The acoustical and thermal properties of materials have contradictory behaviour. Constructions, which provide good acoustic absorption usually, have a low thermal inertia and vice versa. It is therefore important to find a balance between acoustic absorption and thermal inertia in order to deliver well designed buildings. This paper presents an integrated solution, developed to assess the room acoustics performance of a building within the ESP-r environment. The approach used in this work applies the diffuse-sound field theory to calculate the reverberation time via three analytical equations: Sabine, Eyring and Millington approaches. The calculation includes the absorption of the space boundaries, the occupants and furniture. Also included is the air absorption, which takes into account the air temperature and humidity from the thermal simulation. Finally, a case study has been analysed. The simulation results have been compared with measurements from a monitored building to verify the validity of the approach.