Regulations: Underfloor Ventilation in Republic of Ireland
Providing a building with adequate and effective underfloor ventilation is an essential foundation for the prevention of moisture and damp and the build-up of dangerous gases, such as radon. For your convenience, we have outlined extracts from the following regulations:
- Building Regulations, Technical Guidance Document C (1997 edition incorporating 2020 amendments).
- For detailed guidance, refer to the full technical document available to download here.
Technical Guidance Document C: Site Preparation and Resistance to Moisture
Suspended Timber Ground Floors
3.1.8(b): A suspended timber floor next to the ground should be built as follows:
- There should be a ventilated air space measuring at least 75 mm from the concrete to the underside of any wall plates and at least 150 mm to the underside of the suspended timber floor (or insulation if provided).
- Each external wall should have ventilation openings placed so that the ventilating air will have a free path between opposite sides and to all parts. The openings should be large enough to give an actual opening of at least equivalent to 1500 mm² for each metre run of wall.
- Any pipes needed to carry ventilating air should have a diameter of at least 100mm.
Suspended Concrete Ground Floors
3.1.9: Suspended concrete ground floor with ventilated voids – This type of floor should be built:
- (b) with a ventilated air space measuring at least 150 mm clear from the ground to the underside of the floor, and
- (c) with ventilation openings in each external wall placed so that the ventilating air will have a free path between opposite sides and to all parts. The opening should be large enough to give an actual opening of at least equivalent to 1500 mm² for each metre run of wall.
- Note: Sub-paragraphs (b) and (c) apply where there is a risk of explosive gas mixtures accumulating in voids under the floor. The height of the ventilated air space may be reduced where proprietary void formers are used.
- Position ventilation clear of hard landscaping and vegetation.
- Where flooding is a risk, consider using Rytons Periscope® Vertical Extension to raise the height of the Periscope® by up to 1m above ground level, this may prevent low-level flooding and protect the property for longer against higher flood water. Note: Flood water deeper than 1m should be allowed into the property to relieve pressure on the walls.
- Specify Rytons underfloor ventilators by name. Alternative products may have lower rates of ventilation which could leave the sub-floor under ventilated. Find NBS specifications here.
- Rytons Periscope® Underfloor Ventilator with Multifix® Air Brick is a plastic unit and therefore is not suitable for use within the external walls of high-rise buildings requiring non-combustible materials. For a compliant alternative, see Rytons A1 Fire-rated Periscope Underfloor Ventilator.