Waterproofing and sealing
of flat roofs

Roofing universes

Flat roofs, whether on collective or individual buildings, have become an integral part of the built environment. Constructing and maintaining this type of roof requires know-how and specific equipment. Dimos provides the right tools for new roofing markets and techniques, and helps you to ensure safety.

A fundamental
architectural trend

Flat roofs have long been standard on large residential buildings, but recently, this trend has been spreading to single-family houses, which can be seen popping up everywhere. For new or renovated buildings, flat roofs have become a symbol of modernity.

Their success can be attributed to the multitude of advantages they offer in terms of configuration. They provide more space: large roof-top surfaces can increase the amount of daylight inside buildings, and can also be converted into roof terraces or green roofs. In addition, the emergence of new materials and techniques has reduced costs, making this type of roof more affordable and within more people’s reach.

In France, impervious surfaces such as roof-tops account for approximately 22 million m2 per year. (source CSFE).

Waterproofing & sealing

While being important for all roof types, waterproofing is particularly essential for flat roofs (0 to 5°/1.05:12) or low sloping roofs (<15°/3.22:12): this type of roof must be completely impervious to water to prevent water infiltration, which can profoundly damage the building envelope.

It is therefore essential to observe waterproofing standards for terrace roofs specified by the building code.

The rules of practice for waterproofing flat roofs depend on two main factors: accessibility and protection. Consequently, these rules are based on watertight integrity, resistance to cracking, elasticity, resistance and compatibility with other materials.

Specific potential problem areas (called “vigilance points”) are outlets (e.g. ventilation and chimney outlets). Guttering should slope towards the downspouts to drain rainwater.

Waterproofing & sealing
a roof

A flat roof’s structure consists of 4 elements:

  • the supporting structure, which is usually made of reinforced concrete, steel or wood
  • a vapour barrier to prevent condensation and moisture
  • a thermal insulator, which varies depending on how accessible the flat roof needs to be
  • a seal coat, or waterproofing membrane

How you go about sealing a flat roof depends on the material you intend to use: this choice will also affect the effectiveness of the insulation and the durability of the waterproofing. The main roof waterproofing membranes are:

  • double-layer bituminous waterproofing membrane (asphalt or coal-tar pitch)
  • monolayer EPDM rubber seals (Ethylene-Propylene-Diene Monomer)
  • liquid membranes

Additional features such as solar panels or green roofs are also an option provided there is a suitable supporting structure.

a roof terrace

Particular attention should be paid to disbonds and tears, particularly around the skirting. Periodic roof inspections should be conducted to extend the durability of the roof covering, mainly at susceptible points (e.g. flashings, joints, covering, edge turn-ups).

Waterproofing & sealing

Depending on the type of roofing materials and waterproofing used, laying a flat roof will require, in addition to conventional roofing tools:

  • welding equipment, blowtorch or hot air gun or welding robot
  • pressure rollers
  • adhesive sealing strips

while waterproofing

As with all jobs at height, it is important to ensure safety when waterproofing. For this purpose, and in accordance the with standard EN 13 374 class A, the work area must be protected with railings that satisfy the requirements of NF P93-355: these include high rails, safety nets, and metal bollards positioned no more than 1.5 m apart, and held in place using reversible clamps or another suitable fixing system.

As a registered member of the CSFE (French Chambre Syndicale for Waterproofing), Dimos helps professionals not only to get the right equipment, but also to ensure safety on site.

Our solutions of Collective protection