182 CHAPTER FOURTEEN
referred to as shakes.Lengths are 16, 18, and 24 to as long as 32
inches, but random widths of 4 to 12 inches are common.
Wood shingles are usually sold by the square based on a 10-
inch weather exposure. A double-starter course is usually
required; in some installations, roofing felt is also needed. Val-
leys will require some type of flashing, and hips and ridges
require extra material to cover the joint; thus extra-long nails
become requisite. Nails should be corrosion resistant, and 2 to
4 pounds of 1^3 ⁄ 4 - to 2-inch long nails are required per square.
14–12 Built-Up Roofing
Built-up roofingconsists of layers of overlapping roof felt
with each layer set in a mopping of hot tar or asphalt. Such
roofing is usually designated by the number of plies of felt
that are used; for example, a three-ply roof has four coats of
bituminous material (tar or asphalt) and three layers of felt.
Although built-up roofing is used primarily for flat and near-
flat roofs, it can be used on inclines of up to 9 inches per foot,
providing certain special bituminous products are used.
The specifications must be read carefully, because no one
type of system exists for all situations. There may be vapor
barrier requirements and varying amounts of lapping of felt.
Different weights and types of felts and bituminous materials
may be used. The deck that is to receive the roofing must be
considered, as must the service it is intended to sustain.
Many specifications require a bond on the roof. This
bond is furnished by the material manufacturer and sup-
plier through the roofing contractor. It generally guarantees
the water tightness of the installation for a period of 10, 15,
or 20 years. During this period of time, the manufacturer
will make repairs on the roof that become necessary due to
the normal wear and tear of the elements to maintain the
roof in a watertight condition. Each manufacturer has its
own specifications or limitations in regard to these bonds,
and the roofing manufacturer’s representative should be
called in for consultation. Special requirements may pertain
to approved roofers, approved flashing, and deck inspec-
tion; photographs may also be necessary. If it appears that the
installation may not be approved for bonding, the architect/
engineer should be so informed during the bid period. The
manufacturer’s representative should call on the architect/
engineer and explain the situation so that it can be worked
out before the proposals are due.
The takeoff follows the same general procedure as any
other roofing:
- The number of squares to be covered must be noted.
- Base sheets—a base sheet or vapor barrier is used, when
required; note the number of plies, lap (usually 4
inches), weight per ply per square. - Felt—determine the number of plies, weight of felt per
square, and type of bituminous impregnation (tar or
asphalt). - Bituminous material—note the type, number of coats,
and the pounds per coat per square (some specifications
call for an extra-heavy topcoat or pour).
5. Aggregate surface (if required)—the type and size of
slag, gravel, or other aggregate, and the pounds required
per square should all be noted.
6. Insulation (if required)—note type, thickness, and any
special requirements (refer also to Section 14–8).
7. Flashing—note type of material, thickness, width, and
linear feet required.
8. Trim—determine the type of material, size, shape and
color, method of attachment, and the linear footage
required.
9. Miscellaneous materials—blocking, cant strips, curbs,
roofing cements, nails and fasteners, caulking, and tap-
ing are some examples.
Bituminous materials are used to cement the layers of
felt into a continuous skin over the entire roof deck. Types of
bituminous material used are coal tar pitch and asphalts.
The specifications should indicate the amount of bitumi-
nous material to be used for each mopping so that each ply
of felt is fully cemented to the next. In no instance should felt
be allowed to touch felt. The mopping between felts averages
25 to 30 pounds per square, while the top pour (poured, not
mopped), which is often used, may be from 65 to 75 pounds
per square. It is this last pour into which any required aggre-
gate material will become embedded.
Felts are available in 15- and 30-pound weights, 36-inch
widths, and rolls 432 or 216 sf. With a 2-inch lap, a 432-sf
roll will cover 400 sf, while the 216-sf roll will cover 200 sf. In
built-up roofing, a starter strip 12 to 18 inches wide is
applied; then over that one, a strip 36 inches wide is placed.
The felts that are subsequently laid overlap the preceding
felts by 19, 24^2 ⁄ 3 , or 33 inches, depending on the number of
plies required. Special applications sometimes require other
layouts of felts. The specifications should be carefully
checked to determine exactly what is required as to weight,
starter courses, lapping, and plies. Waste averages about 8 to
10 percent of the required felt, which allows for the material
used for starter courses.
Aggregate surfaces such as slag or gravel are often
embedded in the extra-heavy top pouring on a built-up roof.
This aggregate acts to protect the membrane against the ele-
ments, such as hail, sleet, snow, and driving rain. It also pro-
vides weight against wind uplift. To ensure embedment in
the bituminous material, the aggregate should be applied
while the bituminous material is hot. The amount of aggre-
gate used varies from 250 to 500 pounds per square. The
amount required should be listed in the specifications. The
amount of aggregate required is estimated by the ton.
Since various types of materials may be used as aggre-
gates, the specifications must be checked for the size, type,
and gradation requirements. It is not unusual for aggregates
such as marble chips to be specified. This type of aggregate
will result in much higher material costs than gravel or slag.
Always read the specifications thoroughly.
The joints between certain types of roof deck materials—
such as precast concrete, gypsum, and wood fiber—may
be required to have caulking and taping of all joints. This