COP v3.0:external-moisture; end-laps

6.4 End Laps 

End laps should be avoided if possible when installing metal cladding. When the sheets are too long to be transported or exceed the longest recommended length (see 6.2.2 Roof Cladding Expansion Provisions) , the transverse or end lap joint can be avoided by using a waterfall step that should be designed into the structure. (See Step Apron Details)

When long lengths are specifically required, secret-fixed roof cladding can be supplied by using an onsite roll-forming machine.

Where end laps are unavoidable a completely sealed joint should be made using a neutral curing silicone rubber sealant at both ends of the lap, with mechanical fastening. (See 6.4A Mechanically Fastened End Lap and 6.4B Sealed End Lap)

The two lengths should be regarded as one length for expansion.

Rivets are used to fix the sheets together and to provide a seal and should not be fastened to the purlin. The sheets are fixed to the purlin by using an oversized hole and a load-spreading washer.

Sealed and fastened sheet-end and flashing laps must be a minimum of 25 mm wide, fastened using rivets with a minimum diameter of 4 mm (5/32) and spaced at 50 mm centres.