Flat roofs and balconies

7.1.3Flat roof and balcony design

Flat roofs and balconies shall support and transmit loads safely to the structure.

The structural design of flat roofs and balconies should:

  • be produced by an engineer in accordance with Technical Requirement R5, and be in accordance with BS EN 1991-1-1, BS EN 1991-1-3 and BS EN 1991-1-4
  • resist wind uplift by either being of sufficient self-weight or by being anchored to the main structure – where required, holding-down straps should be provided at a maximum spacing of 2m
  • have adequate provision for the additional loads where a flat roof is to act as a roof terrace, roof garden or car parking area
  • have adequate provision for movement in larger roofs, particularly where the span of the roof deck changes, e.g. in L-shaped buildings; joints should be continuous through the vertical upstands, walls and edges of the building
  • include support steelwork and purlins which are square, true and free from twists or sagging.

Where joists and concrete roof elements are used to provide lateral restraint, they should:

  • have a minimum bearing of 90mm, or
  • have restraint straps at 2m centres (maximum) where joists or concrete beams are parallel to walls.