Built-Up Roofing - Page 5

Built-Up Roofing Specifications

Coatings and surfacings will require periodic recoating. The frequency of re-coating will depend on the quantity and quality of application and numerous climatic and environmental factors.

6.10 Gravel and Slag Surfacings

6.10.1 Gravel or slag must be dry before using. Wet gravel or slag will cause foaming of the asphalt and prevent proper adhesion of the surfacing. In cold weather, if difficulty is experienced in obtaining proper embedment in the asphalt, the gravel or slag should be heated prior to application.

6.10.2 JM will approve the use of clean slag or gravel meeting ASTM D 1863, which applies to aggregates specified both for use in road construction and bituminous roofing. Aggregates meeting ASTM D 1863 are generally available commercially throughout the country.

6.10.3 Other surfacing material used in place of gravel or slag should be fairly cubical in shape, non-water-absorbent, hard and opaque, and of such size and nature as to result in firm embedment in the asphalt.

6.10.4 Do not use transparent or translucent stones, such as dolomite or crushed masonry.

6.10.5 Flood the surface with the appropriate hot asphalt for the roof slope, at an approximate rate of 60 lbs. per square (2.9 kg/m²). While the asphalt is still hot, embed the surfacing.

6.10.6 Gravel should be spread at the rate of 400 lbs. per square (19.5 kg/m²). Because of its lower weight in relation to volume, slag should be applied at the rate of 300 lbs. per square (14.6 kg/m²). In any case, sufficient amounts of gravel or slag should be applied to result in full and complete coverage of the roof surface with approximately 50% of the aggregate solidly adhered in the asphalt.

6.11 BUR Steep Slope Requirements

6.11.1 Built-up roofing membranes can be applied on inclines up to 6" per foot (500 mm/m) when proper precautions are taken. On non-nailable decks wood nailers must be used. Nailers act as insulation stops for the roof insulation and as a facility to nail the fiber glass built-up roofing felts.

6.11.2 Spacing of Nailers
On decks where the incline is such that nailing of roofing felts is required (2" [51 mm] and over for smooth surfaced roofs and 1" [25 mm] and over for gravel and mineral cap sheet surfaced roofs), wood nailing strips, 3 ½ " [89 mm] minimum actual width) should be provided at the ridge and at the following approximate, intermediate points:

Nailer Spacing and Type of Asphalt/Cap Sheet Roofs:

Nailer Spacing and Type of Asphalt/Smooth Surfaced Roofs:

Nailer Spacing and Type of Asphalt/Gravel-Surfaced Roofs:

† Consult a JM Technical Service Specialist regarding projects in hot
   climates as Type II Asphalt may not be permitted in some areas.

6.11.3 Nailing strips should be the same thickness as the insulation, and at least 3 ½ " (89 mm) wide. They should be securely attached to the deck with mechanical fasteners to resist a pullout force of 200 pounds (890 N). Nailers should run at right angles to the incline of the roof slope.

6.11.4 Nailable and Lightweight Concrete Decks
On decks where the incline is over 1" (25 mm) for gravel surfaced or cap sheet systems and 2" (51 mm) for smooth surfaced systems, the felts must be installed parallel to the incline. Ply felts and cap sheets are to be backnailed ¾ " (19 mm) from the leading edge at intervals equivalent to the nailer spacing shown in the table above.

6.11.5 Felt Application
Felts used in smooth surfaced roofs must be installed parallel to the roof incline, on slopes greater than 2" per foot (166.6 mm/m). This requirement applies to gravel and mineral surfaced roofs at slopes greater than 1" per foot (83.3 mm/m). Nails must have a 1" (25 mm) minimum diameter cap. Where capped nails are not used, fasteners must be driven through caps having a minimum diameter of 1" (25 mm).