United States Environmental Protection Agency National Risk Management Research Laboratory Research Triangle Park, NC 27711 Research and Development EPA/600/SR-95/114 August 1995 4>EPA Project Summary Evaluation of Building Design, Construction, and Performance for the Control of Radon in Florida Houses: Evaluation of Radon Resistant Construction Techniques in Eight New Houses D.E. Hintenlang, A. Shanker, FT. Najafi, and C.E. Roessler Eight houses were studied through- out their construction in North Central Florida. Each house was built in com- pliance with the proposed radon resis- tant construction standard being developed by the Florida Department of Community Affairs. Post-construc- tion monitoring was performed over a minimum 6-day period for each struc- ture during which each house was op- erated in three different heating, ventilation, and air-conditioning (HVAC) system configurations. Continuous measurements of indoor radon concen- trations, house ventilation rates, across- slab differential pressures, and interzone differential pressures pro- vided time resolved radon entry rates and a performance index for passive radon barriers. Radon entry rates were found to be relatively constant through- out the measurement periods and for different house operating conditions, implying that the passive radon barrier eliminates the majority of convective entry. The passive barriers maintained radon entry fluxes at less than 1.2 pCi rrr2 s~1 for sub-slab radon concentra- tions as high as 9,500 pCil1. The study results also demonstrate that the operation of well designed and constructed HVAC systems do not sig- nificantly affect indoor radon concen- trations, regardless of the pressures that may be induced between interior air zones. House ventilation rates should, however, be equal to or greater than 0.25 air change per hour in order to prevent the accumulation of elevated radon concentrations since passive barriers do not block 100% of the ra- don from entering. This Project Summary was developed by EPA's National Risk Management Research Laboratory, Research Triangle Park, NC, to announce key findings of the research project that is fully docu- mented in a separate report of the same title (see Project Report ordering infor- mation at back). The State of Florida has undertaken the development of radon resistant construc- tion standards for newly constructed build- ings in the state. This is a premier effort to develop a technically based building code for both residential and large/commercial buildings and focuses on the specific con- struction practices and environmental con- ditions found in this region of the country. ------- The work presented here consists of an evaluation of the effectiveness of the ra- don resistant construction standards for residential construction which will enter the rule-making process later this year Eight houses were studied throughout their construction in North Central Florida. Each house was built in compli- ance with the proposed radon resistant construction standard being developed by the Florida Department of Commu- nity Affairs. Post-construction monitor- ing was performed over a minimum 6-day period for each structure during which each house was operated in three different heating, ventilation, and air-con- ditioning (HVAC) system configurations. Continuous measurements of indoor ra- don concentrations, house ventilation rate, across-slab differential pressures, and interzone differential pressures pro- vided time resolved radon entry rates and a performance index for passive radon barriers. Each of the houses was built over high radon potential soils and was constructed implementing the ra- don resistant construction standards be- ing developed by the Florida Department of Community Affairs. Radon entry rates were calculated from the measured parameters. The resulting radon entry rates were relatively constant throughout the measurement periods and for different house operating conditions, with variations of indoor radon concentra- tions being driven predominantly by the house ventilation rate. Normal cycling in the barometric pressure produced a semi- diurnal cycle in the across-slab differential pressures in all of the houses studied. These differential pressures did not, how- ever, correlate with observed changes of the radon entry rate, indicating that pres- sure driven flow is not providing a major contribution to the radon entry. These re- sults imply that the passive radon barrier effectively reduces a large fraction of the convective driven entry. Similarly, aver- aged radon entry rates and entry fluxes were not correlated to the foundation slab cracking present in these structures. Al- though measures were taken to reduce the amount of slab cracking, half of the slabs studied exhibited some unplanned slab cracks. A general figure of merit, the entry rate per unit slab area, or radon entry flux is useful and suggests that residences built using the radon resistant construction stan- dard should be able to have entry fluxes less than about 1.2 pCi nr2 s~1. It does not appear that sub-slab radon concentrations were high enough to overcome the effec- tiveness of passive barriers reached in this study. The passive barriers have dem- onstrated their effectiveness at maintain- ing radon entry fluxes at less than approximately 1.2 pCi nr2 s~1 for sub-slab radon concentrations as high as 9,500 pCi M. If passive barrier techniques be- come ineffective at some concentration of sub-slab soil gas radon, it is probably greater than 10,000 pCi M. In fact, we observed excellent performance for House #11 at 9,500 pCi M, which had quite a low radon entry flux. This research provides support for and suggests some changes to the current version of the radon resis- tant construction standards in several ar- eas. Overall the study demonstrates that the implementation of passive barriers can be practically incorporated in foundations during new house construction and that, when implemented as prescribed by the standards, can successfully prevent in- door radon concentrations from exceed- ing the 148 Bq rrr3 guidelines in most houses. The study results also demonstrate that the operation of well designed and con- structed HVAC systems (i.e., those built to current building code standards) does not significantly affect indoor radon con- centrations, regardless of the pressures that may be induced between interior air zones. Therefore, there should be no re- quirement for the radon resistant construc- tion standards to include provisions to transfer air between different air zones within a structure such as transfer grills, and door undercuts. A more important sub- ject with which HVAC systems do interact is the overall house ventilation rate. It appears to be prudent to ensure an aver- age house ventilation rate equal to, or greater than, 0.25 air change per hour in order to prevent the accumulation of el- evated radon concentrations, since pas- sive barriers do not block 100% of the radon from entering. The radon resistant construction stan- dards developed for residential construc- tion by the Florida Department of Community Affairs have been demon- strated to be technically feasible and can be implemented on a practical basis. Pas- sive barrier techniques can provide houses constructed over sandy fills and high soil gas radon concentrations with acceptable indoor radon concentrations as long as house ventilation rates are not permitted to be too low, and active soil depressur- ization continues to be an inexpensive and very effective backup to passive bar- riers. ------- D.E. Hintenlang, A. Shanker, F.T. Najafi, andC.E. Roesslerare with the University of Florida, Gainesville, FL 32611. David C. Sanchez is the EPA Project Officer (see below). The complete report, entitled "Evaluation of Building Design, Construction, and Performance for the Control of Radon in Florida Houses: Evaluation of Radon Resistant Construction Techniques in Eight New Houses," (Order No. PB95- 253910; Cost: $27.00, subject to change) will be available only from National Technical Information Service 5285 Port Royal Road Springfield, VA22161 Telephone: 703-487-4650 The EPA Project Officer can be contacted at National Risk Management Research Laboratory (formerly Air and Energy Engineering Research Laboratory) U.S. Environmental Protection Agency Research Triangle Park, NC 27711 United States Environmental Protection Agency National Risk Management Research Laboratory (G-72) Cincinnati, OH 45268 BULK RATE POSTAGE & FEES PAID EPA PERMIT No. G-35 Official Business Penalty for Private Use $300 EPA/600/SR-95/114 ------- |