Section 2: Dangerous Substances (Including Radon & Landfill Gas)
Prior to commencement of works on site suitable site investigations should be under taken to determine if there is any contamination. The investigation should include but is not limited to determining the previous uses of the site which can give an indication as to whether the site will be contaminated or not.
A more detailed guide on how to undertake site investigations is contained within BS 5930: 2015 - Code of practice for ground investigations. Site investigations should be undertaken by a suitably qualified competent person.
While not a comprehensive list, some of the signs of possible contamination have been listed below:
Unusual smells – This could indicate the presence of harmful gases or other matter on the site.
Drums/Containers – This would require further investigation as to what is/was contained in the drums. They may have been empty when left on the site or may have leaked into the site.
Vegetation – If there is no vegetation growing on site or only growing in specific locations it may indicate soil that is contaminated and not compatible with growth.
Unusual sightings – If you notice strange colouration on site or possible dumping/landfill further investigation should be undertaken to determine if there is contamination.
Table HC1 - Sites likely to contain contaminants - Extract from TGD C
Table HC2 - Possible contaminants - Extract from TGD C
Radon is a naturally occurring radioactive gas which enters buildings from the soil. If it accumulates within the building to a certain concentration it can be deemed to be a potential health hazard.
The National Reference Level (NRL) for long term exposure to radon within dwellings is 200 Becquerels per cubic metre (200Bq/m^3^).
The Radiological Protection Institute of Ireland (RPII) undertook a national survey on the radon levels within existing houses and based on this survey they prepared reference maps which indicates high radon areas. While it is estimated that 10% or more of dwellings within areas of high radon will have concentrations in excess of the NRL dwellings with high levels of radon are not confined to these areas and can occur anywhere.
At a pre-construction stage it is not possible to predict with accuracy the concentration of indoor radiation likely to occur in a proposed dwelling.
Appropriate measures should be taken at the design and construction stages to limit the risk of radon levels within the building exceeding the NRL.
Maps showing the estimated percentage of houses above the National Reference Level for dwellings for each 10km grid square are presented in Maps 1 to 5 at the end of this section, which are prepared by the RPII and provided in Technical Guidance Document C. Any queries in relation to these maps should be directed to the RPII.
The RPII can be contacted at 3 Clonskeagh Square, Clonskeagh Road, Dublin 14, Tel 01-2697766 or at http://www.rpii.ie
High Radon Areas
For normal non-complex dwellings protection from radon can be achieved by providing a fully sealed membrane having a low permeability over the full footprint of the building. A means of extracting radon from the substructure should also be provided i.e. sumps with connecting pipework, standby radon sump or other appropriate certified system.
Areas other than High Radon Areas
Should it be determined to be required after construction a means of extracting radon from the substructure should be provided.
Radon Prediction Maps
The below maps which have been prepared by the RPII give an indication of radon levels in specific location.
Diagram HC3 - Index map of Ireland - Extract from TGD C
Diagram HC4 - Radon prediction map for the North West of Ireland - Extract from TGD C
Diagram HC5 - Radon prediction map for the North East of Ireland - Extract from TGD C
Diagram HC6 - Radon prediction map for the South West of Ireland - Extract from TGD C
Diagram HC7 - Radon prediction map for the South East of Ireland - Extract from TGD C
The membrane to be used for radon protection should be suitable for its use and should be certified as such by an approved body. Membranes used to safeguard against radon ingress are normally provided in place of damp proof membranes.
While many radon barriers are Low Density Polyethylene (LDPE) membranes they can also be of other approved materials. Table 3 of Technical Guidance Document C gives guidance for the minimum performance levels for LDPE membranes. The testing of other materials may differ from that of LDPE membranes however the performance levels should be equivalent to those detailed in Table 3 of Technical Guidance Document C.
Table HC3 - Minimum performance level for LDPE radon proof membranes - Extract from TGD C
Sufficient care should be taken when installing radon barriers to the membrane achieve a gas tight seal, all service penetrations should be adequately sealed. The radon barrier should be installed only by persons who have received the appropriate training, appropriate allowances should be made for settlement to ensure it does not cause damage to the membrane. Prior to and after the installation of the radon barrier all persons on site should take care to ensure the membrane is not damaged.
Where radon sumps are provided the hardcore layer should be well compacted, clean and dry. After the compaction process the hardcore layer should be gas permeable, if there are any obstructions beneath the floor slab it could lead to the standby sump becoming less effective. Where obstructions are present beneath the floor slab perforations may need to be provided in the rising walls or alternatively it may be necessary to provide standby radon sumps to each compartment with interconnecting pipework. Typically, one radon sump will serve an area of approximately 250sqm for a distance of 15m from the sump.
“Radon in Existing Buildings – Corrective Options” (2002) provides further guidance on the number of standby radon pumps required, the design and location of in addition to the design of the associated pipework.
Radon Sump Pipework
The pipework associated with radon sumps should discharge externally above ground level or within the attic space and should be capped. External pipes should be suitable protected to ensure there is no ingress of rainwater, small animals or rodents.
Pipework associated with the radon sumps should be clearly identified including identification of its purpose, a marker plate should be erected adjacent to the pipework on a permanent structure.
Should a gas extraction system be considered necessary from the sub-floor this can be achieved by extending the pipework and installing and activating a fan. The extract terminal should be located to ensure the installation of additional pipework and a fan can be reasonably easily fitted without causing any major obstructions.
While the guidance provided above is intended to keep radon concentration levels as low as is possible for the area in question it does not guarantee that the levels will be reduced below the National Reference Level. Radon levels should be measured when the building in use if the levels are in excess of the NRL remedial action should be taken and the levels should be measured again once complete.
Where a dwelling is to be constructed on or near a site containing landfill guidance should be taken from the “Protection of New Buildings and Occupants from Landfill Gas” with respect to the design and construction of the buildings.