The NZ Metal Roof and Wall Cladding Code of Practice is a comprehensive design & installation guide, and a recognised related document for Acceptable Solution E2/AS1 of the NZ Building Code.
COP v3.0:structure; profile-shape
The corrugated profile has been used in New Zealand for over 150 years and there has been only one significant change during that period. In the 1960s the steel grade used for roof and wall cladding changed from low-strength steel (250MPa or G250) to high-strength steel (550 MPa or G550). The number of corrugations also changed from 8 to 10.5, which enabled the sheets to be laid either side up, as opposed to over-and-under.
The performance of high strength steel corrugated cladding under point and wind loads is much higher than the more ductile grade (G300) still used for machine curving. G300 material of 0.55 mm has the same strength as 0.40 mm high-strength (G550) material; designs using G300 should take the lesser strength into account. G300 material should not be used in lieu of G550 unless there is good reason to do it.
Mixing the two grades of corrugate profile should be avoided when possible. If they are used on the same job, particularly when they are overlapping, the manufacturer should adjust the profile shape to provide an acceptable fit.
Corrugate cladding is formed with a slightly asymmetrical overlap profile to a capillary barrier.
The trapezoidal shape provides greater water carrying capacity and provides greater spanning capabilities than corrugate (sinusoidal) profile. For nomenclature or description of the parts of the sheeting used in this COP, see 2.4 Product Geometry
The maximum available fastener density (fastener per square metre) on deep trapezoidal cladding profiles is usually lower than on corrugate, because of the wider rib spacing and longer spanning capability of stronger profiles.
Trapezoidal profiles are available with different ribs heights (see 3.15A Profile Types).
Trough sections generally have 2 to 3 pans or trays of 180-250 mm width, interspersed with steep ribs. Older profiles may have a single pan. They are secret fixed to minimise fastener penetrations and allow for thermal expansion.
The wide deep pans on trough sections allow for greater water carrying capacity. Traditionally they were used for pitches as low as 1° but due to durability issues (caused by deflection and ponding) the recommended minimum pitch is 3° (see 7.1.1 Minimum Roof Cladding Pitch). Recent innovations in product design have blurred the lines between Trough profile and Standing Seam.
Standing seam roofs are similar to trough sections in that they have a wide pan and a vertical rib, and they are secret-fixed. They are usually wider, having a single tray of 300 mm to 500 mm wide, which gives a unique appearance.
Standing seam roofs are based on traditional manufacturing methods using folding and hand tools, rather than roll forming (see 15.4), but now they are also available roll-formed in most iterations. They are traditionally installed on sarking, but high tensile versions (that do not require continuous support) are available.
Various miniature cladding profiles are manufactured in New Zealand, the most common being known variously under the names of mini-corrugate, sparrow iron, baby iron and mini-iron.
Mini-corrugate is sometimes used for small roof areas, such as spires and awnings. It is most commonly used for wall cladding, parapets and internal linings where studs are normally spaced at 600 mm centres. The accuracy of the framing will determine the quality of finish obtainable.
Mini-corrugate has been produced in New Zealand for many years to the imperial measurement of 1" pitch and 1/4" height, which converts to 25.4 mm x 6.3 mm in metric measurement.
Some miniature trapezoidal profiles are also manufactured specifically for wall cladding.