Different dwellings each of volume ranged from30 to 310 cubicmeterswere selected in different locations on the basis of quality of construction, age, similar nature ofwalls and floorings. Twin cup dosimeters consisting of LR- 115 plastic track detectors were installed in 42 houses to study the variation in indoor radon and thoron concentrations to record the significance of volume of the roomthat are similar type of constructions.After an exposure period of 90 days the films were removed and etched chemically in 10% NaOH solution at 60 ºC for an hour with mild agitation throughout, the etched films were alpha counted using spark counter. The measurement is continued for one complete calendar year to observe the seasonal variations. The large variations in the concentrations were observed during winter and summer seasons than in rainy and autumn seasons of the calendar year. The higher concentrations of radon, thoron and their progeny, and dose rates were observed in a roomof lower volume than in higher volume. The 222Rn and 220Rn concentrations in dwellings of volume 30 to 310 cubic meters ranged between 4Â93 Bq mÂ3 whereas their progeny concentrations ranged between 0.012Â2.45 mWL, respectively. It is observed that the enhancement of volume by almost ten-fold reduces the concentration of 222Rn to 23% and that of 220Rn to 13% of the studied locations provided all conditions remain unaltered. Further it is observed, if the volume of room varies as geometric progression, there is no dependence on the concentrations in the same ratio. The annual effective dose due to radon, thoron and their progenies ranged between 0.105 and 0.457mSvyÂ1 for the volume specified above.