courtyard lightweight roofs for historical buildings in iran; analyzing the current samples and proposing design guide models

there are several courtyards of historical buildings in iran that have changed their original function because of reuse and have adopted for physical adjustments of the renovation projects. usually they are covered by lightweight roofsand have been used as religious spaces, praying or audience halls, restaurants, exhibitions rooms, etc. unfortunately most of these lightweight roofs have inappropriate design or environmentalproblems.  in some cases they have damaged the building's walls, floors or finishing by their imprecise details. the roofs that were permanent and not temporarily erected and removed have unfortunately changed the role of an open central courtyard of the iranian architecture. this paper tried to investigate an appropriate design for a lightweight roof of historical building courtyard in iran. the research began with a short study about historical background of lightweight roofs in iran. the second part of the paper is the study of different examples of the recent lightweight roofs of the courtyards in iran that were constructed in buildings such as mosques or houses. there are three types of lightweight structures of the surveyed courtyards: a) scaffolding structures, b) truss structures, and c) tent structures. these roofs are analyzed by five key factors: structural quality, environmental comfort, details, physical impacts on the building and visual appearance in the interior spaces. the third part of the paper is about the study of remarkable world experiences of convertible membrane roofs for courtyards of historical buildings. our selection is based on importance of the designer of the roof or the building itself or numerous citations of such structure. physical contact between these kinds of roofs and the buildings is crucial. therefore these roofs are categorized into four types: a) roofs that the contact point of their elements are outside of the buildings, b) on top of the roof, c) tresses from wall, and d) placed inside the courtyard. these roofs are analyzed by three key factors: movement specifications of the roof, construction details and visual appearance in the interior spaces. at the end of the second and third parts of the paper the roofs that were not harmonized or could not adapt with geometrical and physical aspects of iranian historic courtyards were eliminated. in the fourth part of the paper the design guides for erective and removable or convertible roofs were proposed. these guides were categorized based on the analysis of the iranian and world experiences. at first, different design guides for lightweight roofs that can be easily erected and removed were represented in a table.  second, different design guides for convertible lightweight roofs based on the world experiences were presented in another table. what is presented in this paper as design guide model of erected and removed or convertible roofs had mainly focused on the geometrical aspects and main construction elements of these lightweight roofs that can be adapted with iranian historical courtyards. the mechanical and technical aspects and appropriate details of these roofs are the future trend of the research.