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Testing times

Thorough and extensive testing and developing is vital before any Lafarge Roofing product is supplied to an end user

The great storms of 1987 and 1990 affected more than one million roofs in the UK, but not a single properly fixed Redland roof was damaged. Before any Lafarge Roofing product is offered to architects and specifiers, it undergoes a stringent testing process to establish its fitness for the purpose for which it was intended and its durability.

'Roofing products must be able to withstand the ravages of time and exposure without being degraded, ' explains Nigel Cherry, group head of product development. The group's expertise has also led to the development of new products, and new roofing systems.

Equipped with such extensive experience and research, the group has worked for many years with internationally recognised research bodies throughout the world, including BRE in the UK, and with standards organisations in the UK, US and Europe to establish sensible fixing practices.

It has collaborated, for example, on the Euro-Code for wind loading, and on CEN standards for wind uplift, driving rain, external fire performance and concrete/clay tiles. In numerous instances the group has been the driving force behind new standards and has supplied much of the technical expertise to develop them.

The basis of functional and durability testing is a thorough knowledge of the climatic conditions which will be experienced by the product, and of the behaviour of past, current and new products in a range of climates.

Many years ago, Redland established a string of international weather stations and weathering sites in various climates around the world. It has collected weathering data from this worldwide network since 1985, and has used it to calibrate tests that predict how products will perform. Each weather station gathers a wide variety of information. There are instruments to measure wind speed and direction, for studying wind loading and ventilation, and instrumentation to study driving rain. Air temperature, UVA intensity, and the rainfall pH are also measured, to predict the performance and durability of coatings and plastics.

Some weather stations, such as the UK site at Horsham, also act as weathering sites for tiles. As well as having their natural weathering assessed over time, tiles are measured for temperature and are fitted with wetness-time sensors and weight sensors to reveal their performance in freeze-thaw conditions. The weather stations and weathering sites are facilities unique to Lafarge Roofing and are not available elsewhere. In recent years, Lafarge Roofing has installed custom-built automatic weather stations that have greatly enhanced predictive methods. Information is transmitted daily via automatic computer links.

The size and scale of the Lafarge Roofing testing facilities at Crawley, West Sussex, are unique to the roofing industry. Lafarge Roofing tiles and roofing products come from all over the world to Crawley to be tested. A key - and unique - part of the testing system is the driving-rain/wind tunnel, which was commissioned in 1990 at a cost of £1.4 million. It allows a whole system - comprising tiles together with their supporting battens and underlay - to be tested for resistance to driving wind and rain penetration.

The risk of driving snow penetration can also be assessed. A sample of the roof system is mounted in the tunnel and subjected to wind, rain and suction. A separate rig predicts the resistance of the tile system to wind uplift.

Products and systems are also tested for fire performance, susceptibility to damage in transit, condensation and ventilation, energy implications and impact damage (a tile profile must be designed to resist likely loads, particularly at the edges, caused by people walking on the roof during construction or for access and maintenance). Laying trials are also carried out to check for any problems, to ensure that new products are 'user-friendly'.

Durability testing

The laboratory at Crawley has a wide range of test installations that accelerate the natural weathering process so that durability of new products can be predicted. An individual test programme is specified for each new product, based on functional requirements and weathering factors. Specific tests include the following:

Sunlight, ultraviolet (UV) and accelerated weathering. Sunlight degrades plastics and polymer coatings. Although UV comprises only five per cent of sunlight, it is the most damaging component, particularly in damp and wet conditions with high or fluctuating temperatures.

Acid-rain and accelerated testing. Acid rain is caused by pollutants from the burning of fossil fuels. The laboratory has established that concrete tiles can resist acid rain for the lifetime of the building (the surface will become etched and will change slightly in appearance after a time but without suffering significant damage). Acid-rain testing has been the key to the development of many new products; 30 years' exposure can be simulated in less than a month.

Freeze-thaw resistance. A continuous cycle of freezing and thawing can cause damage to building materials through expansion of rainwater as it turns to ice. Internal microcracks accumulate to produce visible swelling and cracking.

Rapid changes and extremes of temperature. In some climates, products can be subjected to changes in temperature of 50infinityC in minutes or even seconds. The repeated cycling of temperatures can cause microcracks to develop and propagate.

Working overseas

The group has developed a 'cool roof ' assembly for use in hot climates. The roof is environmentally friendly; compared to traditional tile or shingle roofs, the cool roof reduces heat flow, saving energy by reducing or obviating the need for air conditioning. It also reduces running costs for the owner.

Even without air conditioning, the cool roof reduces heat flow by 84 per cent. The assembly comprises:

A tile roof covering, light grey rather than red in colour, to reflect heat. Tiles are laid on battens and counter battens to create a larger than usual air gap, which is ventilated at eaves and ridge through special hip and ridge tiles. Both hip and ridge tiles are dryfixed to increase ventilation.

Below the tiles is a radiant barrier to reflect solar radiation. It is laid on a solid plywood deck which is cut back at the eaves to vent the loft space.

Design advice

The group offers a design advice service for individual roofs both in the UK and overseas. Architect Ria Smit had designed a housing project at Zeewolde in the Netherlands, with a complex roof in which rows of tiles are supported on sloping rather than horizontal battens. Obviously the tile and roofing system had been tested in the traditional form, and the architect was justifiably concerned that rain and wind penetration might occur. Samples of tiles laid with battens at different slopes and to different roof pitches, were tested in the wind tunnel. As a result a safe laying specification was developed for this novel building.

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