overlaps a shingle next to it in the same course. The areathat one shingle overlaps a shingle two courses below itis known as head lap. Head lap is measured from thebottom edge of an overlapping shingle to the nearest topedge of an overlapped shingle. “Exposure” is the areathat is exposed (not overlapped) in a shingle. For the bestprotection against leakage, shingles (or shakes) shouldbe applied only on roofs with a unit rise of 4 inches ormore. A lesser slope creates slower water runoff, whichincreases the possibility of leakage as a result ofwindblown rain or snow being driven underneath thebutt ends of the shingles.Slope“Slope” and “pitch” are often incorrectly usedsynonymously when referring to the incline of a slopedroof. View B of figure 3-13 shows some common roofslopes with their corresponding roof pitches.“Slope” refers to the incline of a roof as a ratio ofvertical rise to horizontal run. It is expressed sometimesas a fraction but typically as X-in-12; for example, a4-in-12 slope for a roof that rises at the rate of 4 inchesfor each foot (12 inches) of run. The triangular symbolabove the roof in figure 3-13, view B, conveys thisinformation.Pitch“Pitch” is the incline of a roof as a ratio of thevertical rise to twice the horizontal run. It is expressedas a fraction. For example, if the rise of a roof is 4 feetand the run 12 feet, the roof is designated as having apitch of 1/6 (4/24= 1/6).MATERIALSIn completing roofing projects, you will be workingwith a number of different materials. In the followingsection, we will discuss the most common types ofunderlayments, flashing, roofing cements, and exteriormaterials you will encounter. We will also talk aboutbuilt-up roofing.Materials used for pitched roofs include shingles ofasphalt, fiberglass, and wood. Shingles add color,texture, and pattern to the roof surface. To shed water,all shingles are applied to roof surfaces in someoverlapping fashion. They are suitable for any roof withenough slope to ensure good drainage. Tile and date arealso popular. Sheet materials, such as roll roofing,galvanized steel, aluminum, copper, and tin, aresometimes used. For flat or low-pitched roofs,composition or built-up roofing with a gravel topping orcap sheet are frequent combinations. Built-up roofingconsists of a number of layers of asphalt-saturated feltmopped down with hot asphalt or tar. Metal roofs aresometimes used on flat decks of dormers, porches, orentryways.The choice of materials and the method ofapplication are influenced by cost, roof slope, expectedservice life of the roofing, wind resistance, fireresistance, and local climate. Because of the largeamount of exposed surface of pitched roofs, appearanceis also important.UnderlaymentsThere are basically four types of underlayments youwill be working with as a Builder: asphalt felt, organic,glass fiber, and tarred.Once the roof sheathing is in place, it is covered withan asphalt felt underpayment commonly called roofingfelt. Roofing felt is asphalt-saturated and serves threebasic purposes. First, it keeps the roof sheathing dryuntil the shingles can be applied. Second, after theshingles have been laid, it acts as a secondary barrieragainst wind-driven rain and snow. Finally, it alsoprotects the shingles from any resinous materials, whichcould be released from the sheathing.Roofing felt is designated by the weight per square.As we mentioned earlier, a square is equal to 100 squarefeet and is the common unit to describe the amount ofroofing material. Roofing felt is commonly available inrolls of 15 and 30 pounds per square. The rolls areusually 36 inches wide. A roll of 15-pound felt is 144feet 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-poundfelt will cover 4 squares; a roll of 30-pound felt willcover 2 squares.Underpayment should be a material with low vaporresistance, such as asphalt-saturated felt. Do not usematerials, such as coated felts or laminated waterproofpapers, which act as a vapor barrier. These allowmoisture or frost to accumulate between theunderlayment and the roof sheathing. Underlaymentrequirements for different kinds of shingles and variousroof slopes are shown in table 3-5.Apply the underpayment as soon as the roofsheathing has been completed. For single underpayment,start at the cave line with the 15-pound felt. Roll across3-12
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