Non-invasive, scalable, building retrofit solutions are amongst the most likely large scale adoption techniques to assist in climate change adaptation in the existing built environment, particularly in university type buildings where rehousing live activities will prove costly. Natural ventilation is an attractive retrofit strategy due to the low impact nature of the installation. A number of internal environmental criteria that are important to ventilative cooling strategies can be substantially modified as a result of an external retrofit solution. These include ventilation rate, internal thermal stratification, diurnal thermal stability, surface and air temperature variations etc. More generally, additional factors that can influence single sided natural ventilation performance related to the building microclimate are wind speed and direction, outdoor temperature profile, turbulent characteristics of the wind and pressure differences across the building envelope. This paper presents results from full scale performance testing of the natural ventilation system of a deep retrofit solution applied to an existing 1970s precast concrete building in south of Ireland. The solution presented is modular, scalable, externally applied and incorporates opaque and transparent elements as well as integrated automated and manual ventilation openings. The paper outlines different operational configurations for the single sided natural ventilation system and the respective effect these configurations have on internal environment based on full scale testing under dynamic outdoors conditions. Results are based on data collected for two single sided, direct gain cellular offices, one in the existing building that has not been retrofitted which acts as the control space, and the other one retrofitted to a very high standard. Four different types of ventilation configuration are summarised. The findings show that thermal stratification has been found to be substantially modified post retrofit although the relative magnitude is still significant in the retrofit due to reduced indoor temperatures while the amplitude of diurnal indoor air temperature has been effectively eliminated. The ventilation rate is also considerably lower in the retrofit spaces under some configurations. Each configuration is classified based on findings.