Sealant or sealant tape, such as butyl, may need to be used in the seams.

NRCA also recommends a minimum underlayment of an ASTM D4869 Type III or Type IV (No. 30) asphalt-saturated felt underlayment and separate slip sheet, such as rosin-sized sheathing paper or underlayment with slip-sheet capabilities, beneath architectural metal roof panels.

Also, for some types of metal, it may be necessary to ventilate the architectural metal panel’s underside.

Exceptions

Because flat-seam metal panel roof systems with nonsoldered seams are intended to shed water, they are found in architectural metal applications with slopes of 4:12 or greater and not recommended for applications with lower slopes.

Likewise, though snap-together seaming systems are considered standing seams, some have relatively poor water resistance, restricting their use to steep-slope, architectural applications.

When designing a metal panel roof system, designers should consider fastening requirements. The fastening schedule and substrates need to provide adequate anchorage to resist design wind-uplift pressures.

It is the designer’s responsibility to determine the acceptability of a fastener type for a roof system and roof substrate. Pull-out resistance and the ability of a fastener to hold material in place should be primary considerations. These characteristics are a function of the substrate type and strength and the fastener’s size, shank, point or tip type, and thread design. The corrosion resistance of a fastener also should be considered along with its desired service life, which should be equivalent to that of the roof system. A fastener should be compatible with the material being secured and the substrate into which it is embedded.

The 2021 IBC explains some of the restrictions in metal type for fasteners: “1507.4.4 Attachment. Metal roof panels shall be secured to the supports in accordance with the approved manufacturer’s fasteners. In the absence of manufacturer recommendations, the following fasteners shall be used:

1.Galvanized fasteners shall be used for steel roofs.

2.Copper, brass, bronze, copper alloy or 300 series stainless-steel fasteners shall be used for copper roofs.

3.Stainless-steel fasteners are acceptable for all types of metal roofs.

4.Aluminum fasteners are acceptable for aluminum roofs attached to aluminum supports.”

Know the options

There is a variety of metal panel roof systems on the market fabricated in a variety of ways. As with traditional steep- and low-slope membrane roof systems, no one system is best for all applications. When choosing a metal roof system, a roof system designer must consider the following:

- Project requirements

- Roof slope

- Whether continuous or closely spaced decking will be used to support the panels or panels will be required to span between structural members

- The system’s exposure to climatic and environmental conditions

- Moisture control and ventilation for interior conditions

-  Aesthetic characteristics

- Desired life expectancy and potential maintenance

- Appropriate details for the building and selected system

- Applicable code requirements

Original Source Information

https://www.professionalroofing.net/Articles/Discussing-the-differences--10-01-2021/4956