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Testing for rain noise

Testing for rain noise

SRL ensures that lessons at The Orchards School, in Stretford, are not disrupted with rain noise on its roof, thanks to the technical services firm’s rain noise test rig, that measures the potential level of rain noise on a roof, prior to construction.
Rain in the UK is as ubiquitous as tea or black taxis. Thanks to its location in the Atlantic Ocean, the British weather can change on an hourly basis making it surprisingly unique, despite its often-gloomy appearance. Because weather is constantly changing, you can guarantee that rain is never too far away.
When rain lands on a surface like a roof, it behaves like the skin of a drum. The impact of the rain, like a drumstick, causes vibrations on the roof surface which generates noise which can then be transmitted into the rooms below. If the roof is made of a lighter material, then the rain can cause greater vibrations which in turn generates more noise.
This noise is not a universal problem. If your room below is a warehouse, then rain noise rarely causes problems, but in a school or hospital, rain noise can disrupt lessons or prevent people from sleeping when recovering on a ward.
Rain noise was once relegated as a foot note in building design guides, if it was mentioned at all. Now there are several design guides, most notably the designs for schools, hospitals and offices, which give specific rain noise limits within different rooms. The level of allowable rain noise is usually dependent on how the room will be used.
This means that if you need to supply a roof to a school, hospital, or an office, you must be able to supply a roof which can meet these rain noise limits.

How is rain noise measured?
With unpredictable weather it is impossible to take reliable measurements of rain noise onsite during construction. Modelling rain noise is also extremely complex, so instead, the noise generated from a roof is measured in specialist rain noise test rigs, which SRL have in our laboratory in Suffolk.
Measurements are taken by creating standardised and repeatable ‘rain’ which falls from a water tank onto the test sample and the resulting noise is measured within in a test room below.
The SRL rain noise test rig is compliant with BS EN ISO 140-18:2006 and is UKAS accredited. We can facilitate the construction of the roof on the rig or a pre-assembled sample can be lowered into place. We also have a working platform on all sides to aid construction of the sample.
Ceilings play a crucial part in attenuating rain noise. Schools will have different rain noise requirements in each room, which is often achieved by using different ceilings according to the amount of rain noise insulation required. SRL have a false ceiling grid installed in the test room so we can efficiently test your roof with a combination of different ceilings.

Case study
Project: The Orchards School
Main contractor: Conlon Construction
SRL developed the acoustic design for The Orchards School in Stretford. The school caters for up to 98 pupils with Special Educational Needs, which meant that during the design, a more stringent rain noise criterion needed to be achieved, within classrooms under BB93 Acoustic design of school’s requirements. The building design utilised a prefabricated timber roof cassette, however, the ceiling/roof construction had not been tested for rain noise.
Rain noise predictions for similar constructions were not available so Conlon Construction commissioned a rain noise test at SRL’s Laboratory. The tests demonstrated that the proposed roof/ceiling construction could meet the BB93 rain noise requirement without any further attenuation avoiding overdesigning the roof and ceiling and saving the project additional budget.