Find answers to common questions here – these FAQS are designed to provide a better understanding of metal cladding building systems and their various applications.

If you cannot find the answer to your question here, please contact MCRMA on 01633 895633 or via the technical hotline.

Air-tightness requirements mean that the effective side and end lap sealing of lining sheets in built-up cladding systems is key. The sealing of side laps on lining sheets also contributes towards the effective sealing of the building against the transfer of vapour from the inside of the building into the cavity.
Side lap sealing: During the site assembly of built-up cladding systems the side laps of the joints between adjacent lining sheets must be sealed adequately using 50mm x 1mm tape. The sealing strip must lap either side of the side joint and must be in full and bonded contact along the length of the sheet. Cold or damp site conditions can affect the adhesive properties of the tape; therefore ensure that the tape is “brushed down” onto the joint before the insulation is laid.
End lap sealing: The end lap of lining sheets must be fully sealed to provide adequate air and vapour sealing. Butyl strip should be positioned within the end lap in a continuous unbroken length and it should form around the shape of the profile without stretching. Particular care should be taken at corners and junctions to ensure continuity of the seal. To complete the end lap joint a series of fasteners should be inserted through the lap into the underlying purlin to pull the joint together and provide fixture for the lining panels.

Built up system end lap detail (metal over GRP rooflight), three runs of butyl sealant

The position and size of butyl mastic seal in the overlap joints of outer sheets can have a significant effect on the overall performance and weather tightness of profiled roofing and cladding systems. The sealing strip is introduced into the lap to prevent the ingress of dirt and water from the weather side and to prevent the potential risk of condensate from entering the top of the lap from the inside.

The sealing strip or bead must be in full contact with both surfaces of the joint; it must be flexible enough to deform around the shape of the profile, resilient enough not to compress excessively under load and yet be flexible enough to withstand movement within the joint. The expansion characteristics of the sealant must be able to accommodate the full movement of the joint and therefore must be specified accordingly. It must also last the life of the building without degrading or cracking.

Please note:

Any uncertainty about the use or application of a product or system should be referred back to the manufacturer for detailed written advice. Manufacturers are best placed to offer advice about their particular products and any variation from their published data during the design or construction process could result in the component or system failing prematurely or not complying with the guarantee or warranty conditions. Additional project specific advice for demanding or complex constructions may also be obtained from one of the independent consultants featured on the MCRMA web site.