line of bridging should be placed, and on joists more
an opening is to be left in the floor for some other
than 16 feet long, two lines.
structure. The timbers on each side of such an
opening are called "trimmers," and these must be
1-34. SUBFLOOR
made heavier than the ordinary joists. A piece called
a "header" must be framed in between them to
Subfloor, if used, is laid diagonally on the joists
receive the ends of the short joists as shown in figure
and nailed with 8- or 10-penny nails, the number of
1-35. To frame an opening of thin type, first install
nails depending upon the width of the boards.
joists A and C (fig. 1-35), then cut four pieces of
Boards 8 inches wide or over should have three or
timber that are the same size as the joists with the
more nails per joist. Where the subfloor is more than
length corresponding to the distance between the
1 inch thick, larger nails should be used. By the use
joists A and C at the outside wall. Nail two of these
of subflooring, floors are made much stronger since
pieces between the joists at the desired distance from
weight is distributed over a wider area. Figure 1-7
the ends of the joists; these pieces are shown as
shows the method of laying a subfloor. It may be
headers Nos. 1 and 2. Install short joists X and Y, as
laid before or after the walls are framed, preferably
shown. The nails should be 16- or 20-penny nails.
before as it can then be used as a floor to work on
By omitting headers Nos. 3 and 4 and joists B and D
while framing the walls.
temporarily, the short joists X and Y can be nailed in
1-35. REINFORCED JOISTS
place through the header and the headers can be
nailed through the joists A and C into its end. After
In certain parts of the floor frame, in order to
the header and short joists have been securely nailed,
support a bearing partition or some other heavy,
headers Nos. 3 and 4 are nailed beside Nos. 1 and 2.
concentrated load, it may be necessary to construct
Then joist B is placed beside joist A and joist D
reinforced joists (fig. 1-34 (1)). If spacing is required
beside joist C, and all are nailed securely.
for heat ducts, solid blocking should be used between
the joists (fig. 1-34 (2)(A)).
1-37. FOUNDATION LAYOUT
1-36. HEADERS AND TRIMMERS
The objectives of surveying for building
construction are to lay out the proposed
A girder may also be necessary in a floor when
Figure 1-34. Reinforced joists.
1-36
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