Flat roofs, terraces and balconies

7.1.9Profiled self-supporting metal roofing

Profiled self-supporting metal roofing shall be of adequate strength and durability, and resist the passage of water to the inside of the building, and provide an adequate level of thermal and sound insulation

Profiled self-supporting metal sheet roofs should be designed and constructed in accordance with:

  • BS 5427 CoP for the use of profiled sheet for roof and wall cladding
  • BS EN 14782 Self-supporting metal sheet for roofing, external cladding and internal lining. Product specification and requirements
  • BS EN 14509 Self-supporting double skin metal faced insulating panels – Factory made products – Specification
  • BS EN 508- parts 1,2 and 3 Roof and cladding products from metal sheet. Specification for self-supporting products of steel, aluminium or stainless steel.
  • BS EN 506 for self-supporting copper and zinc
  • BS EN 1991-1-1,3 & 4 for structural loads and be fixed in accordance with the manufacturer’s instructions

Profile sheet roofing can be:

  • Site assembly - including self-supporting metal liner, outer metal profile, held apart by site installed structural support system, with insulation between liner and profile layer.
  • Factory insulated panels (i.e. sandwich or composite panels) - metal inner and outer skins adhesively or cohesively factory bonded to a thermal insulation to form a composite self-supporting assembly.

An air and vapour control layer must be provided on the warm side of the insulation.

Notes

Subject to the profile manufacturer’s recommendations the AVCL can be formed by sealing the side and end laps of the metal liner or by the provision of a separate AVCL membrane directly above the inner liner. The AVCL must be fully sealed around all penetrations and at the roof perimeter and have a vapour resistance of at least 500 MNs/g. Note: if high density polythene is used it must be reinforced 1000 gauge or more and of virgin material.

Insulation should contact both the inner and outer metal layers. Any voids formed by the profile of the outer sheet metal roof covering should be ventilated. Ventilation can be achieved by leaving open the profile at both ends of the sheeting above the insulation. If profile fillers are fitted, they should leave a free area of not less than 5% of the cross-sectional area of the void. Where the insulation is likely to be affected by local condensation, a breather membrane should be provided on top of the insulation to discharge condensate externally in accordance with the profile manufacturer’s recommendations.

The profiled panels should be fixed using suitable fixings which avoid bimetallic corrosion in accordance with the manufacturer’s recommendations.

Twin skin build-up

Standing seam roof (secret fixings)

Example of edge seal with composite roof panels

The panel side laps, and end laps should be sealed to provide an air barrier as part of the overall air leakage and vapour control requirement of the building, in accordance with the panel manufacturer’s instructions.