ontally in the wall, a horizontal course, usually of
asphalt, in the thickness of the floor, and also a vertical damp-proof
course from a level below that of the floor to about 6 in. above the level
of the ground, either built in the thickness of the wall or rendered on the
outside between the wall and the surrounding earth (fig. 10).

By means of dry areas or air drains (figs. 11 and 12), a hollow [v.04
p.0526] space 9 in. or more in width is formed around those portions of the
walls situated below the ground, the object being to prevent them from
coming into contact with the brickwork of the main walls and so imparting
its moisture to the building. Arrangements should be made for keeping the
area clear of vermin and for ventilating and draining it. Dry areas, being
far from sanitary, are seldom adopted now, and are being superseded by
asphalt or cement applied to the face of the wall.

[Illustration: FIG. 10.]

[Illustration: FIG. 11.]

[Illustration: FIG. 12.]

Moisture is prevented from soaking down from the top of the wall by using a
covering of some impervious material in the form of a coping. This may
consist of ordinary bricks set on edge in cement with a double course of
tiles immediately below, called a "creasing," or of specially made
non-porous coping bricks, or of stone, cast-iron, or cement sloped or
"weathered" in order to throw the rain off.

[Illustration: FIG. 13.]

The exterior of walls above the ground line may be protected by coating the
surface with cement or rough cast; or covering with slates or tiles fixed
on battens in a similar manner to those on a roof (fig.13).

The use of hollow walls in exposed positions has already been referred to.

The by-laws dated 1891, made by the London County Council under section 16
of the Metropolis Management and Buildings Acts Amendment Act 1878, require
that "every wall of a house or building shall have a damp course composed
of materials impervious to moisture approved by the district surveyor,
extending throughout its whole thickness at the level of not less than 6
in. below the level of the lowest floor. Every external wall or enclosing
wall of habitable rooms or their appurtenances or cellars which abuts
against the earth shall be protected by materials impervious to moisture to
the satisfaction of the district surveyor..." "The top of every party-wall
and parapet-wall shall be finished with one course of hard, well-burnt
bricks set on edge, in ce