Ventilating Under Floors – Your Choices Increased
The Building Regulations require voids under suspended concrete floors to be ventilated and for the ventilated space to measure not less than 150mm from ground level to the floor underside or to any insulation under it. Airflow into and out of the void is normally required to be from two opposing external walls. These should have ventilation openings placed so that the ventilating air has a free path between opposite sides and to all parts of the floor void. Cavibricks to provide the airflow are usually positioned under dpc level and are required to support airflow of not less than either 1500mm²/m run of external wall or 500mm²/m of floor area, whichever gives the greater performance.
Where the external ground level is high and prevents ventilation straight through a wall, cavibricks can be built in at higher level and airflow directed to the lower level under the floor via a connecting cranked sleeve called the Type TAV – Telescopic Adjustable Ventilator.
Type TAV Telescopic Adjustable Ventilators expand and contract by up to five brick courses, with the expanding section located within the cavity of the wall. Where a greater height difference is called for, there are now both vertical and horizontal extension sections to broaden the designer’s options.
Extension sections are manufactured in lengths of up to 1200mm, and provide compatible conduits to ensure airflow may flow unobstructed. Whether the extensions are required because of the ground levels, the wall thickness or the location of an isolated void, the requisite airflow to comply with Building Regulations can be addressed.
The inner surfaces of the extension ducts have a smooth gloss finish, to lessen friction and aid laminar flow.
Attachments are also available to permit Type TAV ventilators and cavibricks to be connected to nominal 100/105mm round plastic pipe, should the designer consider it appropriate for connection to remote or isolated voids.
All Type TAV Telescopic Adjustable Ventilators are accompanied with a preformed cavitray that protects the top of the adjustable sleeve from acting as a bridge over which water might track towards the inner skin. Cavity Trays Ltd is the only manufacturer providing a protective cavitray as part of the Type TAV product package.
Whilst the Type TAV can be fitted with a wide range of airbricks, Cavity Trays Ltd recommends the approved cavibrick which is available in a range of masonry merging colours. Unlike alternatives, cavibricks incorporate integral deflectors and a waterdam upstand that guards against wind-driven rain that might enter the ventilation louvers during severe conditions..
For more information refer to The Book of Wise Decisions volume 40 2012 edition and Protecting the Building Envelope volume 22. Both available free of charge from Cavity Trays Ltd, upon request.