Abstract
Khosf county with a hot-dry climate is located in South Khorasan province in eastern Iran and on the eastern edge of the Lut desert. Despite the existence of historical monuments in this region of Iran, little is known about them to archaeologists, urban planners, architects, and art historians. Special attention was paid to the historical urban fabric and residential houses which are mainly related to the late Qajar and early Pahlavi eras, in the archeological survey conducted by the authors in the Khosf region in 2014. Three relatively intact and well-established historical urban fabric in the city of Khosf and the villages of Khor and Noghab were studied during this study and 45 historical houses in these areas and other historical villages of Khosf were examined. The studied historical/traditional fabrics are mostly active and today with some changes in the body of the building, they are still used by the local people of the region. The method of this research is descriptive-analytical and the way of collecting data is also based on archaeological studies in the region to document and collect information about traditional houses of Khosf, and Then based on library studies. This research seeks to answer three main questions: 1- How much has the climate affected the type of structures and architectural components of traditional Khosf houses? 2- Do these conditions prevent the influence of the changes and developments of the common architecture of the Qajar and Pahlavi periods or not? 3- And what have been the common decorative techniques in the architecture of Khosf houses? Based on the research questions, the main objectives of the present study are to investigate the impact of the climatic conditions of the region on traditional houses Khosf and developments in Iranian architecture, as well as the study of different structures and architectural components of these buildings and their related decorations. Despite the general resemblance to traditional architectural patterns in hot and dry regions of Iran, the results show that it is strongly influenced by the climate of the region and in terms of architectural structure and related decorations is slightly affected by Qajar to Pahlavi period architectural developments..
Keywords: Khosf, Residential House, Qajar, Pahlavi.

Introduction
Man has always had many buildings from distance past, many of which have been destroyed over time. Among these, residential houses are the most important and abundant architectural structures that have always been built or reconstructed by humans. But these buildings are generally destroyed over time and turned into a pile of soil. Therefore, it is necessary to study and document the remaining traditional and historical buildings of the country and study their construction and decoration methods and topics such as the impact of climate on them. In Iran, due to the richness of the country’s historical antiquity, many relics of traditional houses and urban fabrics have been left. At present, most of the ancient houses in Iran mainly belong to the Qajar to the first Pahlavi period. Many studies have been done on the architecture of traditional houses in different parts of Iran, which are mainly based on the historic and magnificent houses of Yazd and Kashan, but less attention has been paid to the study of simpler houses in small towns and suburbs. One of such areas where a large number of traditional/historical houses and to some extent some of its traditional fabrics have survived is the city of Khosf in South Khorasan Province, where no independent research has been done on the urban fabric and historical houses. Accordingly, the present study is the first step in studying and analyzing these architectural spaces. in this study, 45 historical houses located in three historical contexts of Khosf city and Noghab and Khor villages and surveyed by the authors in 2014 are considered as the statistical community. Considering that traditional houses, in addition to using the knowledge of their predecessors, have also been affected by climatic conditions and changes in Iranian architecture, it is necessary to know the extent of these effects in different regions. The main objectives of the present study, based on research questions, include the study of the decorations, structure, and various architectural components of traditional Khosf houses and recognizing their impact on climatic conditions and architectural developments in Iran.
Research Questions: The present study seeks to answer three main questions: 1- How much has the weather condition affected the type of structures and architectural components of urban fabrics and traditional houses of Khosf? 2- Do these conditions prevent being affected by the changes and developments of the common architecture of the Qajar and Pahlavi periods or not? And 3- What are the common decorative methods in the architecture of Khosf houses and how have they been?
Research Method: The method of this article is a descriptive-analytical one and the method of collecting data is also based on archaeological studies in the region to document and collect information about traditional houses in Khosf and then Based on library studies.

Article Text
With a hot and dry climate, Khosf is one of the southwestern counties of South Khorasan province, which is located in the eastern margin of the Lut desert. In most parts of the year, most of this area sees wind that has direct and indirect effects on the type of architectural structure of the region. Archaeological study of Khosf county has resulted in the identification of 45 residential buildings that date back to the Qajar to the early Pahlavi period. These buildings were identified in different parts of the county, from mountainous and foothill areas such as Ark and Bein Abad to desert areas such as Khosf, Khor, and Noghab. According to the objectives of the present study, Khosf traditional houses are studied based on the principles of traditional Iranian architecture such as urban form, introversion, direction, scale, spatial hierarchy, and architectural components of houses such as the entrance, courtyard, building materials, plan, colors and decorations and the effect of climatic conditions of the region and Iranian architectural developments on these works were investigated. For example, in terms of direction, most of the traditional houses of Khosf have been built in the northeast-southwest direction, and climatic issues such as the direction of the sunshine and the direction of the wind have had a direct impact on this choice. On the other hand, the studied buildings have a compact plan as much as possible and try to keep the external surface of the building smaller than its volume. This density and compactness of the house plan minimize the amount of heat exchange through the outer walls of the building in both summer and winter, thus preventing the penetration of heat into the building in summer and its loss in winter. Also, many of the studied buildings had one-way wind deflectors that brought cool air into the house in summer. Other features of the traditional Khosf houses include: having a central courtyard and rooms around it, having two porches on either side of the courtyard, having one or more windbreak rooms, having a room fireplace for winter, use of local and traditional materials, have very little decoration such as plastering or brickwork. 

Conclusion
Khosf is one of the hot and dry cities on the eastern edge of the Lut Desert that is directly affected by this climate. From the past until now, this county has largely preserved its traditional identity in the construction of various architectural works, due to its distance from very large cities. One of these works is the traditional houses of this county, which currently have a large number of them in areas such as Khosf, Khor, etc. Given that these houses have not yet been studied and surveyed, and at the same time have largely retained their traditional texture, it was necessary to address them in an independent study. Accordingly, the present study was conducted with the general purpose of studying traditional and old houses in Khosf city and with other purposes such as investigating the role of climatic and traditional factors in the formation of various spaces of these buildings. According to these studies, it can be concluded that the traditional houses of Khosf show their great influence on the climate and geographical conditions of the region. This issue can be observed in various factors such as the direction of the construction of alleys and their dimensions, direction of the construction of buildings, location of rooms in a building, type and number and direction of the windbreak, number and structure of porches, dimensions of rooms, little use of opening spaces such as windows, etc. Of course, with some factors such as the isolation of the Khosf region, its distance from the main route of commercial and communication highways, and its lack of proximity to major cities, this city will benefit less from the architectural and urban developments of the Qajar and Pahlavi periods. This issue is seen in the introverted architectural structure of buildings as well as related decorations. Accordingly, the traditional architectural model of this region can be introduced as a traditional, indigenous, and unique model, and it is necessary to take more measures for the continuation and further prosperity of this model.