Cavity Trays explores how to avoid inadequate and non-compliant ventilation strategies
Cavibrick at higher level providing compliant airflow
Two avoidable ventilation irregularities are still regularly witnessed on sites. The first concerns the frequency and distance of air bricks above ground level and the actual airflow provided. The second, relates to inadequate/obstructed exhausting of ground gases when construction takes place on contaminated land.
Approved Document C states that suspended timber floors and suspended concrete floors, including block and beam, have a provision for ventilation on two opposing external walls of not less than 1500mm² per metre run of external wall or a minimum 500mm² per square metre of floor area.
Air bricks too low and providing insufficient ventilation
The clay/concrete ventilation bricks photographed are too close to the ground. Despite appearances, the apertures provide minimal through-flow – little more than 20 per cent of the ventilation level demanded. As such, these as-built ventilation measures are 80 per cent deficient.
By contrast, Cavibricks have an airflow rating of 7500mm². The requisite ventilation is easily achieved and Cavibricks also have deflecting louvres and an integral water dam – a combination of features not found on alternative products.
Harmonising barrier profile sleeve with Cavibrick
If the ground level prevents gas from being horizontally exhausted from underneath the cavity barrier when building on contaminated land, discharging above barrier level is possible by utilising compatible barrier profile sleeves. A gas-tight route is then possible vertically using a Telescopic Adjustable Cavivent, after which discharge can take place horizontally via Cavibricks at an appropriate position above barrier and ground level.
Higher level discharge in position, ready to receive Cavibricks
These solutions are designed and manufactured by Cavity Trays, the longest established tray manufacturer in the UK and the only cavity tray company awarded European Technical Approval.