04 Jun 2015

Drainage: Come rain or shine

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Often when starting a new build project, rainwater and eaves systems are not particularly high on the agenda, but ignoring correct specification can have catastrophic effects. Here, Tony Wereszczynski, Technical Director of rainwater system specialist Alutec looks at how self-builders can get it right, taking into consideration the technical requirements, performance, cost and aesthetics.

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Self-builders already account for a significant proportion of the new housing market –7-10% or approximately 12,000 homes per year – and with government plans to double the size of the market over the next decade, this figure is only set to increase. But for too long the aspirations of ordinary people to build their own home have been thwarted by barriers and red tape. With so much legislation to adhere to, it makes sense to seek guidance from specialist manufacturers that can provide advice on all aspects of the different planning and design stages, to ensure the correct rainwater and eaves systems are chosen for the property.

With real potential for lasting and expensive damage if incorrectly specified, rainwater systems are a vital part of the building’s external envelope. There are several key factors that need to be taken into account when assessing the suitability of a rainwater system and ensuring it satisfies Building Regulations and British Standard requirements.

The process should involve calculation of the roof area and selection of the appropriate rainfall intensity, to establish peak flow rates for comparison with the gutter capacity. Reference should be made to BS EN 12056-3: 2000 which provides detailed information on rainfall throughout the UK, by geographical location and frequency of occurrence.

Another important issue is the capacity of each system, which varies depending on profile, size and whether the gutter is fitted level or to a fall. For design purposes, eaves gutters are normally sized to ensure the calculated run-off does not exceed 90% of the gutter capacity.

Climate factors

Looking forward is the key. Climate change is affecting rain patterns throughout the UK to such a degree that current metrological data on rainfall intensities cannot be relied upon. Therefore a higher degree of rainfall, in particular flash storms, must be taken into account when designing a roof drainage system. Indeed, with a run of severe winter weather over the last few years, the sheer weight of snow sliding from roofs caused countless damage to gutter systems throughout the UK, which should be taken into consideration and appropriate solutions allowed for. Another factor that should be considered is the inclusion of a leaf guard system if the property is in the vicinity of trees, to ensure the gutters are always clear and not overflowing, which can lead to blockages.

Potential savings can be high, predominantly linked to the ancillary costs that can be avoided if the design is right. For example, careful thought needs to be given to the position of gutter outlets, bearing in mind the flow characteristics of the rainwater system. It may be possible to reduce or eliminate the number of rainwater pipes, underground drains and manholes required, thereby introducing economies through good design.

Having said all that, it’s important to remember that while rainwater and eaves systems have an important functional role to play in the performance of a building, this does not mean self-builders must limit themselves when it comes to the design opportunities they offer, as all aspects of a building’s exterior can contribute to its ‘kerb appeal’.

Aesthetic considerations

Depending on the character of the property being built or renovated, the overall aesthetics of the system and how this fits in with the style of the building will be very important. Rainwater systems for example, are available in a wide variety of profiles so it’s worth considering how these will complement the other design elements within the building’s external facade. For instance, the sleek lines of a contemporary designed property work well with more angular shaped rainwater systems, so it’s worth looking out for square profiles that provide high capacity and a minimalistic modern appearance.

Conversely, for properties reflecting a more traditional look, cast iron styles are a popular choice and - certainly for period refurbishments - there comes a requirement to replace like for like. There’s no doubt that by using cast iron for this type of work, the initial installation will look beautiful. However, the regular re-painting that the system will ultimately require is time consuming and expensive, not to mention the installation difficulties that come with such a heavy material.

Many self-builders are now seeking modern, low-maintenance alternatives to period building products, either for refurbishment projects or traditionally styled new-builds. Aluminium fits this requirement perfectly and is being used more and more, as people become increasingly aware of its benefits over other materials. For example, Alutec has recently introduced a Tudor downpipe system, designed to classic aesthetics with twenty-first century performance standards, as well as longevity and durability associated with an aluminium solution.

However, there is no need to stick to traditional colours and self-builders should bear in mind the eye-catching effects that can be created with more unusual choices. If opting for a brightly coloured system, look for products that benefit from an architectural grade polyester powder coating, this results in a durable, colour stable decorative finish that will last for the design life of the product.

Technological advances

Eaves systems are another fixture that can be used to inject some character into the building’s exterior but are an area that is often overlooked by self-builders, as the choice of products has traditionally been somewhat limited. Coloured PVC systems are costly and short lived, with a lifespan of only 10 years. Sheet aluminium systems offer better durability but are complex to handle and require a specialist contractor to install them, pushing the costs up for the self-builder.

However, recent technological advances have enabled the creation of truly flexible systems that offer a number of benefits over plastic or sheet aluminium alternatives.

Alutec’s Evoke fascia and soffit range, for example, is a lightweight system that uses aluminium composite panel (ACP) to offer greater durability, longer colour fastness and easier installation than other systems currently available. What’s more, the Evoke system is easy to handle and can be modified on-site using conventional carpentry tools and skills, meaning specialist contractors are not required.

With such a wide range of creative options available in the market, rainwater and eaves systems do not need to be an after thought but instead can play a fundamental part in setting the character of a building’s exterior. Whatever the case, it’s always worth seeking advice from a specialist manufacturer’s technical team for specification guidance and support to ensure these important building elements offer the best in terms of performance and aesthetics.

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