Two avoidable ventilation irregularities are still regularly witnessed on sites.
1.The frequency and distance of air bricks above ground level and the actual airflow provided.
2.Inadequate/obstructed exhausting of ground gases when construction takes place on contaminated land.
Approved Document C states 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 metre² of floor area.
The clay/concrete ventilation bricks photographed are too close to the ground. Despite appearances, the apertures provide minimal through-flow - little more than 20% of the ventilation level demanded. Thus, these as-built ventilation measures are 80% deficient.
In 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 - alternatives do not offer this combination.
If building on contaminated land and the external ground levels prevent gas from being horizontally outwardly exhausted from underneath the cavity barrier level, 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 level above barrier level and above ground level.
These solutions are designed and manufactured by Cavity Trays Ltd, the longest established tray manufacturer in the UK and the only cavity tray company awarded European Technical Approval.
www.cavitytrays.com
enquiries@cavitytrays.co.uk
