ESSENTIALS FOR A SUCCESSFUL FLAT ROOF

Like any part of a building’s exterior, flat roofs should be constructed to withstand natural and human forces with the minimum of attention. The following general guidance can be confirmed by the specific membrane manufacturer.

We have prepared this guide for householder’s and homeowners with minimal roofing knowledge. By providing information on the design, materials, construction and maintenance of successful flat roofs; we hope it will assist you to a satisfactory completion with your roofing project.

Like any part of a building’s exterior, flat roofs should be constructed to withstand natural and human forces with the minimum of attention. The following general guidance can be confirmed by the specific membrane manufacturer.

Protection from Rain and Snow

  • The finished roof should have a slope of at least 1 in 80. To achieve this, a design fall of 1 in 40 or 1 in 60 is advised.
  • It is best to drain the roof to one or two edges.
  • Conventional gutters are better than internal outlets.
  • Internal outlets should be adequately sized to deal with storm conditions and be fitted with leaf and gravel guards.
  • The waterproofing should extend up adjacent walls at least 150mm (6in) from the roof surface in all situations.
  • The top edge of the waterproofing system should be protected by a cover flashing appropriate to the membrane.

Protection from Sun and Frost

  • It pays to insulate: heating bills are lower throughout the year and rooms are cooler in the summer.
  • Insulation of new flat roofs must satisfy Part L of the Building Regulations. Since April 2006, this also applies to refurbishment of flat roofs.
  • Bitumen membranes should be protected from the sun.

Protection from Condensation

  • It is essential that cold roofs include adequate through-ventilation of all joist voids etc.
  • Warm roofs always require a robust vapour control layer (VCL), bonded directly to the deck.

Protection from the Wind

  • All roofs, including insulation and membrane, should be constructed to resist wind forces.
  • An experienced contractor will be able to advise. Seek his advice if your roof is particularly exposed.

Protection from People

  • Materials should be selected to suit roof usage. If regular foot traffic is expected a surface protection must be provided.
  • If the use is changed, e.g. to a roof terrace, the structure may have to be strengthened.

Protection from Fire

  • Consult your local authority if you are planning a new flat roof.
  • Most flat roof systems will meet the Regulations, but check with your contractor.