8.12 - Airtightness

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As recommended by MCRMA, to minimise air leakage through twin skin metal roofing, the liner side of the construction must be sealed as effectively as possible. To provide an effective seal, this will typically involve sealing at the following locations:

End Laps Typically using butyl strip with 8/10mm bead as follows:

Up to SR60+ 8mm bead

SR100 and above 10mm bead

Side laps and Perimeter Side Joints

Typically with 1mm x 50mm wide butyl tape

Fasteners

Use standard washers

Perimeter or butt ends in sheets

Profiled filler blocks, contact SMD Technical Team for info.

Around Penetrations, such as pipes

Sealant tape and/or flexible flashing

With a good standard of workmanship, taking care and attention to detail, a twin skin metal roof structure meeting the air tightness requirements of Approved Document L can be easily achieved.

It should be noted that the roof cladding is only one part of the envelope that contributes to air leakage. In certain situations, junctions at windows, doors, roof lights, smoke vents etc. may be more critical and hence, the attention to detail must apply to all elements of the building envelope.

Important – Any filler or sealant is only as good as the workmanship installing the detail!

Other items within 8.0 - Design - Roof deck:-

8.0 - Design - Roof deck

8.1 - Quality

8.2 - Spans

8.3 - Loads

8.4 - Standard end laps

8.5 - Extended end laps

8.6 - Raking supports and cutting

8.7 - Cantilevers

8.8 - Sheet lengths

8.9 - Fire rating