End laps should be avoided if possible when installing metal roof cladding as an incorrectly sealed end lap may entrap water and cause corrosion. When the sheets are too long to be transported or exceed the longest recommended length (see 7.3.2 Roof Cladding Expansion Provisions), the transverse or end lap joint can be avoided by using a waterfall step. (See 8.5.5.3A Step Apron Details)
When long lengths outside the capacity of available transport are required, secret-fixed roof cladding can be supplied by using an onsite roll-forming machine.
Where end laps are unavoidable, a sealed joint should be made using sealant at both ends of the lap. The upper seal is critical as condensation entering the upper side of the lap from underneath can cause rapid corrosion. (See 14.12.1 Sealing End Laps.) Rivets are used to fix the sheets together and should not be fastened to the purlin. The sheets are fixed to the purlin using screw fixings.
The two lengths should be regarded as one length for expansion provisions.
As with roofing, wall cladding sheets should, wherever possible, be laid in a single continuous length. Where this is not feasible due to excessive length or other constraints, there are options for lapping.
When the internal environment is dry and the wall is unlined, sheets can be simply end-lapped by approximately 150 mm. In dwellings, lined buildings, and buildings with moist internal environments, the laps should be sealed at both ends as per roof laps. The downside of end lapping is that there are four layers of material at the side lap/end lap junction. This often leads to an untidy looking join.
