For the Irish market opening areas for background ventilators are specified in terms of equivalent area. The equivalent area of a ventilator is always less than the free area and is a better measure of the airflow performance of a ventilator. The more complex the airflow path through a ventilator, the greater the difference between equivalent area and free area. Equivalent area is measured in accordance with the method specified in I.S. EN 13141-1:2004.

If the equivalent area cannot be established then the free areas specified should be increased by 25% where free area of ventilators is used instead.

For dwellings one of three strategies can be used to meet the requirements.
• Continuous mechanical extract ventilation
• Mechanical ventilation with heat recovery
• Natural ventilation with specific provision for extract ventilation
• Other approaches to ventilation provision may be adopted provided the requirements of Regulation F1 are met.

Should be located, as far as possible to avoid draughts, e.g. more than 1.75 m above floor level.

All background ventilators should be tested to I.S. EN 13141-1:2004 and installed to manufacturers’ instructions.

For a dwelling with a single exposed façade, e.g. an apartment with only one exposed side, natural ventilation should be provided by the use of high and low background ventilators. The area of high-level ventilators should be as set out in Table 3 with an equivalent area of low-level ventilators installed. There should be a distance of level of at least 1 metre between vents.

Two habitable rooms may be treated as a single room for ventilation if there is an area of permanent opening between them and a wall or window ventilator having an equivalent area not less than 8,000 mm2.