ROOFING TERMS AND MATERIALS
Upon completing this section, you should be able to define roofing terms and identify roofing materials.
The roof covering, or roofing, is a part of the exterior finish. It should provide long-lived waterproof protection for the building and its contents from rain, snow, wind, and, to some extent, heat and cold.
Before we begin our discussion of roof coverings, lets first look at some of the mast common terms used in roof construction.
Correct use of roofing terms is not only the mark of a good worker, but also a necessity for good construction. This section covers some of the more common roofing terms you need to know.
Square. Roofing is estimated and sold by the square. A square of roofing is the amount required to cover 100 square feet of the roof surface.
Coverage. Coverage is the amount of weather protection provided by the overlapping of shingles. Depending on the kind of shingle and method of application, shingles may furnish one (single coverage), two (double coverage), or three (triple coverage) thicknesses of material over the roof surface. Shingles providing single coverage are suitable for re-roofing over existing roofs. Shingles providing double and triple coverage are used for new construction. Multiple coverage increases weather resistance and provides a longer service life.
Shingle Surfaces. The various surfaces of a shingle are shown in view A of figure 3-13. "Shingle width" refers to the total measurement across the top of either a strip type or individual type of shingle. The area that one shingle overlaps a shingle in the course (row) below it is referred to as "top lap." "Side lap" is the area that one shingle overlaps a shingle next to it in the same course. The area that one shingle overlaps a shingle two courses below it is known as head lap. Head lap is measured from the bottom edge of an overlapping shingle to the nearest top edge of an overlapped shingle. "Exposure" is the area that is exposed (not overlapped) in a shingle. For the best protection against leakage, shingles (or shakes) should be applied only on roofs with a unit rise of 4 inches or more. A lesser slope creates slower water runoff, which increases the possibility of leakage as a result of windblown rain or snow being driven underneath the butt ends of the shingles.
Figure 3-13.-Roofing terminology: A. Surfaces; B. Slope and pitch.
Slope. "Slope" and "pitch" are often incorrectly used synonymously when referring to the incline of a sloped roof. View B of figure 3-13 shows some common roof slopes with their corresponding roof pitches.
"Slope" refers to the incline of a roof as a ratio of vertical rise to horizontal run. It is expressed sometimes as a fraction but typically as X-in-12; for example, a 4-in-12 slope for a roof that rises at the rate of 4 inches for each foot (12 inches) of run. The triangular symbol above the roof in figure 3-13, view B, conveys this information.
Pitch. "Pitch" is the incline of a roof as a ratio of the vertical rise to twice the horizontal run. It is expressed as a fraction. For example, if the rise of a roof is 4 feet and the run 12 feet, the roof is designated as having a pitch of 1/6 (4/24= 1/6).
In completing roofing projects, you will be working with a number of different materials. In the following section, we will discuss the most common types of underlayments, flashing, roofing cements, and exterior materials you will encounter. We will also talk about built-up roofing.
Materials used for pitched roofs include shingles of asphalt, fiberglass, and wood. Shingles add color, texture, and pattern to the roof surface. To shed water, all shingles are applied to roof surfaces in some overlapping fashion. They are suitable for any roof with enough slope to ensure good drainage. Tile and date are also popular. Sheet materials, such as roll roofing,
galvanized steel, aluminum, copper, and tin, are sometimes used. For flat or low-pitched roofs, composition or built-up roofing with a gravel topping or cap sheet are frequent combinations. Built-up roofing consists of a number of layers of asphalt-saturated felt mopped down with hot asphalt or tar. Metal roofs are sometimes used on flat decks of dormers, porches, or entryways.
The choice of materials and the method of application are influenced by cost, roof slope, expected service life of the roofing, wind resistance, fire resistance, and local climate. Because of the large amount of exposed surface of pitched roofs, appearance is also important.
There are basically four types of underlayments you will be working with as a Builder: asphalt felt, organic, glass fiber, and tarred.
Once the roof sheathing is in place, it is covered with an asphalt felt underpayment commonly called roofing felt. Roofing felt is asphalt-saturated and serves three basic purposes. First, it keeps the roof sheathing dry until the shingles can be applied. Second, after the shingles have been laid, it acts as a secondary barrier against wind-driven rain and snow. Finally, it also protects the shingles from any resinous materials, which could be released from the sheathing.
Roofing felt is designated by the weight per square. As we mentioned earlier, a square is equal to 100 square feet and is the common unit to describe the amount of roofing material. Roofing felt is commonly available in rolls of 15 and 30 pounds per square. The rolls are usually 36 inches wide. A roll of 15-pound felt is 144 feet long, whereas a roll of 30-pound felt is 72 feet long. After you allow for a 2-inch top lap, a roll of 15-pound felt will cover 4 squares; a roll of 30-pound felt will cover 2 squares.
Underpayment should be a material with low vapor resistance, such as asphalt-saturated felt. Do not use materials, such as coated felts or laminated waterproof papers, which act as a vapor barrier. These allow moisture or frost to accumulate between the underlayment and the roof sheathing. Underlayment requirements for different kinds of shingles and various roof slopes are shown in table 3-5.
Table 3-5.-Underlayment Recommendations for Shingle Roofs
Apply the underpayment as soon as the roof sheathing has been completed. For single underpayment, start at the cave line with the 15-pound felt. Roll across the roof with atop lap of at least 2 inches at all horizontal points and a 4-inch side lap at all end joints (fig. 3-14, view A). Lap the underlayment over all hips and ridges 6 inches on each side. A double underpayment can be started with two layers at the cave line, flush with the fascia board or molding. The second and remaining strips have 19-inch head laps with 17-inch exposures (fig. 3-14, view B). Cover the entire roof in this manner. Make sure that all surfaces have double coverage. Use only enough fasteners to hold the underpayment in place until the shingles are applied. Do not apply shingles over wet underpayment.
Figure 3-14.-Roofing underlayment: A. Single coverage; B. Double coverage.
In areas where moderate-to-severe snowfall is common and ice dams occur, melting snow refreezes at the cave line (fig. 3-15, view A). It is a good practice to apply one course of 55-pound smooth-surface roll roofing as a flashing at the eaves. It should be wide enough to extend from the roof edge to between 12 and 24 inches inside the wall line. The roll roofing should be installed over the underpayment and metal drip edge. This will lessen the chance of melting snow to back up under the shingles and fascia board of closed cornices. Damage to interior ceilings and walls results from this water seepage. Protection from ice dams is provided by cave flashing. Cornice ventilation by means of soffit vents and sufficient insulation will minimize the melting (fig. 3-15, view B).
Figure 3-15.-Protection from ice dams A. Refreezing snow and ice; B. Cornice ventilation.
ASPHALT FELT. Roofing felts are used as underpayment for shingles, for sheathing paper, and for reinforcements in the construction of built-up roofs. They are made from a combination of shredded wood fibers, mineral fibers, or glass fibers saturated with asphalt or coal-tar pitch. Sheets are usually 36 inches wide and available in various weights from 10 to 50 pounds. These weights refer to weight per square (100 feet).
ORGANIC FELTS. Asphalt-saturated felts composed of a combination of felted papers and organic shredded wood fibers are considered felts. They are among the least expensive of roofing felts and are widely used not only as roofing, but also as water and vapor retarders. Fifteen-pound felt is used under wood siding and exterior plaster to protect sheathing or wood studs. It is generally used in roofing for layers or plies in gravel-surfaced assemblies and is available perforated. Perforated felts used in built-up roofs allow entrapped moisture to escape during application. Thirty-pound felt requires fewer layers in a built-up roof. It is usually used as underlayment for heavier cap sheets or tile on steeper roofs.
GLASS-FIBER FELTS. Sheets of glass fiber, when coated with asphalt, retain a high degree of porosity, assuring a maximum escape of entrapped moisture or vapor during application and maximum bond between felts. Melted asphalt is applied so that the finished built-up roof becomes a monolithic slab reinforced with properly placed layers of glass fibers. The glass fibers, which are inorganic and do not curl, help create a solid mass of reinforced waterproof rooting material.
TARRED FELTS. Coal-tar pitch saturated organic felts are available for use with bitumens of the same composition. Since coal-tar and asphalt are not compatible, the components in any construction must be limited to one bitumen or the other unless approved by the felt manufacturer.
The roof edges along the eaves and rake should have a metal drip edge, or flashing. Flashing is specially constructed pieces of sheet metal or other materials used to protect the building from water seepage. Flashing must be made watertight and be water shedding. Flashing materials used on roofs may be asphalt-saturated felt, metal, or plastic. Felt flashing is generally used at the ridges, hips, and valleys. However, metal flashing, made of aluminum, galvanized steel, or copper, is considered superior to felt. Metal used for flashing must be corrosion resistant. It should be galvanized steel (at least 26 gauge), 0.019-inch-thick aluminum, or 16-ounce copper.
Flashing is available in various shapes (fig. 3-16, view A), formed from 26-gauge galvanized steel. It should extend back approximately 3 inches from the roof edge and bend downward over the edge. This causes the water to drip free of underlying cornice construction. At the eaves, the underpayment should be laid over the drip edge (view B). At the rake (view C), place the underpayment under the drip edge. Galvanized nails, spaced 8 to 10 inches apart, are recommended for fastening the drip edge to the sheathing.
Figure 3-16.-Drip edges A. Basic shapes B. At the eave; C. At the rake.
The shape and construction of different types of roofs can create different types of water leakage problems. Water leakage can be prevented by placing flashing materials in and around the vulnerable areas of the roof. These areas include the point of intersection between roof and soil stack or ventilator, the valley of a roof, around chimneys, and at the point where a wall intersects a roof.
As you approach a soil stack, apply the roofing up to the stack and cut it to fit (fig. 3-17). You then install a corrosion-resistant metal sleeve, which slips over the stack and has an adjustable flange to fit the slope of the roof. Continue shingling over the flange. Cut the shingles to fit around the stack and press them firmly into the cement.
Figure 3-17.-Flashing around a roof projection.
The open or closed method can be used to construct valley flashing. A valley underpayment strip of 15-pound asphalt- saturated felt, 36 inches wide, is applied first. The strip is centered in the valley and secured with enough nails to hold it in place. The horizontal courses of underlayment are cut to overlap this valley strip a minimum of 6 inches.
Open valleys can be flashed with metal or with 90-pound mineral-surfaced asphalt roll roofing. The color can match or contrast with the roof shingles. An 18-inch-wide strip of mineral-surfaced roll rooting is placed over the valley underpayment. It is centered in the valley with the surfaced side down and the lower edge cut to conform to and be flush with the cave flashing. When it is necessary to splice the material, the ends of the upper segments are laid to overlap the lower segments 12 inches and are secured with asphalt plastic cement. This method is shown in figure 3-18. Only enough nails are used 1 inch in from each edge to hold the strip smoothly in place.
Another 36-inch-wide strip is placed over the first strip. It is centered in the valley with the surfaced side up and secured with nails. It is lapped the same way as the underlying 18-inch strip.
Before shingles are applied, a chalk line is snapped on each side of the valley. These lines should start 6 inches apart at the ridge and spread wider apart (at the rate of 1/8 inch per foot) to the eave (fig. 3-18). The chalk lines serve as a guide in trimming the shingle units to fit the valley and ensure a clean, sharp edge. The upper corner of each end shingle is clipped to direct water into the valley and prevent water penetration between courses. Each shingle is cemented to the valley lining with asphalt cement to ensure a tight seal. No exposed nails should appear along the valley flashing.
Figure 3-18.-Open valley flashing using roll roofing.
Closed (woven) valleys can be used only with strip shingles. This method has the advantage of doubling the coverage of the shingles throughout the length of the valley. This increases the weather resistance at this vulnerable point. A valley lining made from a 36-inch-wide strip of 55-pound (or heavier) roll roofing is placed over the valley underpayment and centered in the valley (fig. 3-19).
Figure 3-19.-Closed valley flashing.
Valley shingles are laid over the lining by either of two methods:
- They can be applied on both roof surfaces at the same time with each course, in turn, woven over the valley.
- Each surface can be covered to the point approximately 36 inches from the center of the valley and the valley shingles woven in place later.
In either case, the first course at the valley is laid along the eaves of one surface over the valley lining and extended along the adjoining roof surface for a distance of at least 12 inches. The first course of the adjoining roof surface is then carried over the valley on top of the previously applied shingle. Succeeding courses are then laid alternately, weaving the valley shingles over each other.
The shingles are pressed tightly into the valley and nailed in the usual manner. No nail should be located closer than 6 inches to the valley center line, and two nails should be used at the end of each terminal strip.
As you approach a chimney, apply the shingles over the felt up to the chimney face. If 90-pound roll roofing is to be used for flashing, cut wood cant strips and install them above and at the sides of the chimney (fig. 3-20). The roll roofing flashing should be cut to run 10 inches up the chimney. Working from the bottom up, fit metal counterflashing over the base flashing and insert it 1 1/2 inches into the mortar joints. Refill the joints with mortar or roofing cement. The counterflashing can also be installed when the chimney masonry work is done,
Figure 3-20.-Flashing around a chimney.
Where the roof intersects a vertical wall, it is best to install metal flashing shingles. They should be 10 inches long and 2 inches wider than the exposed face of the regular shingles. The 10-inch length is bent so that it will extend 5 inches over the roof and 5 inches up the wall (see figure 3-21). Apply metal flashing with each course. This waterproofs the joint between a sloping roof and vertical wall. This is generally called step flashing.
As each course of shingles is laid, a metal flashing shingle is installed and nailed at the top edge as shown. Do not nail flashing to the wall; settling of the roof frame could damage the seal.
Wall siding is installed after the roof is completed. It also serves as a cap flashing. Position the siding just above the roof surface. Allow enough clearance to paint the lower edges.
Roofing cements are used for installing cave flashing, for flashing assemblies, for cementing tabs of asphalt shingles and laps in sheet material, and for repairing roofs. There are several types of cement, including plastic asphalt cements, lap cements, quick-setting asphalt adhesives, roof coatings, and primers. The type and quality of materials and methods of application on a shingle roof should follow the recommendation of the manufacturer of the shingle roofing.
Basically, exterior roof treatment consists of applying various products, including shingles, roll roofing, tiles, slate, and bituminous coverings. Treatment also includes specific construction considerations for ridges, hips, and valleys.
SHINGLES. The two most common shingle types are asphalt and fiberglass, both of which come in various strip shapes.
Asphalt. Asphalt (composition) shingles are available in several patterns. They come in strip form or as individual shingles. The shingles are manufactured on a base of organic felt (cellulose) or an inorganic glass mat. The felt or mat is covered with a mineral-stabilized coating of asphalt on the top and bottom. The top side is coated with mineral granules of specified color. The bottom side is covered with sand, talc, or mica.
Fiberglass. Improved technologies have made the fiberglass mat competitive with organic felt. The weight and thickness of a fiberglass mat is usually less than that of organic felt. A glass fiber mat maybe 0.030 inch thick versus 0.055 inch thick for felt. The popularity of fiberglass-based shingles is their low cost. The mat does not have to be saturated in asphalt. ASTM standards specify 3 pounds per 100 feet. The combination of glass fiber mats with recently developed resins has significantly lowered the price of composition shingles.
Strip. One of the most common shapes of asphalt or fiberglass shingles is a 12- by 36-inch strip (fig. 3-22) with the exposed surface cut or scored to resemble three 9-by 12-2- inch shingles. These are called strip shingles. They are usually laid with 5 inches exposed to the weather. A lap of 2 to 3 inches is usually provided over the upper edge of the shingle in the course directly below. This is called the head lap.
Figure 3-22.-A typical 12- by 36-inch shingle.
The thickness of asphalt shingles may be uniform throughout, or, as with laminated shingles, slotted at the butts to give the illusion of individual units. Strip shingles are produced with either straight-tab or random-tab design to give the illusion of individual units or to simulate the appearance of wood shakes. Most strip shingles have factory-applied adhesive spaced at intervals along the concealed portion of the strip. These strips of adhesive are activated by the warmth of the sun and hold the shingles firm through wind, rain, and snow.
Strip shingles are usually laid over a single thickness of asphalt-saturated felt if the slope of the roof is 4:12 or greater. When special application methods are used, organic- or inorganic-base-saturated or coated-strip shingles can be applied to decks having a slope of 4:12, but not less than 2:12. Figure 3-23 shows the application of shingles over a double layer of underpayment. Double underpayment is recommended under square-tab strip shingles for slopes less than 4:12.
Figure 3-23.-Special shingle application.
When roofing materials are delivered to the building site, they should be handled with care and protected from damage. Try to avoid handling asphalt shingles in extreme heat or cold. They are available in one-third-square bundles, 27 strip shingles per bundle. Bundles should be stored flat so the strips will not curl after the bundles are open. To get the best performance from any roofing material, always study the manufacturers directions and install as directed.
On small roofs (up to 30 feet long), strip shingles can be laid starting at either end. When the roof surface is over 30 feet long, it is usually best to start at the center and work both ways. Start from a chalk line perpendicular to the eaves and ridge.
Asphalt shingles will vary slightly in length (plus or minus 1/4 inch in a 36-inch strip). There may also be some variations in width. Thus, chalk lines are required to achieve the proper horizontal and vertical placement of the shingles (fig. 3-24).
Figure 3-24.-Laying out a shingle roof.
The first chalk line from the cave should allow for the starter strip and/or the first course of shingles to overhang the drip edge 1/4 to 3/8 inch.
When laying shingles from the center of the roof toward the ends, snap a number of chalk lines between the eaves and ridge. These lines will serve as reference marks for starting each course. Space them according to the shingle type and laying pattern.
Chalk lines, parallel to the eaves and ridge, will help maintain straight horizontal lines along the butt edge of the shingle. Usually, only about every fifth course needs to be checked if the shingles are skillfully applied. Inexperienced workers may need to set up chalk lines for every second course.
The purpose of a starter strip is to back up the first course of shingles and fill in the space between the tabs. Use a strip of mineral-surfaced roofing 9 inches or wider of a weight and color to match the shingles. Apply the strip so it overhangs the drip edge 1/4 to 3/8 inch above the edge. Space the nails so they will not be exposed at the cutouts between the tabs of the first course of shingles. Sometimes an inverted (tabs to ridge) row of shingles is used instead of the starter strip. When you are laying self-sealing strip shingles in windy areas, the starter strip is often formed by cutting off the tabs of the shingles being used. These units are then nailed in place, right side up, and provide adhesive under the tabs of the first course.
Nails used to apply asphalt roofing must have a large head (3/8- to 7/1 6-inch diameter) and a sharp point. Figure 3-25 shows standard nail designs (view A) and recommended lengths (view B) for nominal 1-inch sheathing. Most manufacturers recommend 12-gauge galvanized steel nails with barbed shanks. Aluminum nails are also used. The length should be sufficient to penetrate the full thickness of the sheathing or 3/4 inch into the wood.
| || |
|1" Sheating || |
|Strip or individual shingle (new construction) ||1¼" ||7/8" |
|Over asphalt roofing (reroofing) ||1½" ||1" |
|Over wood shingles (reroofing) ||1¾" ||-- |
Figure 3-25.-Nails suitable for installing strip shingles, recommended nail lengths, and nail placement.
The number of nails and correct placement are both vital factors in proper application of rooting material. For three-tab square-butt shingles, use a minimum of four nails per strip (fig. 3-25, view C). Specifications may require six nails per shingle (view C). Align each shingle carefully and start the nailing from the end next to the one previously laid. Proceed across the shingle. This will prevent buckling. Drive nails straight so that the edge of the head will not cut into the shingle. The nail head should be driven flush, not sunk into the surface. If, for some reason, the nail fails to hit solid sheathing, drive another nail in a slightly different location.
WOOD SHINGLES AND SHAKES. Wood shingles are available in three standard lengths: 16, 18, and 24 inches. The 16-inch length is the most popular. It has five-butt thicknesses per 2 inches of width when it is green (designated a 5/2). These shingles are packed in bundles. Four bundles will cover 100 square feet of wall or roof with 5-inch exposure. The 18- or 24-inch-long shingles have thicker butts-five in 2 1/4 inches for the 18-inch shingles and four in 2 inches for 24-inch shingles. The recommended exposures for the standard wood-shingle size are shown in table 3-6.
Table 3-6.-Recommended Exposure for Wood Shingles
Figure 3-26 shows the proper method of applying a wood-shingle roof. Underpayment or roofing felt is not required for wood shingles except for protection in ice jam areas. Although spaced or solid sheathing is optional, spaced roof sheathing under wood shingles is most common. Observe the following steps when applying wood shingles:
Figure 3-26.-Installation of wood shingles.
- Extend the shingles 1 1/2 inches beyond the cave line and 3/4 inch beyond the rake (gable) edge.
- Use two rust-resistant nails in each shingle. Space them 3/4 inch from the edge and 1 1/2 inches above the butt line of the next course.
- Double the first course of shingles. In all courses, allow 1/8- to 1/4-inch space between each shingle for expansion when they are wet. Offset the joints between the shingles at least 1 1/2 inches from the joints in the course below. In addition, space the joints in succeeding courses so that they do not directly line up with joints in the second course below.
- Where valleys are present, shingle away from them. Select and precut wide valley shingles.
- Use metal edging along the gable end to aid in guiding the water away from the sidewalls.
- Use care when nailing wood shingles. Drive the nails just flush with the surface. The wood in shingles is soft and can be easily crushed and damaged under the nail heads.
Wood shakes are usually available in several types, but the split-and-resawed type is the most popular. The sawed face is used as the back face and is laid flat on the roof. The butt thickness of each shake ranges between 3/4 inch and 1 1/2 inches. They are usually packed in bundles of 20 square feet with five bundles to the square.
Wood shakes are applied in much the same way as wood shingles. Because shakes are much thicker (longer shakes have the thicker butts), use long galvanized nails. To create a rustic appearance, lay the butts unevenly. Because shakes are longer than shingles, they have greater exposure. Exposure distance is usually 7 1/2 inches for 18-inch shakes, 10 inches for 24-inch shakes, and 13 inches for 32-inch shakes. Shakes are not smooth on both faces, and because wind-driven rain or snow might enter, it is essential to use an underpayment between each course. A layer of felt should be used between each course with the bottom edge positioned above the butt edge of the shakes a distance equal to double the weather exposure. A 36-inch-wide strip of the asphalt felt is used at the cave line. Solid sheathing should be used when wood shakes are used for roofs in areas where wind-driven snow is common.
ROLL ROOFING. Roll roofing is made of an organic or inorganic felt saturated with an asphalt coating and has a viscous bituminous coating. Finely ground talc or mica can be applied to both sides of the saturated felt to produce a smooth roofing. Mineral granules in a variety of colors are rolled into the upper surface while the final coating is still soft. These mineral granules protect the underlying bitumen from the deteriorating effects of sun rays. The mineral aggregates are nonflammable and increase the fire resistance and improve the appearance of the underlying bitumen. Mineral-surfaced roll roofing comes in weights of 75 to 90 pounds per square. Roll roofing may have one surface completely covered with granules or have a 2-inch plain-surface salvage along one side to allow for laps.
Roll roofing can be installed by either exposed or concealed nailing. Exposed nailing is the cheapest but doesnt last as long. This method uses a 2-inch lap at the side and ends. It is cemented with special cement and nailed with large-headed nails. In concealed-nailing installations, the roll roofing is nailed along the top of the strip and cemented with lap cement on the bottom edge. Vertical joints in the roofing are cemented into place after the upper edge is nailed. This method is used when maximum service life is required.
Double-coverage roll roofing is produced with slightly more than half its surface covered with granules. This roofing is also known as 19-inch salvage edge. It is applied by nailing and cementing with special adhesives or hot asphalt. Each sheet is lapped 19 inches, blind-nailed in the lapped salvage portion, and then cemented to the sheet below. End laps are cemented into place.
TILES. Roofing tile was originally a thin, solid unit made by shaping moist clay in molds and drying it in the sun or in a kiln. Gradually, the term has come to include a variety of tile-shaped units made of clay, Portland cement, and other materials. Tile designs have come down to us relatively unchanged from the Greeks and Remans. Roofing tiles are durable, attractive, and resistant to fire; however, because of their weight (table 3-7), they usually require additional structural framing members and heavier roof decks.
Table 3-7.-Weight of Roofing Materials
Clay. The clays used in the manufacture of roofing tile are similar to those used for brick. Unglazed tile comes in a variety of shades, from a yellow-orange to a deep red, and in blends of grays and greens. Highly glazed tiles are often used on prominent buildings and for landmark purposes.
Clay roofing tiles are produced as either flat or roll tile. Flat tile may be English (interlocking shingle) or French. Roll tiles are produced in Greek or Roman pan-and-cover, Spanish or Mission style (fig. 3-27).
Roll Tile. Roll tile is usually installed over two layers of hot-mopped 15-pound felt. Double-coverage felts, laid shingle fashion, lapped 19 inches, and mopped with hot asphalt, may be required as an underpayment. The individual tiles are nailed to the sheathing through prepunched holes. Special shapes are available for starter courses, rakes, hips, and ridges. Some manufacturers produce tiles in special tile-and-a-half units for exposed locations, such as gables and hips.
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.
Figure 3-27.-Types of clay roof tiles.
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 two large-headed slaters nails. These are made of hard copper wire, cut copper, or cut brass. On hips, ridges, and in other locations where nailing is not possible, the slates are held in place with waterproof elastic slaters cement colored to match the slate. Exposed nail heads are covered with the same cement.
BITUMENS. Hot bituminous compounds (bitumens) are used with several types of roofing systems. Both asphalt and coal-tar pitch are bitumens. Although these two materials are similar in appearance, they have different characteristics. Asphalt is usually a product of the distillation of petroleum, whereas coal-tar pitch is a byproduct of the coking process in the manufacture of steel.
Some asphalts are naturally occurring or are found in combination with porous rock. However, most roofing asphalts are manufactured from petroleum crudes from which the lighter fractions have been removed. Roofing asphalts are available in a number of different grades for different roof slopes, climatic conditions, or installation methods.
Roofing asphalts are graded on the basis of their softening points, which range from a low of 135°F (57.2°C) to a high of 225°F (107.2°C). The softening point is not the point at which the asphalt begins to flow, but is determined by test procedures established by the ASTM. Asphalts begin to flow at somewhat lower temperatures than their softening points, depending on the slope involved and the weight of the asphalt and surfacing material.
Generally, the lower the softening point of an asphalt, the better its self-healing properties and the less tendency it has to crack. Dead-flat roofs, where water may stand, or nearly flat roofs, require an asphalt that has the greatest waterproofing qualities and the self-healing properties of low-softening asphalts. A special asphalt known as dead-flat asphalt is used in such cases. As the slope of the roof increases, the need for waterproofing is lessened, and an asphalt that will not flow at expected normal temperatures must be used. For steeper roofing surfaces, asphalt with a softening point of 185°F to 205°F (85°C to 96.1°C) is used. This material is classed as steep asphalt. In hot, dry climates only the high-temperature asphalts can be used.
The softening point of coal-tar pitch generally ranges from 140°F to 155°F (60.0°C to 68.3°C). The softening point of coal-tar pitch limits its usefulness; however, it has been used successfully for years in the eastern and middle western parts of the United States on dead-level or nearly level roofs. In the southwest, where roof surfaces often reach temperatures of 126°F to 147°F (52.2°C to 63.9°C) in the hot desert sun, the low-softening point of coal-tar pitch makes it unsuitable as a roof surfacing material.
When used within its limitations on flat and low-pitched roofs in suitable climates, coal-tar pitch provides one of the most durable roofing membranes. Coal-tar pitch is also reputed to have cold-flow, or self-healing, qualities. This is because the molecular structure of pitch is such that individual molecules have a physical attraction for each other, so self-sealing is not dependent on heat. Coal-tar pitch roofs are entirely unaffected by water. When covered by mineral aggregate, standing water may actually protect the volatile oils.
CONSTRUCTION CONSIDERATIONS. Laying rooting on a flat surface is a relatively easy procedure. Correctly applying materials to irregular surfaces, such as ridges, hips, and valleys, is somewhat more complex.
Ridge. The most common type of ridge and hip finish for wood and asphalt shingles is the Boston ridge. Asphalt-shingle squares (one-third of a 12- by 36-inch strip) are used over the ridge and blind-nailed (fig. 3-28, view A). Each shingle is lapped 5 to 6 inches to give double coverage. In areas where driving rains occur, use metal flashing under the shingle ridge to help prevent seepage. The use of a ribbon of asphalt roofing cement under each lap will also help.
A wood-shingle roof should be finished with a Boston ridge (fig. 3-28, view B). Shingles, 6 inches wide, are altemately lapped, fitted, and blind-nailed. As shown, the shingles are nailed in place so that the exposed trimmed edges are alternately lapped. Reassembled hip and ridge units for wood-shingle roofs are available and save both time and money.
Figure 3-28.-Finish at the ridge: A. Boston ridge with strip shingles; B. Boston ridge with wood shingles; C. Metal ridge.
A metal ridge can also be used on asphalt-shingle or wood-shingle roofs (fig. 3-28, view C). This ridge is formed to the roof slope and should be copper, galvanized iron, or aluminum. Some metal ridges are formed so that they provide an outlet ventilating area. However, the design should be such that it prevents rain or snow from blowing in.
Hips and Valleys. One side of a hip or valley shingle must be cut at an angle to obtain an edge that will match the line of the hip or valley rafter. One way to cut these shingles is to use a pattern. First, select a 3 foot long 1 by 6. Determine the unit length of a common rafter in the roof (if you do not already know it). Set the framing square on the piece to get the unit run of the common rafter on the blade and the unit rise of the common rafter on the tongue (fig. 3-29). Draw a line along the tongue; then saw the pattern along this line. Note: The line cannot be used as a pattern to cut a hip or valley.
Figure 3-29.-Layout pattern for hip and valley shingles.
A built-up roof, as the name indicates, is built up in alternate plies of roofing felt and bitumen. The bitumen forms a seamless, waterproof, flexible membrane that conforms to the surface of the roof deck and protects all angles formed by the roof deck and projecting surfaces, Without the reinforcement of the felts, the bitumens would crack and alligator and thus lose their volatile oils under solar radiation.
APPLICATION OF BITUMENS.The method of applying roofing depends on the type of roof deck. Some roof decks are nailable and others are not. Figure 3-30 shows examples of wood deck (nailable), concrete deck (not nailable), and built-up roof over insulation. Nailable decks include such materials as wood or fiberboard, poured or precast units of gypsum, and nail able lightweight concrete. Non-nailable decks of concrete or steel require different techniques of roofing. View A of figure 3-30 shows a three-ply built-up roof over a nailable deck, with a gravel or slag surface. View B shows a three-ply built-up roof over a nonnailable deck with a gravel or slag surface. View C shows a four-ply built-up roof over insulation, with a gravel or slag surface.
Figure 3-30.-Types of built-up roofing.
The temperatures at which bitumens are applied are very critical. At high temperatures, asphalt is seriously damaged and its life considerably shortened. Heating asphalt to over 500°F (260°C) for a prolonged period may decrease the weather life by as much as 50 percent. Coal-tar pitch should not be heated above 400°F (204°C). Asphalt should be applied to the roof at an approximate temperature of 375°F to 425°F (190.6°C to 218.3°C), and coal-tar pitch should be applied at 275°F to 375°F (135°C to 190°C).
Bitumens are spread between felts at rates of 25 to 35 pounds per square, depending on the type of ply or roofing felt. An asphalt primer must be used over concrete before the hot asphalt is applied. It usually is unnecessary to apply a primer under coal-tar pitch. With wood and other types of nailable decks, the ply is nailed to the deck to seal the joints between the units and prevent dripping of the bitumens through the deck.
Built-up roofs are classed by the number of plies of felt that is used in their construction. The roof maybe three-ply, four-ply, or five-ply, depending on whether the roofing material can be nailed to the deck whether insulation is to be applied underneath it, the type of surfacing desired, the slope of the deck, the climatic conditions, and the life expectancy of the roofing.
The ply-and-bitumen membrane of a built-up roof must form a flexible covering that has sufficient strength to withstand normal structure expansion. Most built-up roofs have a surfacing over the last felt ply. This protective surfacing can be applied in several ways.
SURFACING.Glaze-coat and gravel surfaces are the most commonly seen bituminous roofs.
Glaze Coat.A coat of asphalt can be flooded over the top layer of felt. This glaze coat protects the top layer of felt from the rays of the sun. The glaze coat is black, but it maybe coated with white or aluminum surfacing to provide a reflective surface.
Gravel.A flood coat of bitumen (60 pounds of asphalt or 70 pounds of coal-tar pitch per square) is applied over the top ply. Then a layer of aggregate, such as rock gravel, slag, or ceramic granules, is applied while the flood coat is still hot. The gravel weighs approximately 400 pounds per square and the slag 325 pounds per square. Other aggregates would be applied at a rate consistent with their weight and opacity. The surface aggregate protects the bitumen from the sun and provides a fire-resistant coating.
CAP SHEETS.A cap sheet surface is similar to gravel-surfaced roofings, except that a mineral-surface is used in place of the flood coat and job-applied gravel. Cap-sheet roofing consists of heavy roofing felts (75 to 105 pounds per square) of organic or glass fibers. Mineral-surfaced cap sheets are coated on both sides with asphalt and surfaced on the exposed side with mineral granules, mica, or similar materials. The cap sheets are applied with a 2-inch lap for single-ply construction or a 19-inch lap if two-ply construction is desired. The mineral surfacing is omitted on the portion that is lapped. The cap sheets are laid in hot asphalt along with the base sheet. Cap sheets are used on slopes between 1/2: 12 and 6:12 where weather is moderate.
COLD-PROCESS ROOFING.Cold-applied emulsions, cutback asphalts, or patented products can be applied over the top ply of a hot-mopped roof or as an adhesive between plies. If emulsified asphalt is to be used as art adhesive between plies, special plies (such as glass fiber) must be used that are sufficiently porous to allow vapors to escape. Decorative and reflective coatings with asphalt-emulsion bases have been developed to protect and decorate roofing.
DRAINAGE.When required, positive drainage should be established before the installation of built-up roofing. This can be achieved by the use of lightweight concrete or roofing insulation placed as specified with slopes toward roof drains, gutters, or scuppers.
APPLICATION PROCEDURES .Built-up roofing consists of several layers of tar-rag-felt, asphalt-rag-felt, or asphalt-asbestos-felt set in a hot binder of melted pitch or asphalt.
Each layer of built-up roofing is called a ply. In a five-ply roof, the first two layers are laid without a binder; these are called the dry nailers. Before the nailers are nailed in place, a layer of building paper is tacked down to the roof sheating.
Figure 3-31.-Laying a five-ply built-up roof.
A built-up roof, like a shingled roof, is started at the eaves so the strips will overlap in the direction of the watershed. Figure 3-31 shows how 32-inch building paper is laid over a wood-sheathing roof to get five-ply coverage at all points in the roof. There are basically seven steps to the process.
- Lay the building paper with a 2-inch overlap. Spot-nail it down just enough to keep it from blowing away.
- Cut a 16-inch strip of saturated felt and lay it along the eaves. Nail it down with nails placed 1 inch from the back edge and spaced 12 inches OC.
- Nail a full-width (32-inch) strip over the first strip, using the same nailing schedule.
- Nail the next full-width strip with the outer edge 14 inches from the outer edges of the first two strips to obtain a 2-inch overlap over the edge of the first strip laid. Continue laying full-width strips with the same exposure (14 inches) until the opposite edge of the roof is reached. Finish off with a half-strip along this edge. This completes the two-ply dry nailer.
- Start the three-ply hot with one-third of a strip, covered by two-thirds of a strip, and then by a full strip, as shown. To obtain a 2-inch overlap of the outer edge of the second full strip over the inner edge of the first strip laid, you must position the outer edge of the second full strip 8 2/3 inches from the outer edges of the first three strips. To maintain the same overlap, lay the outer edge of the third full strip 10 1/3 inches from the outer edge of the second full strip. Subsequent strips can be laid with an exposure of 10 inches. Finish off at the opposite edge of the roof with a full strip, two-thirds of a strip, and one-third of a strip to maintain three plies throughout.
- Spread a layer of hot asphalt (the flood coat) over the entire roof.
- Sprinkle a layer of gravel, crushed stone, or slag over the entire roof.
Melt the binder and maintain it at the proper temperature in a pressure fuel kettle. Make sure the kettle is suitably located. Position it broadside to the wind, if possible. The kettle must be set up and kept level. If it is not level, it will heat unevenly, creating a hazard. The first duty of the kettle operator is to inspect the kettle, especially to ensure that it is perfectly dry. Any accumulation of water inside will turn to steam when the kettle gets hot. This can cause the hot binder to bubble over, which creates a serious fire hazard. Detailed procedure for lighting off, operating, servicing, and maintaining the kettle is given in the manufacturers manual. Never operate the kettle unattended, while the trailer is in transit, or in a confined area.
The kettle operator must maintain the binder at a steady temperature, as indicated by the temperature gauge on the kettle. Correct temperature is designated in binder manufacturers specifications. For asphalt, it is about 400°F. The best way to keep an even temperature is to add material at the same rate as melted material is tapped off. Pieces must not be thrown into the melted mass, but placedon the surface, pushed under slowly, and then released. If the material is not being steadily tapped off, it may eventually overheat, even with the burner flame at the lowest possible level. In that case, the burner should be withdrawn from the kettle and placed on the ground to be reinserted when the temperature falls. Prolonged overheating causes flashing and impairs the quality of the binder.
Asphalt or pitch must not be allowed to accumulate on the exterior of the kettle because it creates a fire hazard. If the kettle catches fire, close the lid immediately, shut off the pressure and burner valves, and, if possible, remove the burner from the kettle. Never attempt to extinguish a kettle fire with water. Use sand, dirt, or a chemical fire extinguisher.
A hot rooting crew consists of a mopper and as many felt layers, broomers, nailers, and carriers as the size of the roof requires. The mopper is in charge of the roofing crew. It is the moppers personal responsibility to mop on only binder that is at the proper temperature. Binder that is too hot will burn the felt, and the layer it makes will be too thin. A layer that is too thin will eventually crack and the felt may separate from the binder. Binder that is too cold goes on too thick so more material is used than is required.
The felt layer must get the felt down as soon as possible after the binder has been placed. If the interval between mopping and felt laying is too long, the binder will cool to the point where it will not bond well with the felt. The felt layer should follow the mopper at an interval of not more than 3 feet. The broomer should follow immediately behind the felt layer, brooming out all air bubbles and embedding the felt solidly in the binder.
Buckets of hot binder should never be filled more than three-fourths full, and they should never be carried any faster than a walk. Whenever possible, the mopper should work downwind from the felt layer and broomer to reduce the danger of spattering. The mopper must take every precaution against spattering at all times. The mopper should lift the mop out of the bucket, not drag it across the rim. Dragging the mop over the rim may upset the bucket, and the hot binder may quickly spread to the feet, or worse still to the knees, of nearby members of the roofing crew.