on-
sideration of many factors. Although our expertise is in roof-
ing system design and materials manufacturing, and not in
engineering, architecture, or specialized roof consulting,
GAF does have extensive experience in the practical aspects
of roofing.
Our experience suggests that careful consideration of the
following will provide a fundamentally sound basis for
design and selection of EverGuard
®
single ply roofing
systems.
Building Utilization
Building utilization can have a significant impact on roofing
system selection and design. The most common building uti-
lization considerations are as follows: extremes in internal
temperature/humidity, positive internal pressure, rooftop
traffic/abuse, rooftop-exhausted contaminants, and the use
of the roof as living space. Internal Temperature/Humidity
Extremes in internal temperature/humidity are most often
associated with cold storage/freezer buildings, swimming
pool facilities, drying kilns, food processing plants, per/pulp
mills, and smelting/blast furnace facilities. What makes
these building applications unusual is that the pronounced
difference in vapor pressure between the building interior
and the exterior can cause a pronounced vapor flow through
the roof assembly. This can result in a significant build-up of
condensation within the roof assembly, and severe deteriora-
tion of both the roof assembly itself and the structural deck.
Relevant design considerations include:
Incorporation of vapor retarder at deck level to control
vapor flow into and through roof assembly;
Attention to vapor-tight seal between roof and side
walls/penetrations;
Utilization of closed-cell foam insulation and stainless
steel fasteners to minimize potential for condensation-
related degradation of roof system;
Limitation of penetrations through roof deck;
Avoidance of roof system attachment through vapor
retarder. Positive Internal Pressure
Positive internal pressure is most often associated with man-
ufacturing/clean room facilities, mechanical air-handling
rooms, aircraft hangars, distribution centers with multiple
overhead doors, and high-rise office/residential towers. In all
these instances, positive internal pressures can act on the
underside of the roof system. Conditions where the positive
internal pressure is constant, as in the case of clean room
facilities and high-rise towers, may cause the roof system to
billow up, i.e., mattress effect, and will reduce the overall
uplift resistance of the roofing system. This effect is most
pronounced in mechanically attached systems and can cause
attachment concerns with all three system types. Conditions
where the positive internal pressure is applied suddenly, as in
the case of hangars and distribution centers, may cause fail-
ure of the roofing system due to pressure impact.
Relevant design considerations include:
Use of air-impermeable deck construction such as
poured-in-place concrete or insulating cellular concrete
over steel pan;
Alternatively, installation of an air barrier such as
PVC or PE sheeting at deck level beneath mechanically
attached insulation with attachment sufficient to balance
positive pressure;
Attention to air-tight seal between roof and side
walls/penetrations. Physical Abuse
Roofing installations that can be expected to experience a
high degree of roof traffic due to equipment maintenance,
vandalism or other unauthorized access, frequent hailstorms
or high winds, and prolonged periods of temperature
extremes or rapid fluctuations in temperature, will require a
more durable roofing system. Relevant design considera-
tions include:
Use of thicker membrane or multiple ply membrane,
e.g. Triposite ;
Use of a higher compressive strength insulation
substrate;
Application of a concrete paver or insulated paver
overlay for extreme conditions. Contamination
Many roofing installations are exposed to oil, grease and
chemical contamination in excess of normal air-borne con-
taminants. These conditions are most often associated with
restaurants, food processing plants, chemical and pharma-
ceutical plants, refineries, machining and manufacturing
facilities, and airports. Most roofing materials are degraded
by certain families of contaminants, and will become brittle,
swell and soften, or dissolve, depending on the material for-
mulation and contaminant type. Long-term exposure, i.e.,
28-day immersion testing of roofing material and specific
contaminant, remains the preferred method of determining
material resistance. Even then, unforeseen combinations of
contaminants, environmental exposure effects, and variation in contaminant concentration prevent an absolute prediction in
all but the most common situations. Relevant design/mainte-
nance considerations include:
Use of TPO or PVC membrane in most contaminated roofing
environments;
Isolation of contaminated roof area with expectation of more
frequent roof membrane replacement;
Periodic power washing of roofing membrane with moder-
ate pressure;
Limitation of rooftop spillage/exhaust of contaminating
materials.
Refer to TPO and PVC Chemical Resistance Charts starting
on page 43.
Tear-Off or Recover
The decision to tear-off/replace or to repair/recover an exist-
ing roofing system before installing a new roofing system is
not always clear-cut.
Although not an exhaustive list, the following additional
design elements typically require consideration for any reroof-
ing project:
Replacement of damaged roof decking or structural
components;
Improvement of roof access;
Removal of unused rooftop equipment and associated
equipment mountings;
Remounting of rooftop equipment to allow proper
roofing and flashing technique;
Matching of architectural elements such as special
perimeter metalwork;
Repair of deteriorated parapet and penthouse walls;
Protection of roofing membrane by means of concrete paver
overlay or walkway pad system. Tear-off/Replace
Factors that support the tear-off approach include:
Two or more existing roofs (building code restriction);
Structural weight limitation;
Over 25% existing roof area wet;
Flashing height limitation;
Need to maximize long-term performance.
The basis for any tear-off project is to provide a sound sub-
strate for the installation of a new roofing system and mini-
mize potential damage from tear-off activities. At a minimum,
attention to the following considerations is recommended:
Thoroughly inspect decking, flashing substrates, and wood
nailers before installing new materials;
Plan tear-off strategy so that roof drainage patterns are
never blocked, and so that construction traffic is directed
away from new roof areas;
Protect new roof areas adjacent to tear-off areas from dirt,
debris and damage. Recover
Factors that support the recover approach include:
Need to minimize cost;
Disposal restrictions;
Difficult access to roof.
The basis for any recover project is to eliminate defects in the
existing roof assembly so that their effect on the new roofing
system is minimized. At a minimum, attention to the following
considerations is recommended:
Raise all perimeter flashings, penetrations and equipment
to provide required flashing heights;
Address drainage deficiencies to provide positive
drainage;
Remove and replace all wet roofing materials;
Concentrate on thorough surface preparation.
Roof Decks
Most common structural roof deck types are suitable sub-
strates for the installation of an EverGuard
®
roofing system.
It is the responsibility of the engineer, architect, building
owner or roofing contractor to determine the fitness of a deck
for a specific roofing system installation. Structural Steel
Min. 22 gauge (standard FM-approved steel decking is 22
ga. in thickness).
24-26 gauge decks require EverGuard Contractor Services
approval. Thinner-gauge steel decks usually require addi-
tional mechanical fasteners to achieve comparable roof
attachment performance.
18 ga., 20 ga., and 22 ga. Grade E high-strength steel
decks usually require fewer mechanical fasteners to
achieve comparable roof attachment performance. Structural Concrete
Min. 2500 psi compressive resistance
Min. 2" thickness (precast), min. 4" thickness (poured-
in-place).
Cannot be wet or frozen. If the deck is determined to be
wet, it must be allowed to dry.
For insulated decks, wood nailers of equivalent thickness
56
Roof Design to the roof insulation must be provided at perimeters and
projection openings to act as an insulation stop and to
provide for the nailing of the flanges of metal flashing.
Ridges and other irregularities require grinding to provide
a smooth and even substrate surface.
For non-insulated decks, nailers must be flush with deck
surfaces.
When applying insulation directly to the deck in hot
asphalt, prime with asphalt/concrete primer, ASTM D41,
at a rate of 1 gal/square and allow the primer to dry prior
to the application of the roofing system.
Poured-in-place decks:
must be properly cured prior to application of the roof-
ing system; twenty eight (28) days is normally required
for proper curing. Curing agents must be checked for
compatibility with roofing materials. Prior to the instal-
lation of the roof assemblies, GAF recommends the
evaluation of the surface moisture and decks dryness
through the use of ASTM D-4263 or hot bitumen test.
Pre-cast concrete decks:
are usually manufactured as planks or slabs and con-
structed of steel reinforced Portland cement and solid
aggregate; often they are made with hollow cores to
minimize their weight.
all deformed panels must be replaced.
joints must be