Flat roofs, terraces and balconies

7.1.8Profiled self-supporting metal decks

Profiled self-supporting metal decks shall form a satisfactory substrate for the flat roof build-up. Issues to be taken into account include:

  1. Structural performance
  2. Material and profile
  3. Roof build-up.

Structural performance

Profiled self-supporting metal flat roofs should:

  • be constructed to ensure they achieve the required strength and durability, and be checked for conformity with the design upon delivery
  • comply with the manufacturer’s load and span tables and the relevant applied safety factor
  • conform to BS EN 1090-4 (steel) and BS EN 1090- 5 (aluminium) and resist loads in accordance with BS EN 1991-1-1,3 & 4 and be fixed in accordance with the manufacturer’s instructions
  • be side lap stitched to ensure it performs as a continuous plane layer (unless the manufacturer recommends otherwise)
  • be adequately protected from construction loads
  • be suitably stored to prevent damage

Material and profile

Profiled self-supporting metal flat roof sheeting should:

  • be galvanised steel to BS EN 10346 (typical gauge range 0.7-1.2mm) or aluminium to BS EN 485-2 (minimum gauge 0.9mm) and used in accordance with BS EN 1993-1-3 and BS EN 1999-1-4 respectively
  • have a crown which is a minimum of 45% of the profile width (for bonded systems) (not including the crown stiffener grooves)
  • have a crown which is minimum of 40% of the profile width (for mechanically fixed systems)
  • be of suitable quality and finish before the waterproofing layer and insulation system is installed.
  • be fixed using suitable fixings which avoid bimetallic corrosion in accordance with the manufacturer’s recommendations.

Roof build-up

The roof build-up should:

  • be a ‘warm’ or ‘inverted warm’ roof design
  • have drainage falls formed by installing the profiled metal sheeting at a slope or by use of tapered insulation.
  • use insulation board with a compressive strength capable of spanning across the troughs of the profiled sheeting without crushing or be laid on a support board fixed across the profiles
  • use a reinforced air and vapour control layer, or AVCL recommended by waterproofing manufacturer, in warm roof build-ups where unsupported across the troughs.
  • incorporate a support board fixed profiles in inverted warm designs to fully support the waterproofing layer.

Warm roof construction – with metal deck

Inverted warm roof construction