Cassette® balconies have soffits individually fixed to the rafters at typical 400mm centres. Each soffit has a gradient, usually sloped to the front of the balcony, so that rainwater will flow towards the front of the balcony, where it can freely drain.
Because each soffit allows the water contained within it to drain across the front edge, rainwater can be dispersed quicker and is less likely to puddle. This also makes the balcony less likely to block, like concrete, or steel frame balconies which depend on an individually, or small number of spouts.
The addition of a drip tray typically adds around 10% to the cost of an undrained balcony. This is well worth considering as this has significant benefits over open balconies with no soffits at all. Incorporating positive drainage to a Rain Water Pipe (RWP) typically adds a further 25% to the cost, and also makes the construction significantly more complex.
Both NHBC and other warranty provider’s schemes expect there to be some form of rain water management and therefore controlled drainage solutions using soffits which do this through draining the water consistently across the front edge of the balcony are typically required. This is usually adequate even when balconies are over 6sqm.
Previously, we found some clients choose to clad the underside of the balcony with decking to match the top surface. This would normally be in a free draining situation where water falls between the deck boards. This has become less common recently, as it doesn’t give the longevity of properly coated aluminium soffits and is often not a cost benefit despite having a lower perceived value.
Unfortunately there has been a significant number of balcony fires in the UK during 2018. A number have spread rapidly because of there being either no soffits or combustible soffits. Read more about the effects of balcony fires in our whitepaper.
British standards are set to change soon and are expected to steer away from positive drainage and towards managed. Contact us for more information.
We created the video below of a NHBC scheme where the smaller balconies are free draining to the front and those over 6 square metres are pipe drained to RWP’s. You can see a clear comparison of how balconies drain using different forms of soffits on the balconies, and the difference is very little.