Natural ventilation is held as an imperative for sustainable use and conservation of energy through passive cooling in buildings in the tropics. It is believed to be dependent on characteristics of the site, orientation and architectural characteristics of the building as well as wind direction. This study sought to ascertain the extent to which building orientation and opening size, as architectural characteristics, affect natural ventilation in office buildings planned around an open courtyard in Yola. The five office buildings in Adamawa State Urban Planning and Development Authority were the subjects of the Causal Comparative or ‘Ex-post Facto’ research design. Hot-wire anemometers were deployed to observe wind speeds at wind ward sides and inside of selected spaces; and wind directions were observed with an improvised wind vane. Data of spaces with different orientations were grouped; Analysis of variance (ANOVA) was employed to compare and draw inference on difference of mean wind speeds and ventilation coefficients among grouped spaces (p = 0.05). It was established that natural ventilation of the study office buildings was significantly different among spaces of different orientations and opening sizes. Space opening size expressed both in terms of total opening size relative to floor area, and in terms of ratio of outlet to inlet ranging from 12.7% and 0.57 to 30.6% and 2.50 were found to produce ventilation coefficients ranging from 0.06 to 0.50 in the study offices. Ratio of outlet to inlet was found to have more notable effect than total opening relative to floor area on ventilation coefficient. It was however found that natural ventilation was inadequate for thermal comfort in the buildings in hot dry climate of the study area. The study concluded that natural ventilation in the study area should be enhanced by orientating building openings about right angles to dominant wind direction to maximize air flow into interior, and optimizing opening size.
Key Words: Natural ventilation, Office buildings, Building orientation, Opening size, courtyard, Passive cooling