Structural roof decking with MCRMA – all the info

  • 1 Apr 2021

Structural roof decking offers the benefits of long span construction, enabling the design of lighter and more economic structures, explain the MCRMA.

Structural decks feature within many high performance roof installations, typically supporting secret-fix/standing seam outer skin roof products.

Roof deck profiles

By spanning a decking profile from rafter to rafter, there is no need for purlins in a portal frame design.

A structural deck will perform the function of transferring dynamic and dead loads of the roof covering to the frame. It will also provide the necessary lateral restraint to the main structural frame.

It is also possible to design a ‘diaphragm’ roof (often referred to as a ‘stressed skin’ design).

Structural decks offer the benefits of long span construction, enabling the design of lighter and economic structures. 

Whilst meeting the stringent performance requirements that legislation demands, flexibility of these products allows the designer more freedom. This enables clean internal lines and a multitude of options such as convex and concave and even tapered curve elevations.

Profiled roof decking is the self-supporting structural element used with:

 – Single ply membrane
 – Standing seam systems
 – Green roofs
 – Slates and tiles
 – Three ply felt
 – Asphalt


  • Available in a wide range of profile depths to accommodate structural needs and long span applications
  • It’s possible to perforate desks to prove an inner layer, backed by a range of acoustic membranes and insulation types
  • Profiles available in both steel and aluminium and in a range of colours to suit internal aesthetics

Roof deck and single ply systems

Roof deck and single ply systems provide a long spanning alternative to built-up cladding on cold formed purlins. These are especially popular on ‘flat’ or very low pitch roofs on which a waterproof membrane is required.

The roof construction comprises a trapezoidal profiled metal deck of sufficient depth and gauge to span directly between the rafters, roof beams or trusses.

A common metal deck typically has a profile height of 100mm although deck profiles are available from shallow profiles through to profiles which are in excess of 200mm deep and a range of material thickness to suit the application.

The deck supports a layer of rigid insulation, on top of which the waterproof membrane is. The use of a high-density rigid membrane permits the loads from foot traffic and snow to be carried through the insulation layer to the structural deck, eliminating the need for a metal top sheet or spacer system.

The deck is capable of restraining the top of the beam or truss, making it ideal for building designs that have simply supported roof structures.

However, structural decks are not suitable for plastically designed portal frames, due to the need to restrain the inner flange of the rafter in the hogging region.

Single ply roofing design guide

The Single Ply Roofing Association’s comprehensive design guide to single ply roofing design, Single Ply Roofing Design Guide 2020 Edition (S1/2020), is available for download via the MCRMA’s website.


Metal Cladding and Roofing Manufacturers Association (MCRMA),
106 Ruskin Avenue,
NP10 0BD.

Tel: 01633 895633


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