In dense urban areas, the pursuit of outdoor thermal comfort is a development goal included in the city’s sustainable plan. The aim of this study is to evaluate the effect of promoting new green areas, at ground and at rooftop levels, in the thermal comfort of the surrounding urban area. The simulation was made based on a recently concluded requalification project in a Lisbon neighborhood. This project was used as a case study to evaluate the effects of the new vegetation areas at ground level on microclimate and urban comfort , while the work of  was used as a case study to investigate the effect of green roofs. The ENVI-met software is used to model the past and present (after requalification) scenarios, and a new scenario with green roofs. The simulation results indicate that the presence of new trees and shrubs results in: (i) increased urban comfort in the morning and in the afternoon resulting from the decrease in temperature; (ii) a reduction of up to 3° in the morning (9 h) and up to 3° in the afternoon (15 h); (iii) an increment of 10% in the relative humidity of the air, and (iv) a slight reduction in natural ventilation in both the morning and afternoon periods. The microclimate simulation results confirm that vegetation is a key element when planning for comfortable public spaces.