Radiation Protection Dosimetry Advance Access published April 9, 2014 Radiation Protection Dosimetry (2014), pp. 1–4
doi:10.1093/rpd/ncu110
INDOOR RADON PROBLEM IN ENERGY EFFICIENT MULTI-STOREY BUILDINGS I. V. Yarmoshenko1,*, A. V. Vasilyev1, A. D. Onishchenko1, S. M. Kiselev2 and M. V. Zhukovsky1 1 Institute of Industrial Ecology UB RAS, Sophy Kovalevskoy st., 20, Ekaterinburg 620990, Russia 2 Burnasyan Federal Medical Biophysical Center, Moscow, Russia *Corresponding author: [email protected]
INTRODUCTION The problems of energy saving and energy efficiency are in the spotlight of society. Buildings account for a considerable amount of the total energy consumption in developed countries. For northern countries with cold winters, heat saving is a significant problem during exploitation of the buildings. Few approaches for designing energy-efficient buildings were suggested in last decades. Effective insulation and low permeability can be achieved by the architectural solutions and building construction technologies as follow: † † † † † †
monolithic reinforced concrete structures; exterior insulation system; glazed loggias; high-performance window system; multiple glazing; special requirements for layout of the apartment.
Besides effective reduction in air permeability of building envelope, the application of such technologies results in decreasing air exchange rate and increasing radon accumulation in indoor air. In Russia, requirements on energy-efficient building construction were issued by governmental bodies since 1995. In course of time, utilisation of technologies mentioned above became prevailing, especially in multi-storey building construction. In this study, the problem of indoor radon was examined in existing energy-efficient multi-storey buildings in Ekaterinburg, Russia. MATERIALS AND METHODS The sample of residential buildings for analyses includes the multi-storey buildings that had constructed
after 2000. Every building possesses features of energysaving construction. Measurements of indoor radon concentrations were carried out by radon monitor AlphaGUARD installed in a living room. Radon monitor provides continuous measurements with registration of 1 h average value. Dwellers were instructed to keep their habits during all periods of measurements which lasted at least 6 months. The beginning of the measurements was assigned on either winter or summer, so the period of measurements covered both cold and warm seasons. Besides the radon concentration, the indoor temperature was also registered. The outdoor temperature necessary for the estimation of the dependence of radon level on indoor/ outdoor temperature differences was taken from publicly available official meteorological resources. Analysis of obtained radon concentration time series included estimation of radon entry rates, air exchange rates, contribution of diffusive and convective entry rates and effective concentration of 226Ra in building materials. The approach to analysis of indoor radon monitoring data was published early(1). As a rule, two typical modes of the room state are considered: (1) inactive ( people leave the room for long time or go to bed) and (2) active (with dwellers activity). As shown in Figure 1 within the time series of indoor radon concentration, two intervals related to inactive (T1 , t , T2) and active (t . T2) regimes of room using can be distinguished. The dependence of radon concentration on time A(t) under inactive condition and constant air exchange rate (AER) is described by the following non-linear equation: AðtÞ ¼ Amax ð1 elt Þ þ A0 elt þ Aatm
# The Author 2014. Published by Oxford University Press. All rights reserved. For Permissions, please email: [email protected]
ð1Þ
Downloaded from http://rpd.oxfordjournals.org/ at National Chung Hsing University Library on April 11, 2014
Modern energy-efficient architectural solutions and building construction technologies such as monolithic concrete structures in combination with effective insulation reduce air permeability of building envelope. As a result, air exchange rate is significantly reduced and conditions for increased radon accumulation in indoor air are created. Based on radon survey in Ekaterinburg, Russia, remarkable increase in indoor radon concentration level in energy-efficient multi-storey buildings was found in comparison with similar buildings constructed before the-energy-saving era. To investigate the problem of indoor radon in energyefficient multi-storey buildings, the measurements of radon concentration have been performed in seven modern buildings using radon monitoring method. Values of air exchange rate and other parameters of indoor climate in energy-efficient buildings have been estimated.
I.V. YARMOSHENKO ET AL.
¼ 2400 kg m23; L is the diffusion length in concrete, equal to (De/lRn)1/2; De is effective diffusion coefficient, De ¼ 2` 1026 m2 s21. RESULTS
1. Typical form of radon accumulation curve.
concentration
where A0 is radon concentration at t ¼ T1, Aatm ¼10 Bq m3 is radon concentration in outdoor air, Amax is the maximum radon concentration, which can be achieved under the given conditions, l is AER, h21. Assessment of AER and maximum radon concentration Amax in the buildings have been obtained using the method of determining parameters of radon entry in buildings(1). Using the values of Amax and l, radon entry rate, C, can be determined by the following equation: C ¼ Amax l
ð2Þ
The dependence of radon entry rate on temperature difference between indoor and outdoor atmosphere, DT, allows estimating the relationship between diffusion and convection mechanisms of indoor radon entry. The value of C(DT ¼ 0) is accepted as the diffusion entry rate. The value of AER under active mode of room exploitation is determined from the following equation: Amin ¼
C þ Aatm ; l
Table 1. Building characteristics and measurement periods. Room ID
Year of Floor construction
Number of floors
1
2003
7
16
2
2002
4
16
3
2007
3
24
4
2010
6
10
5
2012
3
16
6
2007
17
25
7
2012
13
16
Measurement period 22 June 2011– 26 Dec. 2011 28 Feb. 2009– 28 April 2009 01 July 2011– 22 Dec. 2011 24 Jan. 2012– 14 Aug. 2012 11 Jan. 2013– 01 Aug. 2013 27 June 2010– 28 Jan. 2011 21 Jan. 2013– 24 July 2013
ð3Þ
where Amin is radon concentration, achieved in the active mode of room using (Fig. 1). To assess the concentration of radium in building materials, the model urban building was designed using known room geometries and characteristics of building materials. The following expression relates the effective concentration of radium in model room, ARa, to the estimated radon entry rate and model room characteristics: ARa ¼
CðDT ¼ 0Þ V /S ; ARa lRn f r L tanhðd=LÞ
ð4Þ
where S is the surface areas of the model room; V is the volume of the model room, V/S ¼ 0.57 m; lRn is the decay constant of 222Rn; f is the emanation fraction for material, f ¼ 0.22; r is the material density, r
Figure 2. Mean, 95th percentile and 5th percentile indoor radon concentrations for studied rooms.
Page 2 of 4
Downloaded from http://rpd.oxfordjournals.org/ at National Chung Hsing University Library on April 11, 2014
Figure
In the period from 2009 to 2013, indoor radon measurements have been performed in seven rooms in different residential buildings. General characteristics of studied rooms are presented in Table 1. The apartments are located on the floors 3–17 in buildings with flours 16–25. The buildings were constructed in 2002– 2012. Mean, 95th percentile and 5th percentile indoor radon concentrations are presented in Figure 2. Mean indoor radon concentrations are in the range 48 –203 Bq m23. As can be seen from Figure 2 there is a high
INDOOR RADON PROBLEM IN ENERGY EFFICIENT MULTI-STOREY BUILDINGS
Table 2. Characteristic parameters of the radon entry and accumulation for studied rooms. Parameter
Mean
Range
Rn concentration, Bq/m23 AER Mode 1, h21 AER Mode 2, h21 Rn entry rate Bq (m3 h)21 Contribution of diffusion 226 Ra effective concentration, Bq kg21
133 0.20 0.55 38 76 % 40
48– 203 0.1– 0.26 0.39– 0.95 18– 62 51– 100 % 15– 53
Figure 3. Typical histogram of air exchange rate values.
Figure 4. Dependence of radon entry rate on temperature difference (diamonds, room 5; squares, room 7).
in other rooms. A considerable difference in the ventilation rate between active and inactive conditions of room operation can be seen, the modes of AER are 0.35 and 0.15, respectively.
DISCUSSION Early in 2000–2010 the representative radon survey in Ekaterinburg was conducted; the sample of the survey consisted of 404 apartments(2). According to the results of the survey the arithmetic mean of the radon concentration was 42 Bq m23. The lowest average radon concentration 35 Bq m23 was observed in the dwellings in the upper floors of buildings constructed between the 1970s and 1980s, and 90 % of the dwellings in this group did not exceed the level 70 Bq m23. Relatively high level of radon concentration in apartments on the upper floors of buildings, built in 1990, was found with an arithmetic mean of 65 Bq m23. In the current analysis of radon exposure in the seven energy-efficient buildings, higher indoor radon concentrations were found. The minimal room average value exceeds the city average level. The mean radon concentration in the group (133 Bq m23) exceeds the city average radon concentration by a factor of 3. In comparison with the multi-storey buildings constructed before the-energy-saving era, the rise of indoor radon concentration is even more remarkable (4-fold difference). The analysis of indoor radon concentration time series provides essential data to understand increased indoor radon concentration in the buildings where effective measures on heat saving were implemented. As can be seen in Table 2 and demonstrated in Figure 4, diffusion mechanism of indoor radon entry is prevailing in studied buildings. In half of rooms, especially on the upper floors, the diffusion contributes more than 34 of indoor radon and in some buildings up to 100 %.
Page 3 of 4
Downloaded from http://rpd.oxfordjournals.org/ at National Chung Hsing University Library on April 11, 2014
variability in 1-h values of indoor radon concentrations. In three rooms, the ratio of 95th percentile to 5th percentile exceeds 10 and only in one room it is ,4. In each house, the minimal registered radon concentration drops below the minimal detection level and maximum value amounts .100 Bq m3. Characteristics influencing radon entry estimated using the approach presented in Figure 1 and in equations (1), (2), (3) and (4) are shown in Table 2. The difference between AER at two modes of room state (inactive and active) is significant. Analysis of the contribution of diffusion and convective entry rates are presented in Figure 4, where dependence of total entry rate on temperature difference for rooms 5 and 7 are shown. In the room 5 located on the 3rd floor (2nd floor in English classification) minimal diffusion entry rate was found (51 % at DT ¼ 208C). The room number 7 located on 13th floor demonstrates the case of high diffusion contribution to radon concentration (.75 %). The dependence of C(DT ) is obvious in the room 5 and is minor in the room 7. The estimated effective concentrations of 226Ra in building materials are , 53 Bq kg. The samples of building materials were obtained directly from the construction corporation which constructs the significant part of new buildings in Ekaterinburg after 2000. The specific activity of 226 Ra, 232Th and 40K in the samples of building materials (monolithic and aerated concrete) was measured by scintillation gamma spectrometer. Figure 3 shows the histogram of values of AER in the room 6 which is typical and represents the pattern
I.V. YARMOSHENKO ET AL.
CONCLUSIONS (1) Indoor radon concentrations above the city average level are found in each of the studied apartments of buildings constructed with application of energy-efficient heat saving technologies.
(2) Diffusion mechanism of indoor radon entry in studied room prevails over convective one. (3) High indoor radon concentration and high contribution of diffusion radon entry in that type of building are caused by low permeability of building envelope and low indoor AER. (4) Content of 226Ra in building materials is not considered as main factor of radon entry. At the same time reduction in 226Ra concentration may be considered as counter radon measure in new buildings. (5) In course of time the higher indoor radon concentration in modern energy-efficient buildings in comparison with early constructed high permeable buildings will raise the average exposure of city population. Such situation contradicts the principle of optimization of radiation protection. FUNDING The study was supported by RFBR, research project No. 14-08-0677 a.
REFERENCES 1. Vasilyev, A. V. and Zhukovsky, M. V. Determination of mechanisms and parameters which affect radon entry into a room. J. Environ. Radioact. 124, 185– 190 (2013). 2. Yarmoshenko, I., Onishchenko, A. and Zhukovsky, M. Establishing regional reference indoor radon level on the base of radon survey data. J. Radiol. Prot. 33, 329–338 (2013).
Page 4 of 4
Downloaded from http://rpd.oxfordjournals.org/ at National Chung Hsing University Library on April 11, 2014
Importance of diffusion entry in energy-efficient buildings may be associated with reduced air permeability and lower AER. According to the evaluations in seven rooms, the AER values drastically depend on the mode of room using. Under conditions of inactive mode of room state, the AER are ,0.26 with average 0.20. Such AER is below the commonly accepted the lowest value 0.35 for dwellings. In the case of active mode of room state, when the most ventilation routes are open, the AER becomes higher, average AER ¼ 0.55. It is considered that the characteristic AER are commonly was .0.5 in the buildings constructed before setting the energy-efficient requirements. Presented estimation allows consideration of 226Ra content in building materials as a factor of high radon diffusive entry. As presented in Table 2 assessment of effective 226Ra concentration in building materials in seven buildings is 40 Bq kg21 in average and does not exceed 53 Bq kg21. Radioactivity of building materials is under official radiation control in Russia since 1989. The concentration of 226Ra about 50 Bq kg21 is typical for mineral rocks and sands used in building construction in the region. So, the content of 226Ra does not cause the elevation of radon concentration in energy-efficient buildings in comparison with that constructed earlier.
doi:10.1093/rpd/ncu110
INDOOR RADON PROBLEM IN ENERGY EFFICIENT MULTI-STOREY BUILDINGS I. V. Yarmoshenko1,*, A. V. Vasilyev1, A. D. Onishchenko1, S. M. Kiselev2 and M. V. Zhukovsky1 1 Institute of Industrial Ecology UB RAS, Sophy Kovalevskoy st., 20, Ekaterinburg 620990, Russia 2 Burnasyan Federal Medical Biophysical Center, Moscow, Russia *Corresponding author: [email protected]
INTRODUCTION The problems of energy saving and energy efficiency are in the spotlight of society. Buildings account for a considerable amount of the total energy consumption in developed countries. For northern countries with cold winters, heat saving is a significant problem during exploitation of the buildings. Few approaches for designing energy-efficient buildings were suggested in last decades. Effective insulation and low permeability can be achieved by the architectural solutions and building construction technologies as follow: † † † † † †
monolithic reinforced concrete structures; exterior insulation system; glazed loggias; high-performance window system; multiple glazing; special requirements for layout of the apartment.
Besides effective reduction in air permeability of building envelope, the application of such technologies results in decreasing air exchange rate and increasing radon accumulation in indoor air. In Russia, requirements on energy-efficient building construction were issued by governmental bodies since 1995. In course of time, utilisation of technologies mentioned above became prevailing, especially in multi-storey building construction. In this study, the problem of indoor radon was examined in existing energy-efficient multi-storey buildings in Ekaterinburg, Russia. MATERIALS AND METHODS The sample of residential buildings for analyses includes the multi-storey buildings that had constructed
after 2000. Every building possesses features of energysaving construction. Measurements of indoor radon concentrations were carried out by radon monitor AlphaGUARD installed in a living room. Radon monitor provides continuous measurements with registration of 1 h average value. Dwellers were instructed to keep their habits during all periods of measurements which lasted at least 6 months. The beginning of the measurements was assigned on either winter or summer, so the period of measurements covered both cold and warm seasons. Besides the radon concentration, the indoor temperature was also registered. The outdoor temperature necessary for the estimation of the dependence of radon level on indoor/ outdoor temperature differences was taken from publicly available official meteorological resources. Analysis of obtained radon concentration time series included estimation of radon entry rates, air exchange rates, contribution of diffusive and convective entry rates and effective concentration of 226Ra in building materials. The approach to analysis of indoor radon monitoring data was published early(1). As a rule, two typical modes of the room state are considered: (1) inactive ( people leave the room for long time or go to bed) and (2) active (with dwellers activity). As shown in Figure 1 within the time series of indoor radon concentration, two intervals related to inactive (T1 , t , T2) and active (t . T2) regimes of room using can be distinguished. The dependence of radon concentration on time A(t) under inactive condition and constant air exchange rate (AER) is described by the following non-linear equation: AðtÞ ¼ Amax ð1 elt Þ þ A0 elt þ Aatm
# The Author 2014. Published by Oxford University Press. All rights reserved. For Permissions, please email: [email protected]
ð1Þ
Downloaded from http://rpd.oxfordjournals.org/ at National Chung Hsing University Library on April 11, 2014
Modern energy-efficient architectural solutions and building construction technologies such as monolithic concrete structures in combination with effective insulation reduce air permeability of building envelope. As a result, air exchange rate is significantly reduced and conditions for increased radon accumulation in indoor air are created. Based on radon survey in Ekaterinburg, Russia, remarkable increase in indoor radon concentration level in energy-efficient multi-storey buildings was found in comparison with similar buildings constructed before the-energy-saving era. To investigate the problem of indoor radon in energyefficient multi-storey buildings, the measurements of radon concentration have been performed in seven modern buildings using radon monitoring method. Values of air exchange rate and other parameters of indoor climate in energy-efficient buildings have been estimated.
I.V. YARMOSHENKO ET AL.
¼ 2400 kg m23; L is the diffusion length in concrete, equal to (De/lRn)1/2; De is effective diffusion coefficient, De ¼ 2` 1026 m2 s21. RESULTS
1. Typical form of radon accumulation curve.
concentration
where A0 is radon concentration at t ¼ T1, Aatm ¼10 Bq m3 is radon concentration in outdoor air, Amax is the maximum radon concentration, which can be achieved under the given conditions, l is AER, h21. Assessment of AER and maximum radon concentration Amax in the buildings have been obtained using the method of determining parameters of radon entry in buildings(1). Using the values of Amax and l, radon entry rate, C, can be determined by the following equation: C ¼ Amax l
ð2Þ
The dependence of radon entry rate on temperature difference between indoor and outdoor atmosphere, DT, allows estimating the relationship between diffusion and convection mechanisms of indoor radon entry. The value of C(DT ¼ 0) is accepted as the diffusion entry rate. The value of AER under active mode of room exploitation is determined from the following equation: Amin ¼
C þ Aatm ; l
Table 1. Building characteristics and measurement periods. Room ID
Year of Floor construction
Number of floors
1
2003
7
16
2
2002
4
16
3
2007
3
24
4
2010
6
10
5
2012
3
16
6
2007
17
25
7
2012
13
16
Measurement period 22 June 2011– 26 Dec. 2011 28 Feb. 2009– 28 April 2009 01 July 2011– 22 Dec. 2011 24 Jan. 2012– 14 Aug. 2012 11 Jan. 2013– 01 Aug. 2013 27 June 2010– 28 Jan. 2011 21 Jan. 2013– 24 July 2013
ð3Þ
where Amin is radon concentration, achieved in the active mode of room using (Fig. 1). To assess the concentration of radium in building materials, the model urban building was designed using known room geometries and characteristics of building materials. The following expression relates the effective concentration of radium in model room, ARa, to the estimated radon entry rate and model room characteristics: ARa ¼
CðDT ¼ 0Þ V /S ; ARa lRn f r L tanhðd=LÞ
ð4Þ
where S is the surface areas of the model room; V is the volume of the model room, V/S ¼ 0.57 m; lRn is the decay constant of 222Rn; f is the emanation fraction for material, f ¼ 0.22; r is the material density, r
Figure 2. Mean, 95th percentile and 5th percentile indoor radon concentrations for studied rooms.
Page 2 of 4
Downloaded from http://rpd.oxfordjournals.org/ at National Chung Hsing University Library on April 11, 2014
Figure
In the period from 2009 to 2013, indoor radon measurements have been performed in seven rooms in different residential buildings. General characteristics of studied rooms are presented in Table 1. The apartments are located on the floors 3–17 in buildings with flours 16–25. The buildings were constructed in 2002– 2012. Mean, 95th percentile and 5th percentile indoor radon concentrations are presented in Figure 2. Mean indoor radon concentrations are in the range 48 –203 Bq m23. As can be seen from Figure 2 there is a high
INDOOR RADON PROBLEM IN ENERGY EFFICIENT MULTI-STOREY BUILDINGS
Table 2. Characteristic parameters of the radon entry and accumulation for studied rooms. Parameter
Mean
Range
Rn concentration, Bq/m23 AER Mode 1, h21 AER Mode 2, h21 Rn entry rate Bq (m3 h)21 Contribution of diffusion 226 Ra effective concentration, Bq kg21
133 0.20 0.55 38 76 % 40
48– 203 0.1– 0.26 0.39– 0.95 18– 62 51– 100 % 15– 53
Figure 3. Typical histogram of air exchange rate values.
Figure 4. Dependence of radon entry rate on temperature difference (diamonds, room 5; squares, room 7).
in other rooms. A considerable difference in the ventilation rate between active and inactive conditions of room operation can be seen, the modes of AER are 0.35 and 0.15, respectively.
DISCUSSION Early in 2000–2010 the representative radon survey in Ekaterinburg was conducted; the sample of the survey consisted of 404 apartments(2). According to the results of the survey the arithmetic mean of the radon concentration was 42 Bq m23. The lowest average radon concentration 35 Bq m23 was observed in the dwellings in the upper floors of buildings constructed between the 1970s and 1980s, and 90 % of the dwellings in this group did not exceed the level 70 Bq m23. Relatively high level of radon concentration in apartments on the upper floors of buildings, built in 1990, was found with an arithmetic mean of 65 Bq m23. In the current analysis of radon exposure in the seven energy-efficient buildings, higher indoor radon concentrations were found. The minimal room average value exceeds the city average level. The mean radon concentration in the group (133 Bq m23) exceeds the city average radon concentration by a factor of 3. In comparison with the multi-storey buildings constructed before the-energy-saving era, the rise of indoor radon concentration is even more remarkable (4-fold difference). The analysis of indoor radon concentration time series provides essential data to understand increased indoor radon concentration in the buildings where effective measures on heat saving were implemented. As can be seen in Table 2 and demonstrated in Figure 4, diffusion mechanism of indoor radon entry is prevailing in studied buildings. In half of rooms, especially on the upper floors, the diffusion contributes more than 34 of indoor radon and in some buildings up to 100 %.
Page 3 of 4
Downloaded from http://rpd.oxfordjournals.org/ at National Chung Hsing University Library on April 11, 2014
variability in 1-h values of indoor radon concentrations. In three rooms, the ratio of 95th percentile to 5th percentile exceeds 10 and only in one room it is ,4. In each house, the minimal registered radon concentration drops below the minimal detection level and maximum value amounts .100 Bq m3. Characteristics influencing radon entry estimated using the approach presented in Figure 1 and in equations (1), (2), (3) and (4) are shown in Table 2. The difference between AER at two modes of room state (inactive and active) is significant. Analysis of the contribution of diffusion and convective entry rates are presented in Figure 4, where dependence of total entry rate on temperature difference for rooms 5 and 7 are shown. In the room 5 located on the 3rd floor (2nd floor in English classification) minimal diffusion entry rate was found (51 % at DT ¼ 208C). The room number 7 located on 13th floor demonstrates the case of high diffusion contribution to radon concentration (.75 %). The dependence of C(DT ) is obvious in the room 5 and is minor in the room 7. The estimated effective concentrations of 226Ra in building materials are , 53 Bq kg. The samples of building materials were obtained directly from the construction corporation which constructs the significant part of new buildings in Ekaterinburg after 2000. The specific activity of 226 Ra, 232Th and 40K in the samples of building materials (monolithic and aerated concrete) was measured by scintillation gamma spectrometer. Figure 3 shows the histogram of values of AER in the room 6 which is typical and represents the pattern
I.V. YARMOSHENKO ET AL.
CONCLUSIONS (1) Indoor radon concentrations above the city average level are found in each of the studied apartments of buildings constructed with application of energy-efficient heat saving technologies.
(2) Diffusion mechanism of indoor radon entry in studied room prevails over convective one. (3) High indoor radon concentration and high contribution of diffusion radon entry in that type of building are caused by low permeability of building envelope and low indoor AER. (4) Content of 226Ra in building materials is not considered as main factor of radon entry. At the same time reduction in 226Ra concentration may be considered as counter radon measure in new buildings. (5) In course of time the higher indoor radon concentration in modern energy-efficient buildings in comparison with early constructed high permeable buildings will raise the average exposure of city population. Such situation contradicts the principle of optimization of radiation protection. FUNDING The study was supported by RFBR, research project No. 14-08-0677 a.
REFERENCES 1. Vasilyev, A. V. and Zhukovsky, M. V. Determination of mechanisms and parameters which affect radon entry into a room. J. Environ. Radioact. 124, 185– 190 (2013). 2. Yarmoshenko, I., Onishchenko, A. and Zhukovsky, M. Establishing regional reference indoor radon level on the base of radon survey data. J. Radiol. Prot. 33, 329–338 (2013).
Page 4 of 4
Downloaded from http://rpd.oxfordjournals.org/ at National Chung Hsing University Library on April 11, 2014
Importance of diffusion entry in energy-efficient buildings may be associated with reduced air permeability and lower AER. According to the evaluations in seven rooms, the AER values drastically depend on the mode of room using. Under conditions of inactive mode of room state, the AER are ,0.26 with average 0.20. Such AER is below the commonly accepted the lowest value 0.35 for dwellings. In the case of active mode of room state, when the most ventilation routes are open, the AER becomes higher, average AER ¼ 0.55. It is considered that the characteristic AER are commonly was .0.5 in the buildings constructed before setting the energy-efficient requirements. Presented estimation allows consideration of 226Ra content in building materials as a factor of high radon diffusive entry. As presented in Table 2 assessment of effective 226Ra concentration in building materials in seven buildings is 40 Bq kg21 in average and does not exceed 53 Bq kg21. Radioactivity of building materials is under official radiation control in Russia since 1989. The concentration of 226Ra about 50 Bq kg21 is typical for mineral rocks and sands used in building construction in the region. So, the content of 226Ra does not cause the elevation of radon concentration in energy-efficient buildings in comparison with that constructed earlier.
