Page 197 - Construction Waterproofing Handbook

3.86 CHAPTER THREE
Built-up systems have poor elongation properties, with coal-tar systems being very brittle.
Both asphalt and coal-tar systems do have high tensile strength. As with other sheet sys-
tems, a major disadvantage with built-up roofing is that it allows any water infiltration to
travel transversely until it finds a path to interior areas. This makes leakage causes difficult to
determine, in particular if they are being caused by rooftop equipment or associated transi-
tion detailing. (See Table 3.25.)

TABLE 3.25 Built-Up Roofing Properties
Advantages Disadvantages
Material cost Material quality
High tensile strength Low elongation properties
Multiple layers of protection Difficult construction and safety conditions

Single-ply roofing
Single-ply roofing systems were derived from relatively new technology for use with roof-
ing envelope applications. Used previously for waterproofing, their adaptation to exposed
conditions requires that a membrane be resistant against exposure to weathering such as
ultraviolet rays.
Generic material compositions of single-ply systems are as numerous as waterproofing
systems previously discussed. Their applications range from fully adhered systems to
loose-laid ballasted applications.
Seams continue to be a major disadvantage with any single-ply system. Seaming appli-
cations range from contact adhesives to heat welding. No seaming material or application
system is, however, better than a mechanic’s abilities or training in application procedures.
In addition, termination and transition detailing is extremely difficult using single-ply
systems, especially those involving changes in plane such as roof protrusions. Seam instal-
lations must be carefully monitored during application to ensure installation quality. Most
manufacturers have representatives who inspect installations before architectural or engi-
neering punch-list inspections. (See Table 3.26.)
Single-ply systems should be installed by manufacturer’s approved applicators, and
each project should receive a joint manufacturer and contractor warranty. Guarantees and
warranties are discussed in Chap. 11.

Modified bitumen
Modified bitumen systems are available in a variety of materials and application types.
These include hot-applied liquid membranes and cold-applied systems with protective top
coats. Systems are available with or without fabric or felt reinforcing.

TABLE 3.26 Single-Ply Roofing Properties

Advantages Disadvantages
Manufactured quality control of materials Multiple seams
Weathering durability Termination and transition detailing
Selection of materials available Patching and repairs