Radon Control In New Homes: A Meta-Analysis of 25 Years of Research

Transcription

1 Radon Control In New Homes: A Meta-Analysis of 25 Years of Research William J. Angell Professor and Director Midwest Universities Radon Consortium University of Minnesota 2012 University of Minnesota 1

2 Overview Major Sections of this Paper Introduction Importance of Radon Control in New Residential Construction Persistent Issues and Limitations with Assessing New House Radon Control Techniques Guidance Documents, Standards, and Building Codes Methods Discussion of Results Overview of the Literature Size, Nature and Representativeness of Studies Passive Soil Depressurization Cap-on/Cap-off Studies Passive versus Active Soil Depressurization New House Radon Control Installation Issues Pressure Differential Measurements Radon Testing and Quality Assurance/Quality Control Evidence-Based Assessment of New Constr. Rn Control Research Conclusions 2012 University of Minnesota 2

3 Overview Motivation for this Paper My role as Chair of the World Health Organization s International Radon Project s Prevention and Mitigation Working Group Observed different opinions an approach to radon control in new houses The lack of a comprehensive review of the scientific, peerreviewed research My role as a building code advocate for radon control in new houses and interest in trade-offs between different approaches, for example: To what, if any, degree are subslab membranes critical What are the cost-effectiveness trade-offs of passive versus active control techniques 2012 University of Minnesota 3

4 Overview Importance of Radon Control in New Houses As documented in a 2008 paper I authored, the U.S. has more housing units with elevated radon than anytime in our history The major reason for this problem was that in a typical year more new homes were built that had elevated than the number of existing homes that mitigated This situation is also true for the vast majority of the world It has been demonstrated that in many cases, a public sector emphasis on radon control in new housing was more cost-effective for population-based risk reduction than a testing/mitigate approach This does not say that testing and mitigation are unimportant; rather we need to do more on the new construction front 2012 University of Minnesota 4

5 Overview Persistent Issues and Limitations with Radon Control in New House Research 1. The significance of post-construction radon test results is open to question since there can be no preconstruction indoor radon measurements 2. Pre- and post- passive and active soil depressurization (PSD and ASD) research involves radon testing in different time periods 3. Assessing efficacy of specific or combinations of specific radon control techniques is not possible in the vast majority of studies 4. Most studies have used short-term radon measurements and it is unclear how representative these measurements are of annual averages 5. Most studies have involved small samples of houses in single communities and thus, it is unknown how representative the results may be of national averages or those in different regions 2012 University of Minnesota 5

6 Overview A Sample of U.S. Guidance Documents, Standards, and Code (1:2) U.S. EPA (1987) Radon Reduction in New Construction, An Interim Guide ASTM (1990) Emergency Standard Guide for Radon Control Options for the Design and Construction of New Low Rise Residential Buildings Clarkin and Brennan (1991) Radon-resistant Construction Techniques for New Residential Construction (EPA) U.S. EPA (1994) Model Standards and Techniques for Radon Control in New Residential Buildings Council of American Building Officials (1995) One and Two Family Dwelling Code U.S. EPA (1999) Design of a program to measure the effectiveness of passive radon-resistant new construction 2012 University of Minnesota 6

7 Overview A Sample of International Guidance Documents, Standards, and Code Clavensjö and Åkerblom (1994) The Radon Book: Measures against Radon Building Research Establishment (BRE) (1999a, 1999b) Construction of New Buildings on Gas-contaminated Land and Radon: Guidance on Protective Measures for New Dwellings Roserens, et al. (2000) Swiss Radon Handbook National Building Code of Finland (Ministry of the Environment, 2003) Arvela, et al. (2008) Radon prevention and mitigation in Finland: Guidance and practices in AARST Symposium Proceedings 2012 University of Minnesota 7

8 Overview Methods This analysis focused largely on North American research The literature search centered on peer-reviewed papers in scholarly journals and conference proceedings U.S. Environmental Protection Agency s (EPA) International Symposium on Radon and Radon Reduction Technology proceedings American Association of Radon Scientists and Technologists International Radon Symposium proceedings EPA research reports Health Physics, Journal of Air & Waste Management Association, and Radiation Protection Dosimetry National Association of Home Builders Research Center research reports 2012 University of Minnesota 8

9 Overview of Results The total number of documents reviewed was 57 As reflected the following slide, 36 papers of the more data rich publications are summarized by Author(s) and year of publication Number of houses and number of communities in the study Whether the houses were built according to EPA guidance or similar codes Radon testing details Whether pressure differential measurements were reported Types of radon control techniques used or assessed in the study Whether quality assurance and/or quality control were reported 2012 University of Minnesota 9

10 2012 University of Minnesota 10

11 Some Pivotal Papers Pivotal documents included: Murane (1988) describing data from 148 new houses in EPA s New House Evaluation program built by 5 builders in CO and MI EPA (1999) guidance document or protocol on measuring the effectiveness of PSD systems Weiffenbach and Marshall (2003) reported very extensive data logging in 8 houses Arvela, Holmgren and Reisbacka (2011) present the results from the first national survey of radon-control systems in 1561 new Finnish houses 2012 University of Minnesota 11

12 Radon Concentration by Foundation Type: Finland (Arvela, Holmgren and Reisbacka [2011]) Rn Concentration (Bq m -3 ) Foundation Type # Houses Average Median Slab-on-grade Monolithic Slab Crawlspace Semi-basement and Basement No Information Total These data are from a 2009 national random survey of Finnish houses built between 2004 and 2006 when new building code requirements were enacted The new code required a loop of subslab radon pipe, sealing of the cold joint using a strip of sealed bitumen felt, and a radon vent pipe discharge above the roof 2012 University of Minnesota 12

13 Effects of Passive Methods in Finnish Slabon-Grade Houses(Arvela, Holmgren and Reisbacka [2011]) Passive Preventive Measure None PSD Piping & Sealing PSD Piping & No Sealing Number of Houses Average Rn Concentration (Bq m -3 ) Median Rn Concentration (Bq m -3 ) House Rn Compared to Local Rn Concentrations 0% 57% 41% These data are from a 2009 national random survey of Finnish houses built between 2004 and 2006 when new building code requirements were enacted 2012 University of Minnesota 13

14 Winter and Summer Rn Concentration with Cap-on/Cap-off NAHB Houses Winter Summer Stack Closed 192 (5.2 pci/l) 133 (3.6 pci/l) Stack Open 93 (2.5 pci/l) 67 (1.8 pci/l) Percent Reduction 52% 50% The data in this table Reflects seasonal variation - stack effect in 22 houses with PSD systems in 6 states But the similarity in percentage of radon reduction is notable Should be interpreted with caution since many of the houses had deficiencies in radon-control techniques 2012 University of Minnesota 14

15 PSD Cap-on/Cap-off Studies The following table summarizes the findings of 12 studies of radon concentrations in 224 houses with PSD systems: Capped (nonfunctional) The average radon concentration was 231 Bq m -3 (6.2 pci/l) Open (functional) The average radon concentration was 127 Bq m -3 (3.4 pci/l)... a 55% average reduction in indoor radon concentrations 2012 University of Minnesota 15

16 PSD Cap-on/Cap-off Studies (Bq m -3 ) Study (alpha order) Number Houses Capon Cap -off % Notes Brehm, PSD compromised; 2 day Rn tests, location & season unspecified Dewey, 1994 Basement Basement Rn tests; 36 tested same season First Floor First floor Rn tests; 36 tested same season Average Fort Collins, Houses built 2005; Rn tests length & location unspecified Hagerty, PSD compromised; 5-7 day Rn tests, season & location unspecified Hanson, PSD compromised; January basement Rn tests; test length unspecified LaFollette, day Rn tests on the lowest level suitable for occupancy Najafi, of 14 houses with PSD tested NAHB, 1996 Winter PSD compromised; winter lowest level Rn tests; test length unspecified Summer Summer Rn tests in lowest level; test length unspecified Average Saum, Cap-off approximate value; winter Rn tests Snead, PSD compromised; average 7 day winter Rn tests; location unspecified Tyson, Main floor 48 hour Rn tests; testing season unspecified Weiffenbach, Basement, 6+ day, winter Rn tests Total 224 Overall Weighted Average % Reduction 2012 University of Minnesota 16

17 Winter and Summer Cap-on/Cap-off (NAHB, 1996) Winter Summer Stack Closed 192 (5.2 pci/l) 133 (3.6 pci/l) Stack Open 93 (2.5 pci/l) 67 (1.8 pci/l) Percent Reduction 52% 50% Study involved 22 houses in six states and is the only published study that looked at seasonal PSD performance These results should be interpreted with caution since many of the houses had deficiencies in radon-control techniques 2012 University of Minnesota 17

18 PSD versus ASD Radon Control in New Houses The following table summarizes the research findings of 9 studies on the comparative performance of PSD and ASD system in 61 houses Overall, ASD offers More than an 80% reduction in indoor radon concentrations in new houses Greater radon reduction than PSD 2012 University of Minnesota 18

19 PSD vs. ASD Performance Study No.of Houses Radon Tests (Bq m -3 ) PSD PSD Capped Open ASD Notes Brennan, Five day Rn tests, season & location unspecified Clarkin, April-May, 6 day basement Rn tests Dewey, Basement Rn tests Keränen, Two month, first floor Rn test, seasons varied Lewis, Location, season & length of Rn tests generally unspecified Najafi, Four first floor Rn tests, seasons & length of tests unspecified Saum, Location, season & length of Rn tests unspecified Tyson, Main floor 48 hour Rn tests; testing season unspecified Weiffenbach, PSD Rn with poor sealing; ASD with sealing Total 61 Weighted Averages PSD Capped to ASD % reduction PSD Open to ASD % reduction 2012 University of Minnesota 19

20 New Construction Radon Control Defects The following table summarizes defects noted in studies of radon control in new houses Since the assessments did not involve a common set of criteria, the absence of cited problems in any specific study does not mean the problem was not present Furthermore, many of the studies did not list the frequency of the problems, and thus one cannot conclude the relative frequency of the problems Only the Finnish study (Keränen, 2008) was a nationally representative study, and thus, the U.S. studies cannot be viewed as representative of all new homes built with radoncontrol techniques 2012 University of Minnesota 20

21 Radon Control Installation Issues Problem HVAC Duct Leaks Depressurize Soil Contacted Area HVAC Blower Depressurizes Soil Contacted Area Subslab Permeable Layer Missing or Incomplete Sealing Incomplete Sumps Unsealed Air Leaks Around PSD Stack Slab Penetration Excessive Floor Penetrations Above Crawl Space Subslab or Crawl Space Membrane Missing or Incomplete Untrapped Condensation Drains Through Slab Uncapped Concrete Block Foundation Walls Air Leaks to the Outdoors Isolated Subslab or Submembrane Areas Foundation or Slab Sealing without PSD No PSD Vent Stack Horizontal PSD Pipe Lacking Drainage Slope PSD Pipes Blocked by Construction Debris PSD Pipes Blocked by Soil PSD Stack Pipe too Small (<7.6 cm [<3"]) PSD Vent Routed Through Unheated Space PSD does not Discharge Above Roof PSD Pipe Joints Unsealed and Leaky PSD Discharge Lacks Bird Screen System Labels Lacking Radon Performance Tests not Done Murane, 1988 Saum, 1990 Saum, 1993 Dudney, 1992 Spears, 1993 Dewey, 1994 Fay, University of Minnesota 21 Tyson, 1995 NAHB, 1996 Lewis, 1999 Brehm, 2002 Hagerty, 2002 Snead, 2003 Hanson, 2005 Fort Collins, 2006 Keränen, 2008

22 Discussion Evidence-based Assessment: RCNH Research Scottish Intercollegiate Guidelines for ranking research: Ia evidence from meta-analysis of randomized controlled trials; Ib evidence from at least one randomized controlled trials; IIa evidence from a well-designed, controlled study without randomization; IIb evidence from at least one other type well designed, quasiexperimental study; III evidence from well designed, nonexperimental, descriptive studies such as comparative studies, correlation studies, and case studies; and IV evidence from expert committee reports or opinions and/or clinical experience of respected authorities University of Minnesota 22