Conserving building means that there is a clear significant value of this building. This value can be architectural, artistic, historic, or environmental. The wide concept of the conservation is to predict the possible risks around this valuable building to consider the appropriate actions for preserving it through different processes and interventions such as restoration.
Conserving of the cultural heritage can extend life of these valuable resources of past cultures as well as it can improve the economic conditions of a society. Taking into consideration that these resources of cultural heritage are non-renewable so the intervention should be able to achieve the contemporary requirements without altering intrinsic values of them \citep{magrini2016energy}.
Definitions of conservation are found in international conventions, national laws of each country. In this part, the definition of conservation is extracted from Venice charter, ICOMOS Burra Charter, Italian Code of the cultural and landscape heritage “Law number 42/2004”, and European Committee for standardization “CEN”.
Conservation is an overall concept to protect cultural heritage. It aims at protecting buildings, or site or even remains to keep their cultural significance. It includes three main activities as following; PRESERVATION, MAINTENANCE, RESTORATION, or any combination of these activities \citep{Mazzarella_2015}\citep{troi2014energy}.
Preservation means maintaining the fabric of a building in its existing state and  delaying the causes of deterioration. Also, preservation includes process of  applying measures necessary to sustain the existing form, integrity, and  materials of an historic property. So, the set of activities to decrease the  risk situations should be considered in each context.
Preservation is  suitable in two cases:
- If the existing fabric itself  constitutes evidence of specific cultural significance, or
- If insufficient information is  available to allow other conservation processes to be carried out.
It includes  preliminary measures to protect and sustain the stabilization of the building,  generally focuses on continue maintenance and repair of historic materials and  features rather than extensive replacement and new construction.
New exterior  additions, that transform the aspect of a building, are not allowed; however,  the limited and sensitive improving of mechanical, electrical, and plumbing  systems and other code-required work that make properties functional is  appropriate.
Restoration is returning the existing fabric of a building to a known earlier state. Thus, it is the process of accurately depicting the form, features, and character of a building as it appeared at a certain period of time. It is mainly focused on the preservation, recovery and enhancement of the character of this valuable building.
It is suitable in two cases:
- If there is sufficient  information of the earlier state of the building, and
- If returning the building to  that state discovers the significance of the building and does not harm or  demolish other parts of the building.
-  If the state of conservation is  very bad and there are several collapsed parts.
The restoration can be done by removing  features from other periods and reassembling existing components reconstruction  the missing features without introducing new materials or sometimes with the  use of materials and techniques recognizable from the original, as long as  consistent with the character of the buildings.
The limited and sensitive improving of  mechanical, electrical, and plumbing systems and other code-required work to  make properties functional is appropriate within a restoration project.
Maintenance includes activities and  interventions to continues protecting of the cultural property and to maintain  the integrity, efficiency, and functional identity.
Table A in Figure (7) summarize the concept of conservation (aim, variables, building category) and also Refer to A Glossary in the appendix file .