Forming service holes in composite slabs


Openings and service holes are regularly required through composite slabs to allow services to pass from floor to floor. A summary of industry best practise and guidance for SMD floor deck products can be seen below.


Openings can be grouped by deck profile and size:

When forming voids, the following should be noted;

  • Voids should be boxed out and the deck cut after the concrete has cured
  • Non-percussive cutting methods should be used to minimise disturbance of the composite bond between deck and concrete
  • Voids should be isolated and not closely grouped
  • Minimum spacing should be the greater of 300mm or 1.5x diameter, from edge to edge
  • No more than ¼ of total span length should be removed
  • Responsibility of design for additional reinforcement, trimming steels and structural verification lies with the project engineer
  • Concentrated loads should not be applied near void locations

VoidSafe, an alternative void solution

VoidSafe™ Protection System can significantly improve site logistics and access throughout the floor area.

For more information on this topic, see our TGN Section 5.6 specifically relating to Forming Service Holes.

TGN Online

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By Thomas Rigden GMICE

SMD Technical Design Engineer

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