Asphalt and asbestos-cement roof coverings are most frequently used
on pitched-roof structures. Built-up
roofing is used mainly on flat or nearly flat roofs.
ASPHALT AND ASBESTOS-CEMENT ROOFING
Asphalt roofing comes in rolls (usually 3 feet wide) called rolled roofing,
in rolled strips (usually 15 inches wide and 3 feet long), and as individual
shingles. The type most commonly used is the flat strip, often called
A 1 x 3 square-butt shingle is shown in Figure 7-23. This shingle should
be laid 5 inches to the weather, meaning
that 7 inches of each course should be overlapped by the next higher course.
The lower, exposed end of a shingle is called the butt. The shingle shown
in Figure 7-23 has a square butt divided into three tabs. Various other
butt shapes are manufactured. Asbestos-cement roofing usually consists
of individual shingles.
Laying Asphalt Roofing
The first step in covering a
roof is to erect a scaffold to
a height which will bring
the eaves about waist-high
to a man standing on the
Before any roof covering is
applied, the roof sheathing
must be swept clean and
carefully inspected for
irregularities, cracks, holes,
or other defects. No roofing
should be applied unless
the sheathing boards are
An underlay of roofing felt is first applied to
the sheathing. Roofing felt usually comes in
3-foot-wide rolls and should be laid with a 2-
inch top lap and a 4-inch side lap.
Bundles of shingles should be distributed
along the scaffold before work begins. There
are 27 strips in a bundle of 1 x 3 asphalt
strip shingles. Three bundles will cover 100
After the first course at the eaves (the
starter course) is laid by inverting the first
course of shingles or the starter strip of
mineral-surfaced roll roofing, each course
that follows is begun by stretching a
guideline or by snapping a chalk line from
edge to edge. This positions the course.
Figure 7-24 shows the method of laying a 1 x 3 asphalt strip-shingle
roof. Strip shingles should be nailed with 1-inch copper or hot-dipped,
galvanized roofing nails, two to each tab; this means six nails to each
full strip. Nails should be placed about 6 1/2 inches from the butt edges
to ensure that each nail will be covered by the next course (blind-nailing)
and driven through two courses.
An asbestos-cement roof is laid in about the same way as the asphalt
Applying Shingles at Hips and Valleys
One side of a hip or valley shingle must be cut at an angle to obtain
an edge line that will match the line of the hip or valley rafter. One
way to cut these shingles is to use a pattern made as follows:
Select a piece of 1 x 6 material about 3 feet long. Determine the unit
length of a common rafter in the roof. Set the framing square back up
on the piece to the unit run of a common rafter on the tongue and the
unit length of a common rafter on the blade, as shown in Figure 7-25,
A. Draw a line along the tongue. Saw the piece along this line and use
it as a pattern to cut the shingles as shown in Figure 7-25, B.
Places especially susceptible to leakage in roofs and outside walls
are made watertight by the installation of flashing. Flashing is sheets
or strips of a watertight, rustproof material (such as galvanized sheet
or sheet copper alloy for valleys and felt for hips). Flashing deflects
water from places that are susceptible to leakage. The places in a roof
most subject to leakage are the lines along which adjoining roof surfaces
intersect (such as the lines followed by ridges, hips, and valleys) and
the lines of intersection between roof surfaces and the walls of dormers,
chimneys, skylights, and the like.
Ridge lines and hip lines naturally tend to shed water; therefore, they
are only moderately subject to leakage. A strip of felt paper usually
makes a satisfactory ridge or hip flashing. The ridge or hip is then finished
as shown in Figure 7-26. Squares are made by cutting shingles into thirds.
The squares are then blind-nailed to the ridge or hip as shown in Figure
Since water gathers in the roof valleys, they are more subject
to leakage. Valley flashing varies with the manner in which
the valley is to be finished. There are two common types of
valley finish: the open valley and the closed valley.
Figure 7-27 shows part of an open valley. The roof
covering does not extend across the valley. The flashing
consists of a prefabricated piece of galvanized iron,
copper, zinc, or similar metal, with a splash rib or ridge
down the center and a small crimp at the edges. The
flashing is nailed down to the valley, with nails driven in
the edges (outside the crimps), as shown in Figure 7-27.
Care must be taken not to drive nails through the
flashing inside the crimps, to avoid leakage. Figure 7-28,
page 7-18, shows an open valley using rolled roofing.
In the closed valley, the roof covering extends across the valley. Sheet
metal flashing is cut into
small sheets measuring
about 18 x 10 inches,
called shingle tins. This
flashing is laid under each
course of shingles, along the
valley, as the course is laid.
After the first course of the
double course at the eaves
is laid, the first sheet of
flashing is placed on top of
it. The second course is laid
over this one so that the
metal is partly covered by
the next course. This
procedure is continued all
the way up the valley.
Shingle tins measuring about 5 x 7
inches may also be used to lay flashing
up the side walls of dormers, chimneys,
skylights, and similar openings. Each tin
is bent at a right angle so that part of the
tin extends up the side wall and the rest
lies flat on the roof covering. This is
called side flashing. In addition to the
side flashing, a dormer, chimney, or
skylight has a strip of flashing called an
apron along the bottom of the outer wall
or face. A chimney or skylight has a
similar strip, called the saddle 1?ashing,
along the bottom of the inner wall or face.
Figure 7-29 shows vertical wall flashing.
BUILT-UP ROOFING MATERIAL
The following building papers are used on a built-up roof. Their purpose
is to prevent the seepage of bitumen through roof sheathing on which a
built-up roof has been applied.
· Rosin paper is a felt paper, usually pale red, filled with
· Kraft paper is a light brown paper that is usually glazed.
· Sisal kraft consists of two layers of glazed kraft paper with
a center section of sisal embedded in
a black bituminous compound and laminated by heat and pressure.
· Roofing felt is a felt paper that has been saturated with a bituminous
compound (heavy pitch or
asphalt oils). The basic
ingredients are usually either
asbestos or rag felts. The roll
may vary from 32 to 36 inches
wide. Weights for built-up
roofing vary from 15 to 65
pounds per square. The 15-
pound felt is most commonly
used because of its light
A binder is used to bond the roofing felt together and form a watertight
seal. Asphalt and coal tar are the two main types of bituminous binders
used. Drying out of the binder causes deterioration of built-up oofs.
If this did not happen, a built-up roof would last indefinitely. Asphalt
is the preferred binder. It is used on roofs sloping up to 6 inches per
foot (1/4 pitch). Asphalt has a melting point of 350' to 41 0°F. A
roof covered with asphalt should be protected with a covering of slag,
gravel, or other protective material. Tar has a lower melting point (300°
to 350°F) than asphalt, so it will move more easily; therefore, it
is not recommended for roofs having a slope of more than 3 inches per
foot (1/8 pitch).
Aggregate, crushed stone, or gravel from 1/4 to 5/8 inch in diameter
is embedded in a coat of asphalt or tar to hold the roof covering down.
It also prevents the binding from disintegrating because of the weather.
Gravel stops on slag or gravel-surfaced roofs, and metal-edge strips
on smooth-surfaced built-up roofs are used to finish all exposed edges
and eaves to prevent wind from getting under the edges and causing blowoffs.
The gravel stop also prevents the loss of gravel or slag off the edge
of the roof. The flashing flange of the gravel stop or edge strip is placed
over the last ply of felt. It should be nailed securely to the roof deck
and double felt stripped. Then the finished coat of bitumen and surfacing
or cap sheet should be applied. The lip of the gravel stop should extend
a minimum of 3/4 inch above the roof deck. The lip of the edge strip should
be a maximum of 1/2 inch above the deck. Both should be securely fastened
to the fascia board.