Mission Tile.— Mission tiles are slightly tapered
half-round units and are set in horizontal courses. The
convex and concave sides are alternated to form pans
and covers. The bottom edges of the covers can be laid
with a random exposure of 6 to 14 inches to weather.
Mission tile can be fastened to the prepared roof deck
with copper nails, copper wire, or specially designed
brass strips. The covers can be set in portland cement
mortar. This gives the roof a rustic appearance, but it
adds approximately 10 pounds per square to the weight
of the finished roof.
Flat Tile.— Flat tile can be obtained as either flat
shingle or interlocking. Single tiles are butted at the
sides and lapped shingle fashion. They are produced in
various widths from 5 to 8 inches with a textured surface
to resemble wood shingles, with smooth colored
surfaces, or with highly glazed surfaces. Interlocking
shingle tiles have side and top locks, which permit the
use of fewer pieces per square. The back of this type of
tile is ribbed. This reduces the weight without sacrificing
strength. Interlocking flat tile can be used in
combination with lines of Greek pan-and-cover tile as
accents.
Concrete.— The acceptance of concrete tile as a
roofing material has been slow in the United States.
However, European manufacturers have invested
heavily in research and development to produce a
uniformly high-quality product at a reasonable cost.
Concrete tile is now used on more than 80 percent of all
new residences in Great Britain. Modern high-speed
machinery and techniques have revolutionized the
industry in the United States, and American-made
concrete tiles are now finding a wide market,
particularly in the West.
Concrete roof tile, made of Portland cement, sand,
and water, is incombustible. It is also a poor conductor
of heat. These characteristics make it an ideal roofing
material in forested or brushy areas subject to periodic
threats of fire. In addition, concrete actually gains
strength with age and is unaffected by repeated freezing
and thawing cycles.
Color pigments may be mixed with the basic
ingredients during manufacture. To provide a glazed
surface, cementitious mineral-oxide pigments are
sprayed on the tile immediately after it is extruded. This
glaze becomes an integral part of the tile. The surface of
these tiles may be scored to give the appearance of rustic
wood shakes.
Most concrete tiles are formed with side laps
consisting of a series of interlocking ribs and grooves.
These are designed to restrict lateral movement and
provide weather checks between the tiles. The underside
of the tile usually contains weather checks to halt
wind-blown water. Head locks, in the form of lugs,
overlap wood battens roiled to solid sheathing or strips
of spaced sheathing. Nail holes are prepunched The
most common size of concrete tile is 123/8 by 17 inches.
This provides for maximum coverage with minimum
lapping,
Concrete tiles are designed for minimum roof
slopes of 2 1/2:12. For slopes up to 3 1/2:12, roof decks
are solidly sheeted and covered with roofing felt. For
slopes greater than 3 1/2:12, the roof sheathing can be
spaced. Roofing felt is placed between each row to carry
any drainage to the surface of the next lower course of
tile. The lugs at the top of the tiles lock over the
sheathing or stripping. Generally, only every fourth tile
in every fourth row is nailed to the sheathing, except
where roofs are exposed to extreme winds or earthquake
conditions. The weight of the tile holds it in place.
Lightweight concrete tile is now being produced
using fiberglass reinforcing and a lightweight perlite
aggregate. These tiles come in several colors and have
the appearance of heavy cedar shakes. The weight of
these shingles is similar to that of natural cedar shakes,
so roof reinforcing is usually unnecessary.
SLATE.— Slate roofing is hand split from natural
rock. It varies in color from black through blue-gray,
gray, purple, red and green. The individual slates may
have one or more darker streaks running across them.
These are usually covered during the laying of the slate.
Most slate rooting is available in sizes from 10 by 6 to
26 by 14 inches. The standard thickness is 3/16 inch, but
thicknesses of 1/4, 3/8, 1/2, and up to 2 inches can be
obtained. Slate may be furnished in a uniform size or in
random widths. The surface may be left with the rough
hand-split texture or ground to a smoother texture.
The weight of a slate roof ranges from 700 to 1,500
pounds per square, depending upon thickness. The size
of framing members supporting a slate roof must be
checked against the weight of the slate and method of
laying. The type of underpayment used for a slate roof
varies, depending on local codes. The requirement
ranges from one layer of 15-pound asphalt-saturated felt
to 65-pound rolled asphalt roofing for slate over 3/4 inch
thick.
Slate is usually laid like shingles with each course
lapping the second course below at least 3 inches. The
slates can be laid in even rows or at random. Each slate
is predrilled with two nail holes and is held in place with
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