Radon: Guidance on Protective Measures for New Dwellings
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Building Research Establishment Report Radon: guidance on protective measures for new dwellings Building Research Establishment Garston Watford WD2 ?JR Price lists for all available RRE publications can be obtained from: BRE Bookshop Building Research Establishment Garston, Watford, WD2 7JR Telephone: 0923 664444 BR211 ISBN 0 85125 511 6 ©Crown copyright 1991 First published1991 Reprinted with1992 revisions,1993 Applications to reproduce extracts from the text of this publication should be made to the Publications Manager at the Building Research Establishment CONTENTS Page Introduction 1 Protective measures 1 Primary protection 11 Suspended concrete floor 11 In-situ or ground-supported concrete floor 11 Secondary protection 11 Natural ventilation 11 Provision for mechanical ventilation 11 Provision for subfloor depressurisation 11 Detailed protective measures 11 Radon-proof membranes 11 Radon-proof cavities 12 Slip or shear planes 12 Lapping of membranes and trays 12 Reinforced slabs 13 Internal walls 13 Service penetrations 13 Condensation and cold bridges 13 Subfloor ventilation 13 Subfloor depressurisation 13 Passive stack subfloor depressurisation 15 High water table 15 Blinding 15 Party walls 15 Extensions 15 Garages 15 Monitoring of completed houses 15 Stepped foundations: additional points to consider 15 Further information 16 References 16 iii INTRODUCTION 'precautions shall be taken to avoid danger to health This report gives guidance for reducing the presence of and safety caused by substances found on or in the radon in new dwellings, and hence reducing the risk to ground to be covered by the building' and the occupants of exposure to radon. Interim guidance was Approved Document3 includes radon in the first issued by the Department of the Environment in contaminants described. It states that 'where a house June 19881. Since that time much experience has been or extension is to be erected in Cornwall or Devon, or gained of its application in practice. This report has parts of Somerset, Northamptonshire or Derbyshire been prepared to build on the experience gained and there may be radon contamination of the site and to provide a more comprehensive explanation of the precautions against radon may be necessary'. The principles involved. It provides practical details on Approved Document refers to the present report for methods of protecting new dwellings. Further research detailed guidance on where such protection is is however still needed and is continuing, and the necessary and for practical construction details. results will be incorporated into revisions of this report as they become available. PROTECTIVE MEASURES Radon is a colourless, odourless gas which is Radon enters a building primarily by airflow from the radioactive. It is formed where uranium and radium underlying ground. There are two main methods of are present and can move through cracks and fissures achieving radon protection in new dwellings: passive in the subsoil, and so into the atmosphere or into and active. spaces under and in dwellings (Figure 1). Where it • The passive system consists of an airtight and occurs in high concentrations it can pose a risk to therefore substantially radon-proof barrier across health. the whole of the building including the floor and walls (Figure 2). Whilst it is recognised that every house contains radon, some built in certain defined areas of the country • The active system consists of a powered radon might have unacceptably high concentrations unless extract system as an integral part of the services of precautions are taken. In the UK, the granite areas of the house. It will incur running and maintenance south-west England are of principal concern, but high costs for the life of the building. concentrations of radon are also found in some other parts of the country. Passive systems are to be preferred in new houses, although they may need to be supplemented by Requirement C2 of Schedule 1 of the Building secondary protection, involving for example Regulations 19912 for England and Wales states that underfloor ventilation or subfloor depressurisation. 6 Key to Ingress routes 1 Through cracks in solid floors 2 Through construction joints 3 Through cracks in walls below ground level 4 Through gaps in suspended concrete or timber floors 5 Through gaps around service pipes Figure 1 Routes by which 6 Through cavities in walls radon enters a dwelling Figure 2 Passive measures to Radon·prool prevent radon entry barrier It is impractical to assess the severity of a radon 2 New dwellings in Cornwall, Devon, Somerset, problem on a particular site accurately until the Northamptonshire and Derbyshire within the light building has been constructed and occupied, and shaded areas on the accompanying maps (Figures therefore precautions should be taken where 3(a), (b) and (c)) and listed in Table 2 should have problems are most likely to occur. Radiological provision for future subfloor extraction, ie surveys of existing houses have been undertaken to secondary measures (radon sump and extract pipe establish the extent of the problem. From these or ventilated subt1oor void, see section on surveys it is considered that precautionary measures secondary protection). should be taken as follows. 3 Within the areas listed in Tables 1 and 2, any site on which there is little or no possibility of an enhanced 1 New dwellings in Cornwall, Devon, Somerset, level of radon will obviously need no precautionary Northamptonshire and Derbyshire within the measures; for instance the subsoil may be such as to dark-shaded areas on the accompanying maps prevent the passage of radon or may be (Figures 3(a), (b) and (c)) and listed in Table 1 permanently saturated. should incorporate full radon precautions, ie both primary (radon-proof barrier, see section on These areas will need to be revised as more primary protection) and secondary measures information becomes available. This report will be (radon sump and extract pipe or ventilated amemleu acwruingly. The local aulhurily fur Lhe subfloor void, see section on secondary district in which you are proposing to build will be able protection). to confirm whether the Department of the Environment has amended the defined areas. Table 1 Areas where full radon precautions are required for new dwellings Districts and Boroughs Parishes and Towns Cornwall Caradon Boconnoc Liskeard St Keyne Broadoak Looe St Martin Callington Menheniot St Mellion Calstock Morval St Neot Dobwalls and Trewidland Pelynt St Pinnock Duloe Pillaton St Veep Landrake with St Emey Quethiock St Winnow Lanreath St Cleer Sheviock Lansallos St Dominick South Hill Lanteglos St Germans Warleggan Linkinhorne St Ive Carrick All Kerrier Breage Gweek Portreath Budock Helston Redruth Camborne Illogan St Anthony in Meneage Carharrack Lanner St Day Cam Brea Mabe St Gluvias Constantine Manaccan St Martin in Meneage Crow an Mawgan in Meneage Stithians Cury Mawnan Sithney Germoe Porthleven Wendron Gunwalloe (continued) 2 Table 1 (continued) Districts and Boroughs Parishes and Towns Cornwall (continued) North Cornwall Altamun Lawhitton Rural St Teath Advent Lesnewth St Thomas the Apostle Rural Blisland Lewannick St Tudy Bodmin Lezant South Petherwin Camelford Michaelstow Stokeclimsland Cardinham North Hill Tintagel Davidstow St Breock Tremaine Egloshayle St Breward Treneglos Egloskerry St Clether Tresmeer Forrabury and Minster St Endellion Trevalga Helland St Kew Trew en Laneast St Mabyn Wadebridge Lanhydrock St Minver Highlands Werrington Lani vet St Stephens by Launceston Rural Withiel Launceston Pen with All Restonnal All Devon Mid Devon Bampton More bath Oakford North Devon Arlington Countisbury Loxhore Bittadon East Down Lynton and Lynmouth Bratton Fleming Kentisbury West Down Brendon South Hams Aveton Gifford Holbeton Slapton Bigbury Holne South Brent Blackawton lvybridge South Huish Buckland-tout-Saints Kingsbridge South Milton Churchstow Kingston Sparkwell Comwood Kingsw ear Stoke Fleming Dartmouth Loddiswell Strete Dean Prior Modbury Thurlestone Diptford Newton and Noss Ugborough Dittisham North Huish West Alvington East Allington Rattery West Buckfastleigh Ennington Ringmore Woodleigh Halwell Shaugh Prior Yealmpton Harford Teignbridge Ashburton Buckland-in-the-moor Lustleigh Bickington Chris tow Manaton Bovey Tracy Dunsford Moretonhampstead Bridford Hennock North Bovey Buckfastleigh Ilsington Widecombe-in-the-moor Torbay Brixham Churston West Devon Bel stone Kelly Sheepstore Bere Ferrers Lamerton Sourton Brads tone Lewtrenchard South Tawton Bren tor Lifton Spreyton Bridestowe Lydford Sticklepath Buckland Monachorum Mary Tavy Stow ford Chagford Mary stow Sydenham Damerel Coryton Meavy Tavistock Dartmoor Forest Milton Abbot Thrushelton Drewsteignton Okehampton Tnrowleigh Dunterton Okehampton Hamlets Walkhampton Gidleigh Peter Tavy Whitchurch Guiw orthy Sampford Courtenay Horrabridge Sampford Spiney (continued) 3 Table 1 (continued) rnstricts and Borough� Parishes and Towns Somerset Mendip Cranmore Doulting Evercreech West Somerset Skilgate Upton Northamptonshire Kettering Broughton Grafton Underwood Pytchley Burton Latimer Kettering Thorpe Malsor Cranford Loddington Warkton Cranslcy Orton Weekley Wellingborough Finedon Isham Orlingbury Ureat Harrowden Little ttarrowden :Sywell Hardwick Mears Ashby Daventry Boughton Harles tone Overs tone Brix worth Holcot Pitsford Chapel Brampton Lamport Scaldwell Church Brampton Moulton Spratton Hanning ton Old Walgrave Northampton All Derbyshire Derbyshire Dales Abney and Abney Urange Great Hucklow