Definitions

For the purposes of this Technical Booklet the following definitions apply – Air permeability – the air leakage rate in cubic metres per hour per square metre of envelope area (m3/(h.m2)) at a pressure difference of 50 Pascals. Air tightness – a general descriptive term for the resistance of the building envelope to infiltration with ventilators closed. The greater the air tightness at a given pressure difference across the envelope, the lower the infiltration. Automatic control – where a ventilation device is opened and closed, switched on and off, or its performance adjusted by a mechanical or electronic controller which responds to a relevant stimulus. That stimulus is usually related to the humidity of the air in a room, pollutant levels (e.g. carbon dioxide concentration in a room), occupancy of the space (e.g. using a passive infra-red motion detector) or pressure difference across the device (e.g. due to the wind outside). Background ventilation – is ventilation by means of a small ventilation opening designed to provide low rate controllable whole building ventilation (e.g. a trickle ventilator), usually not less than 1.7 m above floor level. Basement (in relation to dwellings) – a dwelling, or a usable part of a dwelling (i.e. a habitable room) that is situated partly or entirely below ground level. Bathroom – a room containing a bath or shower whether or not it also contains other sanitary appliances. Cellar – part of a building that is situated partly or entirely below ground level and that is used solely for storage, heating plant or other purposes but not for habitation. Closable opening – a ventilation opening which may be opened and closed under either manual or automatic control. Common space – a space in a non-domestic building where people are expected to gather in large numbers such as shopping malls, foyers and similar common spaces but does not include spaces used solely for circulation. Continuous operation – a mechanical ventilation device that runs all the time (e.g. mechanical extract ventilation (MEV) and mechanical ventilation with heat recovery (MVHR)). The air flow rate provided by the mechanical ventilation need not be constant but may be varied, under either manual or automatic control, in response to the demand for pollutant or water vapour removal. Design air permeability – the value for air permeability selected by the designer for calculating the Dwelling carbon dioxide Emission Rate (DER).