When fly ash is used in construction materials, it can increase exposure to gamma radiation and radon. This study aimed to evaluate the radioactive concentrations and exposure doses in concrete samples of grades M300 and M400 with added fly ash. We utilized an HPGe spectrometer and the RESRAD-BUILD simulation program for this purpose. The results indicated that the average activities of ²²⁶Ra and ²³²Th were below the reference values, while the average activity of ⁴⁰K exceeded the UNSCEAR limit. The findings for M300 and M400 were 1.5 and 1.6 times higher, respectively, than the global average for indoor absorbed gamma dose. However, the annual effective dose in residential and office spaces for both concrete grades remained below the 1.0 mSv y⁻¹ limit for the population. Multivariate analysis showed that radon and total dose were affected by the activities of ²²⁶Ra and ²³²Th, but not by ⁴⁰K. Additionally, the radon dose was impacted by the air exchange rate, with an increase in air circulation leading to a reduction in the radon dose. Overall, the results indicate that living and working in houses constructed with concrete samples of grades M300 and M400, mixed with fly ash content ranging from 0 % to 50 %, was safe for individuals.