Reinforcing the GRP Message

Andy Fell of Hambleside Danelaw explores how housebuilders and developers can avoid the common pitfalls of flat roofing by specifying glass reinforced polyester (GRP), explaining its various benefits.

How many times have you heard it said: ‘flat roofs never last more than 10 years’?

Even roofing materials manufacturers have to admit that ‘flat’ roofs are not always seen as being attractive, and can be perceived by some as troublesome.

There are many common pitfalls when specifying and installing flat roofs that must be addressed to avoid these issues, including:

  • Inadequate or inappropriate design
  • Low levels of insulation
  • Inadequate ventilation
  • Unsightly edge details
  • Poorly sealed junctions and abutments
  • Fitting by under-trained roofers

Attractive and reliable
What most specifiers, housebuilders and owners want is a good-looking, reliable roof. It doesn’t seem a lot to ask, does it?

Sometimes however, what they get is a disappointing, problematic and not to mention expensive liability. Poorly installed and badly finished roofs not only put a property at risk, but can also let down its appearance, possibly leading to expensive running repairs and reduced property value.

How many times have you seen an uneven felt roof which looks like a child has installed it?

Poor details in roof construction are among the most common causes of water ingress into a building – as with many roof covering systems, the detailing has to be decided upon as the job progresses, leading to solutions which have not been fully thought through.

GRP Roofing
Glass reinforced polyester (GRP) is a robust, lightweight material, which is naturally watertight, aesthetically pleasing and has great longevity. Its bulk strength and weight are better than many metals, meaning that it can be readily moulded into complex shapes and can be used for a wide variety of roof coverings.

The material also benefits from good fire retardancy, is easy to handle, and, as it is UV resistant, is ideal for roofing installations. Being a flexible material, it is versatile and easy to repair, and – providing it is offered by a responsible manufacturer – can be fully recyclable at the end of its service life.

GRP was initially developed for widespread applications by the British military during WWII. The plan was to use GRP for several applications, including building the minesweeper fleet because of its light weight, strength, and lack of magnetic footprint. Later, the benefits of GRP were recognised as ideal for a variety of uses across the boat building, motor manufacturing and construction industries.

As the name suggests, GRP is produced by combining glass fibres with thermosetting polyester resin consolidated under strictly controlled factory conditions. The glass fibres are embedded into the resin with several layers of fibres facing in different directions, allowing the stiffness and strength of the finished material to be controlled.

GRP in ‘flat’ roofing
There are two main types of system where GRP is specifically used as a ‘flat’ roofing membrane. One of the most commonly used systems is ‘wet-lay’, where the roof substrate is effectively used as a mould for an in-situ lamination in a similar manner to boat building.

The proven alternative to ‘wet lay’ is a component-based membrane system where all the products involved are pre-manufactured under closely controlled factory conditions, thus improving the speed and flexibility of installation.

For both wet lay and component-based systems, a correctly installed GRP roof should have a service life of at least 30 years.

Environmental benefits
As GRP is safe to use in greywater systems and does not release any chemicals once installed, it is a favoured material for eco-friendly housing, both ‘green’ and ‘blue’ roof waterproofing.

At the end of its long service life, GRP can also be broken down into its component elements, which can then be recycled into new materials, saving the customer money while benefitting the environment.

A major benefit of GRP when used as a roof waterproofing membrane is the additional ability for the material to be refurbished in-situ towards the end of its service life, doing away with the financial and environmental costs associated with re-roofing.

Andy Fell is national sales manager of Dryseal at Hambleside Danelaw