CEMP-ET
TI 809-53
01 May 1999
may be hoisted to the roof framing, provided the bundles are placed directly over the structural members
and the weight is distributed to avoid overload.
d. Familiarity with the System and Site. Metal panel roofing systems are proprietary and should be
installed by a manufacturer-approved, experienced installer.
e. Life Expectancy and Cost. Hot dip coatings of aluminum or zinc-aluminum can give 20 years of
service in all but the most corrosive atmospheres. Colored coatings of poly-vinylidene difluoride (Hylar
5000 and Kynar 500) and all-aluminum panels are also very durable. Metal roof systems generally
have a much higher first cost than other roofing types discussed in this EI; but on a life cycle basis this
may be justified because of greater durability and lower maintenance costs. Zinc-coated steel
(galvanized) is less expensive but far less durable for unpainted (bare) applications. As a corrosion
resistant base for color coatings, galvanized steel is still widely used in prepainted applications. Structural
and nonstructural metal roof systems may have approximately the same installed cost. Steel and
aluminum roof systems are recyclable. Glass fiber batts and plastic foam may be reusable or recyclable
since the material is essentially uncontaminated by bitumen or other foreign material. Composite panels
are difficult to recycle.
f. Occupancy Considerations. For high humidity occupancy in temperate or cold climates,
conventional structural panel systems with faced batt insulation will not be adequate as it is difficult to
seal the vapor retarder so it resists air exfiltration. A preferred metal roofing system would include a
vapor retarder and rigid board insulation above the structural deck followed by a ventilated airway and the
roof panel. An alternative would be to use an interlocking insulated panel system. In hot, humid climates
condensation has been observed on the backside of metal panel systems when rain cools the panel
quickly. Installation of a sealed plastic sheet (e.g., 4 mil polyethylene) directly underneath the metal
panel will protect the back of the panel against condensation-caused corrosion.
9-2. BUILDING ELEMENTS.
a. Slope. Minimum slope varies with the type of panel (architectural or structural), the type of joint
(watershedding or waterproof), and the amount of rain or snow expected at the site. Table 9-1 presents
design requirements.
Table 9-1. Minimum Slope for Metal Roofing
%
in./ft.
Metal panel roofing with watershedding (not waterproof joints)
Architectural (nonstructural) panels
33
4
Structural panels wider than 305 mm (12 in.)
33
4
Architectural panels with seams at least 38 mm (1-1/2 in.), but less than
25
3
51 mm (2-in.) high, with underlayment
Structural panels no wider than 305 mm (12 in.), with seams at least
25
3
38 mm (1-1/2 in.), but less than 51 mm (2 in) high, with underlayment
Architectural panels with seams at least 51 mm (2 in.) high, with underlayment
and structural panels no wider than 305 mm (12 in.,) with seams at least
51 mm (2 in.) high.
Where the ground snow load is more than 98 kg/m2 (20 psf)
25
3
Where the ground snow load is 98 kg/m2 (20 psf) or less
17
2
Metal panel roofing with factory installed seam sealant designed and tested
to be waterproof (i.e., to withstand hydrostatic pressure) and with field joints
designed and sealed to the same high level of watertightness
Where the ground snow load is more than 98 kg/m2 (20 psf)
8
1
Where the ground snow load is 98 kg/m2 (20 psf) or less
4
1/2
9-3
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