Building materials generally contain a certain amount of naturally occurring radioactive substances. From a radiobiological point of view, the isotopes potassium-40 (K-40), radium-226 (Ra-226) and thorium-232 (Th-232) are of particular importance. With regard to the question of whether or not a particular material should be used as a building material from a radiobiological point of view, it is often recommended that only those building materials with a so-called assessment number B of less than 1 should be used. This evaluation number B is calculated as follows:

• B = K/4810 + R/370 + T/259
  

For K the activity of K-40, for R the activity of Ra-226 and for T the activity of Th-232 in the building material concerned in becquerels per kilogramme (Bq/kg) must be used; the unit Bq/kg must be omitted in each case.

Irrespective of this, care should be taken in the selection of building materials to ensure that their radioactivity content is as low as possible. In particular, no materials should be used whose Ra-226 activity exceeds 100 Bq/kg.

The following list summarises the results of a measurement campaign on natural radioactivity in building materials conducted by the Physical Environmental Analysis working group. The entries have the form:

• Building material designation / R / T / K / B (R, T, K each in Bq/kg)

• Floor tile COTTO IL FERRONE, red tone /R= 24 /D= 36 /K= 717 /W= 0.35
• Floor tile DA230 BAUXITE, grey clay, Flaviker s.p.a. /R= 60 /D= 68 /K= 333 /W= 0,49
• Floor tile POTZENBURG 100,clay grey, BRD /R= 44 /D= 49 /K= 660 /B= 0,45
• Floor tile POTZENBURG 100,tone black, BRD /R= 63 /D= 79 /K= 928 /B= 0,67
• Floor tile AETERNA TEBE CLASS, glaze grey/grey tone /R= 51 /D= 48 /K= 928 /B= 0,52
• Floor tile BUILDING BIANCO, glaze white/shade grey /R= 67 /D= 48 /K= 930 /W= 0,56
• Floor tile OREGON 5, glaze white/shade grey, Cer. Omega /R= 76 /D= 69 /K= 768 /W= 0,63
• Floor tile NEVE, glaze white/glaze white, Recer/Portugal /R= 132 /D= 42 /K= 1032 /W= 0,73
• Floor tile STOECKLER, glaze red-brown/shade grey, BRD /R= 76 /D= 71 /K= 1350 /B= 0,76
• Floor tile glaze brown/clay brown /R= 39 /D= 45 /K= 458 /B= 0,37
• Floor tile clay red-brown, Italy /R= 43 /D= 57 /K= 1051 /W= 0.55
• Tile, STOECKLER, glaze white/clay light brown, Germany /R= 80 /D= 68 /K= 1174 /W= 0.72
• Tile, FABRESA, glaze white matt/tone brown, Spain /R= 115 /D= 69 /K= 1196 /B= 0,83
• Tile, CERAMICHE GIRARDI, glaze white/tone brown /R= 47 /D= 22 /K= 680 /W= 0.35
• Tile, TOPAZIO GRIGIO, glaze white/tone brown /R= 47 /D= 38 /K= 1118 /W= 0,51
• Tile, BIANCO D'ITALIA, glaze white/tone brown /R= 55 /D= 36 /K= 947 /B= 0.48
• Tile, VILLEROY&BOCH JU87, glaze white/tone white /R= 63 /D= 58 /K= 353 /B= 0.47
• Tile, VILLEROY&BOCH JL20, glaze white/tone white /R= 67 /D= 54 /K= 340 /W= 0.46
• Tile, VILLEROY&BOCH JU47, glaze white/tone white /R= 71 /D= 55 /K= 400 /W= 0.49
• Tile, VILLEROY&BOCH J 869, glaze white/grey tone /R= 68 /D= 63 /K= 841 /B= 0.60
• Tile, VILLEROY&BOCH J 868, glaze white/grey tone /R= 80 /D= 69 /K= 863 /B= 0.66
• Tile, VILLEROY&BOCH FM 20, glaze white/grey tone /R= 86 /D= 77 /K= 752 /B= 0.69
• Tile, VILLEROY&BOCH J 958, glaze grey/grey tone /R= 115 /D= 70 /K= 980 /B= 0.78
• Tile, VILLEROY&BOCH J 959, glaze grey/grey tone /R= 175 /D= 71 /K= 907 /B= 0.94
• Tile, TEBE CLASSICO, glaze grey/grey tone /R= 78 /D= 62 /K= 986 /B= 0.66
• Tile, glaze beige/shade grey, Italy /R= 86 /D= 47 /K= 769 /B= 0.57
• Tile, glaze white, Italy /R= 73 /D= 41 /K= 919 /B= 0.55
• Tile, Italy, purchase: 2900 Oldenburg /R= 73 /D= 45 /K= 911 /B= 0,56
• Wall tile EXPORT CERAN, glaze white/clay white, Italy /R= 84 /D= 71 /K= 1163 /B= 0,74
• Wall tile L'ULTRA LEGGERO, glaze white/tone white /R= 66 /D= 62 /K= 1029 /W= 0,63
• Wall tile T010, glaze white/shade grey, Cer. faetano, RSM /R= 53 /D= 49 /K= 676 /W= 0,47
• Wall tile JASBA 1150, glaze white/shade grey, 5419 Oetzin /R= 72 /D= 53 /C= 811 /W= 0,57
• Wall tile SALZBURG 5, glaze white/tone brown, Cer. Omega /R= 35 /D= 24 /K= 706 /B= 0,33
• Wall tile VB 920, glaze grey/tone brown, Italy /R= 137 /D= 93 /K= 1111 /W= 0,96
• Wall tile SERVAIS, glaze brown/tone white, Germany /R= 62 /D= 86 /K= 390 /W= 0,58
• Wall tile glaze white/clay white, Argentina /R= 65 /D= 71 /K= 488 /B= 0,55
• Wall tile glaze white/clay white, FRG /R= 68 /D= 59 /K= 1043 /B= 0,63
• Wall tile glaze white/clay white, BRD /R= 68 /D= 65 /K= 367 /B= 0,51
• Wall tile glaze white/shade beige, Italy /R= 70 /D= 55 /K= 921 /B= 0,59
• Wall tile glaze white/tone white, Germany /R= 107 /D= 78 /K= 494 /B= 0,69
• Wall tile glaze white/red tone, Italy /R= 112 /D= 93 /K= 1214 /B= 0,91
• Wall tile glaze dark green/tone white, Germany /R= 57 /D= 39 /K= 140 /B= 0,33

• PENTER foundation brick, red clay /R= 40 /D= 51 /K= 615 /B= 0.43
• Clinker brick, red clay, 2864 Hambergen /R= 23 /D= 32 /K= 487 /B= 0.29
• Clinker brick, BOCKHORNER red clay, 2935 Bockhorn /R= 32 /D= 33 /K= 490 /B= 0.32
• Clinker KNABE, white clay, 2872 Kirchkimmen /R= 37 /D= 44 /K= 479 /B= 0.37
• Clinker KNABE, brown clay, 2872 Kirchkimmen /R= 26 /D= 32 /K= 564 /B= 0.31
• Clinker KNABE, red-brown clay, 2872 Hude-Kirchkimmen /R= 31 /D= 40 /K= 575 /B= 0.36
• Clinker brick WWK, red clay, 4240 Emmerich /R= 51 /D= 44 /K= 717 /B= 0.46
• Clinker brick, clay, 2900 Oldenburg /R= 52 /D= 33 /K= 565 /B= 0.39
• Pressed clinker ARGELITH, red clay, BRD /R= 41 /D= 63 /K= 916 /B= 0.54
• Brick, sand-lime brick /R= 6 /D= 5 /K= 151 /B= 0.07
• Brick, sand-lime brick, 2909 Boesel /R= 8 /D= 5 /K= 195 /B= 0.08
• Brick, sand-lime brick, 4597 Ahlhorn /R= 6 /D= 6 /K= 214 /B= 0.08
• Masonry block, WIENERBERGER, red clay /R= 35 /D= 37 /K= 775 /B= 0.40
• POROTON masonry block, Wienerberger, 2905 Jeddeloh /R= 46 /D= 44 /K= 583 /B= 0.42
• POROTON masonry block, Wienerberger, 2139 Sittensen /R= 81 /D= 49 /K= 619 /W= 0.54
• POROTON masonry block, 4460 Lingen /R= 42 /D= 54 /K= 1132 /B= 0.56
• POROTON masonry block, Egersund/Denmark /R= 31 /D= 33 /K= 552 /B= 0.33
• POROTON-ZIEGEL masonry block, Wienerberger /R= 32 /D= 38 /K= 628 /B= 0.36
• UNIPOR-ZIEGEL masonry block, 4904 Enger/Westphalia /R= 92 /D= 56 /K= 698 /B= 0.61
• Masonry brick, concrete, purchase: 2900 Oldenburg /R= 6 /D= 3 /K= 141 /B= 0.06
• Fireclay brick BURTON, 4520 Melle /R= 53 /D= 64 /K= 423 /B= 0.48
• Fireclay brick, 4460 Lingen /R= 50 /D= 76 /K= 758 /B= 0.59

• Expanded clay LECA, 2080 Pinneberg /R= 23 /D= 37 /K= 674 /B= 0.35
• Expanded clay, Liaporwerk, 7201 Tuningen /R= 34 /D= 40 /K= 581 /B= 0.37
• Roof tile WITTENBERG, red clay /R= 47 /D= 19 /K= 289 /B= 0.26
• Gypsum KNAUF HAFTPUTZGIPS /R= 43 /D= 28 /K= 58 /B= 0.24
• Gypsum aerated concrete plaster GOLD-WEISS-SPEZIAL, for interior use /R= 9 /D= 4 /K= 44 /B= 0.05
• Model plaster JWO, 4420 Coesfeld /R= 3 /D= 1 /K= 7 /B= 0.01
• Lime DYCKERHOFF HK 80, 4540 Lengerich /R= 5 /D= 11 /K= 150 /B= 0.09
• Limestone gravel from the Weserbergland /R= 7 /D= 22 /K= 12 /B= 0.11
• Gravel RHEINKIES, Strasbourg /R= 12 /D= 16 /K= 224 /B= 0.14
• Gravel WESERKIES, 3078 Stolzenau /R= 14 /D= 29 /K= 519 /B= 0.26
• Sand WESERSAND (screed sand), purchase: 2900 Oldenburg /R= 11 /D= 15 /K= 414 /B= 0.17
• Sand WESERSAND, 3078 Stolzenau /R= 7 /D= 7 /K= 288 /B= 0.11
• Sand ROEHRS, 3071 Leese /R= 8 /D= 8 /K= 249 /B= 0.10
• Trass flour TUBAG, 5473 Kruft /R= 57 /D= 85 /K= 1243 /B= 0.74
• Cement DYCKERHOFF PORTLAND-, 4540 Lengerich /R= 7 /D= 7 /K= 267 /B= 0.10
• Cement, purchase: 4048 Grevenbroich /R= 13 /D= 12 /K= 180 /B= 0.12