To wrap up the previous discussion through the chapters, it is necessary to mention, “building codes” that different countries proposed based on damages which happen during an earthquake can only be resolved by applying a “structural engineering solution”. However, based on experiences from previous earthquakes there is a definite connection between collapses or damages that to buildings and architecturally inclined design. In addition, to convey a degree of architectural expression of some aspect of earthquake action or resistance, a phrase was created by Christopher Arnold (Arnold 1996) as “an earthquake architecture”. Hence, architects who work at seismic regions are expected to give serious consideration to “earthquakes” within design principles next to the more ordinary facts such as customer demands, function, aesthetics etc. This issue has to be taken into consideration even through, the engineers check the final design and solve some of the problems during the detailing stage. Nevertheless, most of interior modification either by architect/interior architect or any other occupant of the building which is done without consulting with engineers may provide some serious problem and damages in the building in the event of an earthquake. As a fact, from the vision of an interior architect the main object of design is the existing buildings. Hence, many issues related to the structure and construction of existing buildings before modifications has to be taken into serious consideration. Consulting with expert engineers is strongly necessary and recommended before any modification or application on an existing building. The present study tried to reveal the importance and potential of interior changes on the overall lateral performance of structures as well as architectural consequences. Several structural deficiencies are also discussed and their relation to “interior change – seismic performance” is investigated. In addition to the above, two case studies are conducted on the issue. The most noteworthy or essential part to be considered by architects in terms earthquake is the code for dealing with “irregular building”, therefore, the focus of this study is on the most important problem regarding interior changes is the possibility of creating “irregular building” or applying modification without considering irregularity of existing building. This may become a serious issue in the case of old buildings – which are more likely to undergo changes and, which are more vulnerable against earthquakes – and careless change application. On the other hand, it is quite possible to correct – at least partially – the performance of a building by executing some architectural modifications, such as the resulting performance of the building being better than the original structure. In case No. II (palm beach hotel) we can see wonderful co-work between architect and engineers who are solving some of the important problems like soft floor and short columns by designing static structural elements as well as injecting chemical material into structure to increase the strength of the structural members. In addition, other significant issues which need to be taken into consideration for later interior modification on the project are using light material and structure which together effects on earthquake resistance of buildings. Based on this issue, open building became an important concept especially in countries like Japan with higher risk of earthquakes. Hence, interior modification especially done on residential buildings without consulting experts, the role of an architect in further modifications is extremely important. Architects in earthquake region have to consider important issues such as flexibility and adaptability during the design process of a building to offer some possibilities for future modification by occupants without creating any problems related to earthquake resistance of buildings. As pointed out in case No. I any modification without considering that the building is located in hazard zone may put the building in critical situation.