is fastened to the lower ends of the rafters. The lower
relocate. When they are no longer needed in one area,
end of the rafter is seated on the top plate of the
they can be shipped to an area where they can serve a
sidewalls, as shown in figure 30. The joint made by the
useful function. We will concentrate our attention upon
joist and rafter is very important The joist helps to
two metal buildings that are frequently used:
prevent the lower end of the rafter and the top of the
advanced base hut and the light steel frame buildings.
wall from moving outward. Perhaps you have noticed
5-2. Advanced Base Hut. The advanced base hut is
buildings where the sidewalls bowed outward and the
usually referred to as a "quonset hut". The standard size
ridge sagged in the middle. This is possible when the
is 20 by 48 feet. However, you will find that some of
rafter and top plate pull loose from the ceiling joist. The
them are two or three times as long as this. They are
load on the rafter forces the upper part of the wall
planned so that they can be assembled in sections 8-foot
outward, and the ridge line becomes lower. This also
lengths to make a building 8, 16, 28, etc., feet long. They
happens in permanent structures but is most common in
are easily adapted for quarters, office space, workshops,
light frames, where fewer and lighter ceiling joist are
training areas, supply storage, or any other function that
can be placed within them. Nails, screws, and bolts used
4-23. The rafter spacing is the same as stud spacing,
in the assembly of the quonset hut are easily removed
4-foot on-center. A knee brace fastened to the rafter,
when repair or disassembly of the unit is required. The
ceiling joist, and wall stud is used every 12 or 16 feet for
primary parts of this hut are the floor and wall, so let's
the length of the building. One-inch sheathing boards
see how they are put together.
are used for the roof deck. Roll roofing is used as the
5-3. Floors. The floor of the hut consists of a metal
roof covering. There is no roof overhang at the eave or
frame with a plywood covering. The main support of the
gable, and the roof covering is lapped down the side walls
building is provided by five girders that run the length of
to prevent leaks along the edge of the roof.
These I-shaped girders are spaced
4-24. The interior of the light frame prefab is usually
approximately 5 feet 1 inch on-center to provide support
open, and leaks are easily located by a visual inspection.
for the floor joists. The girder, as we called it in the
When a ceiling and partitions are used in the building,
wooden building, is referred to as an I-beam (its shape)
you must locate leaks by entering the attic or going on
or joist sill (its function) in metal construction. Joists
the roof. Don't walk around on the roof any more than
spaced 2 feet on-center are placed on, and perpendicular
is absolutely necessary. Instead, you should locate the
to, the joist sills, as shown in figure 31. A U-shaped
leak by entering the attic and checking for water marks.
channel plate fastened to
Then go on the roof and make the repair. Use a 1 x 12
for a walkway and avoid walking between the rafters.
The wide spacing of the rafters allows the decking to sag
when you walk on it Of course, old, brittle roofing may
be broken beyond repair, and the only feasible way to fix
leaks may be to put on new rolled roofing.
4-25. Most repair work on the framed prefab building
is similar to the repair work on a standard frame
structure. Just keep in mind that this is a light frame
building. Repairs to the frame usually consist of nailing
splices beside the faulty member rather than attempting
to replace the frame.
4-26. Now that we have discussed wooden prefab
buildings, let's see how prefabricated metal buildings are
assembled and repaired.
5. Prefabricated Metal Buildings
5-1. The prefabricated metal buildings in use on
some military installations are constructed of many
different types of metal. However, galvanized sheet
metal and aluminum are the most common metals used
in prefab buildings. Most metal prefabs are referred to as
portable buildings, because they are easy to disassemble
Figure 31. Sill and joist assembly.