Abstract High rise multiple dwelling houses with balconies have been frequently constructed in recent years because of the concentration of population in a big city. The wall surface of buildings with balconies and mullions, becomes extremely rough. To the present, wind loading on glass and cladding have been mainly derived from tests on buildings with smooth surfaces. However, effects of reduction of wind pressures are considerable for walls with surface roughnesses such as balconies. The paper describes the results of an experimental study carried out in a Gottingen-type wind tunnel under uniform flow and boundary layer flow over urban terrain. The basic model of study represented square buildings 75 m high and 25 m wide in a scale of 1/300. The surface roughness attached on all building walls was: uniform roughness of maximum size equal to 0.21 m in full scale, and three kinds of balconies of 0.63, 1.25 and 2.5 m wide without mullions, and 0.63 m wide balconies with mullions. The experimental data indicate that wind pressures were remarkably affected by the surface roughness, particularly near the leading edge of the side wall on which local severe peak pressures decrease with increasing roughness, and that the increment of roughness restrains the development of conical vortices formed at the lower and higher zone of buildings from discussion of power spectra and root-coherence for fluctuating wind pressures. The paper quantifies the effects and makes appropriate recommendations.