 3/4
inch will suffice for the upper half-dozen, which have less wear, and are
shorter than those below.

The rungs are 10 inches apart (Fig. 10), centre to centre. The distance may
be increased to a foot, Or even more if weight-saving is an object.


CONSTRUCTION.

Preparing the Sides.--These are cut to exactly the same length, which we
will assume to be 11 feet 6 inches, planed quite smooth and rounded off