01 May 1999
metal roofs aesthetically pleasing. The silvery metallic color of aluminum and zinc-aluminum alloys may
suffice for industrial roofs.
(4) Waterproof (Hydrostatic) Joints. Hydrostatic joints, which can tolerate brief periods of
submersion, (i.e., hydrostatic pressure) without leaking. The first waterproof (not just watershedding)
joints in metal roofing were soldered flat seams. Thermal movement of the metal works to defeat such
in-plane seams. In the 1960's, the preengineered metal building industry began to use sealants in
structural standing seam panels. Sealant may be factory injected into the female joint component, or field
applied. To be considered for low-slope applications by the Corps of Engineers sealant must be factory
injected. Caution: there are no ASTM tests to verify the performance of waterproof joints in metal roofing.
Even if seams and endlaps are waterproof, the entire system may not be since there are many other
termination and penetration points to consider.
(5) Watershedding (Hydrokinetic) Joints. A hydrokinetic joint relies on slope and gravity, not a
hydrostatic seal, for weather tightness. A watershedding joint would leak if submerged even briefly. To
simulate wind driven rain ASTM E331 tests watershedding joints. The procedure directs a spray at the
joint with reduced air pressure below the assembly. Air pressure is reduced until leaks occur. Some
systems resist leakage much better than others do. Vacuum pressure is not specified by the ASTM test
method. Leakage at 120 Pa (2.5 pounds) differential pressure would be unacceptable while 840 Pa (17.5
pounds) differential pressure would be considered excellent. At this time there is no agreed upon
minimum pressure differential. This test is typically done for the roof panel seams only, not for the other
joints, valleys, eaves, penetrations and ridges present on a metal roof. ASTM E331 also does not
evaluate the effects of slope and underlayment on system performance.
(6) Other Metal Systems. There are metal products produced to look like tile or shingles. They
usually hook together in some fashion and are installed over felts and nailable deck material or furring.
Since they are for steep roofs only, they are discussed in Chapter 8 (Steep Roofing).
(7) Corrugated Metal Roofing. Corrugated metal roofing consists of corrugated structural panels
with exposed fasteners and nested side and end seams. These are structural systems used as water
shedding roofs only. When corrugations are deeper than 25 m (1 in.) spans can exceed 1.5 m (5 ft.).
(8) Copper, Lead-Coated Copper, Terne, Terne-Coated Stainless Steel, and Zinc Metal. These
metals are termed crafted metals and are discussed in Chapter 10. They are also roll formed into
(9) Composite Interlocking Sandwich Panels. Composite interlocking sandwich panels are also
used in the private sector for roofing. The core is usually rigid foam insulation and both skins may be
metal. They are structural systems and often have hydrostatic joints, which allow them to be used on
low-slopes. For Corps of Engineer projects, these panels will only be used on structures that require
b. Climate/Weather. Metal panels must be clean and dry during installation. In pre-engineered
systems, wind can make installation of batt insulation difficult. Metal panel systems have been used in all
climates from tropical to arctic. Climate, slope, roof geometry, construction details, infiltration
characteristics, and underlayment diligence affect roof performance. Metal panels can be shop fabricated
simplifying application in wet or cold weather. Snow will slide easily off of smooth unobstructed metal
surfaces. It may be necessary to install snow guards to eliminate hazards. Roof ventilation is often
needed to prevent ice dams and leaks. Refer to EI01S011 and ANSI/ASCE 7-95 for information on snow
c. Logistics. The length of factory formed panels may be governed by the width of the roof area or
transportation requirements i.e., 12.8 m (42 ft.) for most tractor-trailer beds. Nested panels in bundles