Ian Burns of Corus Colourcoat gives his five top tips for the trouble-free installation of pre-coated metal roof cladding
Sealants are the practical means of achieving a weathertight metal clad roof, particularly with the trend towards lower pitches. The end laps of roofing sheets should be sealed with two rows of sealant, one on each side of the line of fasteners.
If using standing seam or concealed fix profiles, consult the maker about whether sealants should be used and, if so, how and where. When applying sealant to the leading edge of sheet overlaps, take care that the sealant does not exude under compression and thereby create a dam at the edge of the lap, which could trap water and dirt. It is very important to remove all drilling swarf and other debris during installation. A common cause of rust staining and localised corrosion attack is swarf and installation debris such as broken-off stems from pop rivets, which, if left on roof sheeting, will quickly corrode and cause unsightly surface staining. All such debris should be swept or removed from the roof immediately. Pre-coated metal products are made to produce consistent colours, but slight variations can occur between coils coated at different times. If tonal consistency is critical, all sheeting for a single elevation should come from the same production batch. This applies to all cladding, but variation is more noticeable in light colours. Indeed such variation is characteristic of all coloured products.Metallic effects can often have a directional quality as a result of the coating process, which causes all the metallic flakes to lie in a similar direction. This should be taken into account during construction.Some methods of cutting sheets can cause damage, which will affect the appearance and the performance of the building. Cutting with an abrasive disc is not recommended as it is difficult to get a clean line with this method and there is a risk of damaging the coating.
Cutting with a hacksaw leaves a rough edge. If cutting by saw is essential, use a jigsaw or circular saw with the appropriate metal cladding blade, taking care to ensure a clean cut. Control the cutting speed and ensure adequate cooling to prevent damage from overheating. The recommended method is to use a sheet nibbler, which gives a very clean edge and does not damage the sheet. This also makes it easy to cut complex holes through the sheet.