CEMP-ET
TI 809-53
01 May 1999
b. General. Crafted metal roof systems require a solid roof deck for support. Both underlayments
and slipsheets are generally used. No. 30 asphalt saturated roofing felt (ASTM D226) is normally used as
sheathing paper. Self-adhering polymer-modified bituminous sheet materials are also used (ASTM
D1970). Rosin sized building paper is used as a separator and slipsheet.
(1) Climate/Weather. These systems are suitable for all climate conditions; however, careful
attention to joints and details are necessary. Eave flashings and sealed underlayments are used where
there is danger of ice damming. Self-adhering modified bituminous sheets can be used but the softening
point of the bitumen must be greater than 93C (200F). Otherwise, the hot metal roof could cause
bitumen drippage. Cold roofs in which the eave beneath the roof membrane is adequately ventilated can
be used where eave icing and snow buildup are of major concern. Designs should include snow guards
and steep slopes (generally 50% [6:12] or greater).
(2) Logistics. Crafted metals can be furnished to the shop or job site in coils or flat sheet stock.
Portable roll formers are sometimes used to form panels.
(3) Familiarity with the System and Site. Crafted metals are a dying art. Master craftsmen are
essential to successful installations. Experience of the installers should be part of the prequalification of
the contractor.
(4) Life Expectancy. Many of these systems have a documented life in excess of 100 years.
Crafted systems use expensive metals as well as considerable labor. These costs are normally justified
by a strong desire for the roof's particular appearance and longevity. The metals are recyclable.
10-2. BUILDING ELEMENTS.
a. Slope. Crafted metals have been used from 2% (1/4 in./ft.) to vertical.
b. Low-Sloped Roofs. At flat or lowest recommended slopes, locked and soldered flat seam
design provides waterproofness. Some architectural systems use waterproof underlayments to lower the
permitted slopes. Provision should be made for any water that reaches the underlayment to weep out on
the down-slope side.
c. Steep Roofs. At slopes well above the minimum recommended slope, watershedding provides
adequate water protection and sealed underlayments are omitted (except where ice damming is likely).
d. Structural Considerations. Some of these systems such as lead are very heavy and the weight
must be considered in the overall design.
e. Expansion and Seismic Joints. Roof panel expansion joints are formed of intermeshed hooked
flanges not less than 25 mm (1 in.) deep. Membrane expansion must be part of the roof design. Refer to
Copper and Common Sense for a discussion. Structural expansion joints generally utilize raised curbs.
For roof runs that exceed 9 m (30 ft.), expansion cleats should be used. Over 14 m (45 ft.), expansion
joints are necessary.
f. Re-entrant Corners. (See SMACNA, Revere Copper and Common Sense, and NRCA Manuals
for details.)
g. Roof Access. Steep roof systems utilizing crafted metals normally will not accommodate
mechanical equipment and associated rooftop traffic. Designs may incorporate a flat roof area hidden
from view by mansard roofs. This hidden roof area may utilize membrane roofing rather than more
expensive metal roofing. This equipment area requires easy access preferably by an internal roof hatch.
10-2
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