Boosting cavity wall performance with Cavity Trays.

Cavity wall thermal calculations are not based on water saturated bricks but on dry bricks or minimally wet bricks with a water content of five per cent. This is fine when considering performance during the summer months, but not so in winter. As an outside skin becomes wetter, its conductivity increases and can double upon saturation. The situation deteriorates further due to evaporative cooling, which can really accelerate heat-loss from the structure.

It’s also worth remembering how some masonry is tested to BS 4315. This involves spraying water onto a given area at a rate of 2.5 litres per minute. Upon completion of the 48-hour test, it is not unusual to read: ‘the bricks indicated very low-level rates of rain penetration.’ It is often not realised that the water spraying is noncontinuous. It lasts just one minute, followed by a half-hour pause, after which there is another one minute of spraying and so on. If it only ever rains in your area for exactly one minute followed always by half an hours’ drying time, then perhaps the Standard is meaningful, albeit not realistic of the climate experienced in the UK.

For specifiers there are two beneficial considerations. First, identify appropriate cavity tray specification to manage water arrestment and swift water evacuation. The acceleration of thermal loss diminishes, the faster masonry skins become dry. Second, consider Continuity Closers featuring L-shaped insulating cores that wrap across the surface of partial-fill cavity insulation. These block the heat-loss path often witnessed where ordinary closers and cavity insulation are meant to abut – but don’t.

Please specify clearly to secure benefitting accompanying warranties. The Cavity Trays Technical Manual can be delivered to your door along with a complimentary 2022 year-planner.

Cavity Trays Ltd.
enquiries@cavitytrays.co.uk
www.cavitytrays.co.uk