Thus, PhD research topic tries to cover the  lack in achieving balance between the thermal comfort requirements and  conservation issues in historic buildings in hot arid zones. Ottoman historic  residential buildings in Cairo act as a case study for expanding this concept  to similar historic residential buildings in Mediterranean and hot arid zones.

STATE OF  ART    

The state of art is divided into four main  parts:
          5.1. Thermal comfort and historic buildings in different climate zones;    
          5.2. The  Ottoman houses (heritage and Society)    
          5.3. Discussion about the recent  researches about the used methodologies of measuring the thermal comfort in historic houses; then
          5.4. Conclusion and comments   

THERMAL COMFORT AND HISTORIC BUILDINGS IN DIFFERENT CLIMATE ZONES

Europe has the majority of the international researches that deal with thermal comfort and energy efficiency issues in the historic buildings. As shown in Figure (15), the case studies of these researches, are mostly about residential buildings (23%), then both and palaces religious buildings take (17%) each, then museums, theatres or libraries take(11%), and then the studies on urban area (such as neighbourhood, cities, countries) takes (10%). Most of those researches tackled the historic buildings that belong to the last two centuries \citep{martinez2016energy}.