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Drainage matters

Sapphire Balustrades, a leading UK manufacturer of balcony and balustrade solutions, considers the most frequently asked questions when it comes to designing a drainage solution for a balcony project.

Different balcony structures have different drainage requirements. Concrete balconies, for example, tend to be treated like a flat roof and are normally finished with a waterproof membrane, drainage outlet or overflow pipe.

Building Regulations
Any water collecting on a balcony deck, either from rainfall or from watering container plants, should be addressed in the design of the balcony to ensure it doesn’t drip onto the balcony below. With this in mind, drainage of balconies is covered by Building Regulations and industry guidance. Approved Document H3 of the Building Regulations requires adequate provision for rainwater to be carried from the roof of the building but does not state whether balconies are considered part of ‘the roof’.

Industry guidelines
NHBC guidance (section 7.1 ‘Flat roofs and balconies’) states that balconies shall have adequate rainwater disposal to a suitable outfall but does not go into detail about drainage options.

Given the lack of clear guidelines, Sapphire strongly recommends that Building Control and NHBC inspectors are consulted at an early stage of a balcony project to ensure the proposed solutions meet with their approval.

Decision factors
Having considered the legal requirements, let’s take a look at the main issues and solutions when choosing a balcony drainage system.

Firstly, there is the question of cost. Free draining balconies are the lowest in cost. The addition of a drip tray typically adds around 10%. Incorporating positive drainage to a Rain Water Pipe (RWP) typically adds a further 25% and also makes the construction significantly more complex.

Appearance is another important consideration. The rather ‘industrial’ look of free draining balconies can be improved by adding a soffit/drip tray. Balconies draining to a RWP need to be deeper to accommodate pipework so can look chunkier

Safety must also be considered in any decision. The risk of hot liquids falling through the balcony deck onto residents below can be reduced by a drip tray or RWP.
Last, but not least, there is the issue of façade staining. The use of positive drainage is likely to reduce the risk of water running down the façade and causing staining.

Decking options
Another question we are often asked at Sapphire is whether the choice of balcony deck has an impact on drainage and the answer is yes. Grooved decking boards are commonly used as a surface. Experience has shown that the majority of rainwater falling on the decking will run along the grooves and drip off the end of the board. It is, therefore, better to run decking parallel with the building line, otherwise there can be a substantial amount of water dripping off adjacent to the façade, increasing the risk of staining or water penetration.

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