Page 199 - Construction Waterproofing Handbook

3.88 CHAPTER THREE
A major advantage of foam roofs is their seamless application, particularly with reme-
dial or reroofing applications. Foam roofs can be installed over many types of existing
failed or leaking roof envelopes, including built-up and single-ply roofing. Minimal prepa-
ration work is required when applying urethane foam roofs in these situations.
The urethane foam portion adds substantial insulation value to a roof, depending on
foam thickness. Foams have an insulation R value of approximately 7 in of foam insulation.
Urethane foam can be installed in various thicknesses and sloped to provide drainage where
1
none currently exists. Typically, foam roofs are installed from 2–6 in thick.
After the urethane foam is installed it must be protected not from water, as it is water-
proof, but from ultraviolet weathering. Foam left exposed is initially waterproof, but ultra-
violet weathering will eventually degrade the foam until leakage occurs.
Thus, coating is applied to provide weathering protection for transitions and termina-
tion detailing. Coatings allow the systems to be self-flashing around roof protrusions and
similar details. Foam roofs are installed in a completely seamless fashion, and their spray
application makes termination and transition detailing relatively simple.
A major disadvantage with foam roofing systems is their reliance on 100 percent job-
site manufacturing. Foam is supplied in two-component mixes that must be carefully
mixed proportionally, heated to proper temperatures, and correctly sprayed in almost per-
fect weather. Any moisture on a roof, even high humidity and condensation, will cause
foam to blister, as urethane foam does not permit vapor transmission. (See Table 3.29.)

TABLE 3.29 Sprayed Urethane Foam Roofing Properties
Advantages Disadvantages
Applications for reroofing Quality-control problems caused by weather conditions
Seamless Completely job-site manufactured system
Termination and transition detailing Safety concerns during application

Protected and inverted membranes
Sheet systems and fluid membranes used in below- and above-grade waterproofing have been
successfully used for protected, sandwiched, and inverted roofing systems. These materials are
identical to those previously discussed under the protected membrane section of this chapter.
Using protected membranes allows the envelope roofing portion to be used for other
purposes including tennis courts and pedestrian areas. A roof area can also be used for
vehicular parking when necessary structural provisions are provided.
Protrusions, particularly HVAC and electrical, are difficult to waterproof since they
penetrate both structural and topping slab portions. If used, all protrusions and similar
detailing should be in place and detailed before membrane installation. After the topping
or protection slab is in place, protection layers should be detailed for additional protection,
including movement allowances. Drainage should be provided at both topping and struc-
tural slab elevations to ensure that water is shed as quickly as possible.
A major disadvantage with these systems is their difficulty in finding and repairing
leakage, since the membrane is inaccessible. These systems require that all applications be
completely flood tested after membrane installation and before topping protection is
installed to prevent unnecessary problems. (See Table 3.30.)