oards
shall not be less than 7/8ths of an inch thick.

There is little difference in the requirements of the various
localities. For example, the regulations of the Croydon council
require that every common bearing joist for lengths up to 3 ft. 4 in.
in clear shall be 3 in. X 2-1/2 in.; for lengths between 3 ft. 4 in.
and 5 ft. 4 in., 4 in. X 2 in.; for lengths between 5 ft. 4 in. and 7
ft. 4 in., 4 in. X 3 in.; and so on according to the clear span. The
Croydon by-laws with regard to trimmers are as follows:--A trimmer
joist shall not receive more than six common joists, and the thickness
of a trimming joist shall be 1-1/2 in. thicker than that for common
joists of the same bearing, and the thickness of a trimmer joist shall
be 1/4 in. thicker for every joist trimmed into same than the common
joist. For example, if the common joists are 4 in. X 3 in. the
trimming joists would have to be 4 in. X 4-1/4 in., and the trimmer
joist would have to be 4 in. X 4-1/2 in.

_Partitions._--Partitions are screens used to divide large floor
spaces into smaller rooms and are sometimes constructed to carry the
floors above by a system of trussing. They are built of various
materials; those in use now are common stud partitions, bricknogged
partitions, and solid deal and hardwood partitions, 4-1/2 in. brick
walls or bricks laid on their sides, so making a 3 in. partition, and
various patent partitions such as coke breeze concrete or hollow brick
partitions (see BRICKWORK), iron and wire partitions, and plaster slab
partitions (see PLASTERWORK).

There are two kinds of stud or quarter partitions, common and trussed.

[Illustration: FIG. 30.--Common Partition.]

Common partitions.

Common partitions (fig. 30) simply act as a screen to divide one room
from another, and do not carry any weight. They weigh about 25 lb. per
foot superficial including plastering on both sides, and are composed of
4 in. X 3 in. head and sill and 4 in. X 2 in. upright studs; 4 in. X 2
in. nogging pieces are fitted between the studs to keep them from
bending in, and are placed parallel with the head, usually 4 ft. apart.
Where door-openings occur in these partitions the studs next the opening
are 4 in. X 3 in. Should the floor boards have been laid, the sill of
the partition would be laid direct on them, but if the partitions are
erected at the time of building the structure the sill should either
rest di