Steve Cleminson, technical manager, SIG Design and Technology, on the best ways to prevent leaks in flat roofs

In association with

When a flat roof develops a problem such as ponding, cracks or blistering, the roofing contractor normally gets the blame. But nothing happens in isolation. Preventing costly leaks relies on everyone, from client to installer, doing their job right at every step.

Investigate the options
Rather than just negotiating hard on price, clients should decide what they want from the job and do some research to investigate the different options in order to get an economic fit for the approach they prefer.

Get the design right
I still come across architects who believe flat roofs are flat. Flat roofs should be designed to be free draining and at a minimum fall of 1:40 to achieve a minimum of 1:80 when taking into account building tolerances, mid-span deflections etc. This is in accordance with the minimum requirements identified in BS 6229:2003 (currently under review). Designers should feel free to design at more than the minimum and should design for a realistic, reasonable maintenance regime.
Ponding water can cause major problems, especially in winter, because of temperature variations between the ponds and adjoining dry areas. This can lead to cracking. Getting water off the roof is therefore essential in maximising the leak-free life of products and thus minimising water ingress due to defects or damage. It is also essential for the design to resolve 2D or 3D interfaces with other building elements before installation starts.
Some manufacturers are happy to accept ponding water on their products and believe it will not hinder the product’s integrity; however good practice and the BS 6229:2003 advise against it, and it can lead to moss growth and other issues.

Listen to the experts
Early engagement with the manufacturer and installer is key so that their specialist experience can be used. Roofers and manufacturers can provide a wealth of technical knowledge and experience and it’s wise to take their advice on board in order to minimise the risk of problems. Engage them as early as possible, ideally at design stage.

I still come across architects who believe flat roofs are flat. Flat roofs should be designed to be free draining and at a minimum fall of 1:40 taking account of building tolerances

Main contractor involvement
If main contractors have a working knowledge of specialist trades, they have a better chance of supervising a successful installation. A number of manufacturers, including SIG, are happy to offer training to main contractors’ supervisors/section managers or package managers which helps ensure management not only has some level of knowledge but also access to supporting expertise. Coordinating sequencing and access also minimises problems and allows the installers to do the best job they can.

Use properly trained installers
Training certification is insisted on by most of the credible suppliers – SIG, for example, will only sell products to installers who are accredited with its DATAC (Design and Technology Accredited Contractor scheme) training scheme. Membership of trade associations such as SPRA (Single Ply Roofing Association) or manufacturer/suppliers accreditation schemes are readily available to professional companies who buy into and demonstrate good working practices.

  • Temperature variations between ponded and dry areas can result in cracking.
    Temperature variations between ponded and dry areas can result in cracking.
  • Ponding water can also lead to moss growth and detritus build-ups, both harmful to a flat roof’s longevity.
    Ponding water can also lead to moss growth and detritus build-ups, both harmful to a flat roof’s longevity.

Don’t skimp on maintenance

Property owners tend to maintain what they can see and ignore what they can’t until there is a problem. We’ve seen deposits of leaves and moss that look like a green roof, as well as huge build-ups of guano and other debris preventing water draining away, or penetrating the membrane. This can dramatically accelerate the ageing of the installation.

To avoid this, property owners should have a proactive maintenance process  including regular inspections, maintaining the warranty, and ensuring accredited contractors undertake repairs with compliant products.

To find out more and download additional resources visit http://bit.ly/SIGRoofLines4