Flat roofs and balconies

7.1.6Concrete decks

Concrete flat roofs and balconies shall form a satisfactory substrate for the waterproofing system.

Concrete flat roofs should be constructed to ensure they achieve the required design, strength and durability, and be in accordance with BS EN 1992-1-1 and Chapter 3.1 ‘Concrete and its reinforcement’.

In-situ reinforced concrete decks should:

  • be formed using a mix which has low shrinkage characteristics
  • have accurately constructed and suitably supported formwork
  • be protected until adequately cured and dried (permanent waterproofing should not be installed until the deck has fully dried).

Precast concrete decks should:

  • be installed on an even and true supporting structure
  • have a minimum 90mm bearing (unless the design specifies a smaller dimension)
  • have allowance for continuity or anti-crack reinforcement
  • have allowance for movement approximately every 15m and at abutments
  • be installed to provide an even surface
  • be grouted, as specified in the design.