8.12 - Airtightness
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!
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