Environmental heat stress on buildings through façades contributes to indoor overheating and thus increases demand for energy consumption. The study analyzed the problem, heat gain risk, of modern air-conditioned multi-level office buildings in tropics, for example Colombo. Plan form, orientation, sectional form and envelope were identified and theorized to understand design interventions to reduce the risk of getting heat stress on indoor environments. On-site thermal performance investigations in multi zones of identified three typical built forms, namely; shallow, deep and covered atrium plan forms, quantified the heat stress. Reaching the daytime indoor and surface temperature in peripheral zones of multi-story office buildings during air conditioning “off-mode” up to 38 °C–42 °C was seen as a critical heat stress situation to be addressed through building design. Shading or insulation on façades to control environmental heat gain and manipulation of building section for night ventilation to remove internal heat developed during the daytime are discussed. However, the significance of the plan form depth was found to be a main contributor in dealing with heat transfer to indoor space. Deep plan form was found to be more effective in controlling environmental heat transfer to indoor space across the plan depth.