Openings in Structural Roof Decks

Rules and design considerations

Openings are often required to be formed through structural roof decks.  Here are some basic rules and information on the size, detailing considerations and design implications.


Openings in Structural Roof Decks can be grouped into three categories;

Small Openings (Trough Width)

  • Max Opening Size (DMax) < Trough Width.
  • Minimum spacing of openings is 20 x DMax.
  • No material can be removed from the profile web.

Medium Openings (Pitch Width)

  • Openings up to one pitch width are allowed.
  • A 2.0mm thick square stiffener plate extending 1 pitch width in all directions from the perimeter of the opening is required.
  • Maximum of one opening in the direction of deck span, per span.
  • The stiffener plate must be installed before cutting of the roof sheet.

Large Openings (Greater than Pitch Width)

  • Additional structural supports are required for all Large Openings.
  • The deck profile should not be designed to carry any loads from within the opening. E.g.- Roof lights.

These are guidelines only and particular requirements should be checked by the Project Engineer. SMD’s responsibility excludes the design and installation of any additional structural supports, the static verification of roof decks with openings and the subsequent cutting of the deck sheet. Should point loads be required, additional trimming steel work will be required. When forming openings, consideration needs be given to Health & Safety especially the increased risk of falls from height.


You can now create calculations with SMD Roof Deck profiles using the latest version of SMD Elements®

For more information on this topic, see TGN Online Section 8 (Table 8.18a) of trough and pitch width’s for all SMD Roof Decks.

TGN Online

For In-depth Technical Guidance Notes on a range of topics, refer to TGN Online

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By Thomas Rigden GMICE

SMD Technical Design Engineer

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