The purpose of the study is to identify the major impacts on housing supply and transportation according to the alleviation of floor limitation in apartment remodeling and to present improvement of current policies. Apartment remodeling policy allowing to the alleviating height control(vertical extension) is to allow constructing two to three floors higher than the existing building, increase in the 15 percent of households, and selling out the increasing parts of the apartments. The method is to review impacts on possible infringement of the right of daylight sunshine amount and problems of FAR management according to floor number increase. And, it is to identify parking difficulties and transportation impacts according to the increase in the number of households and cars. It is, then, to identify securing feasibility according to parcel out of the extra apartments. Finally, it is to identify possible number of housing supply reviewing the physical condition of the apartment sites.

Its impacts are identified on the first building with 90 percent and more, second and third buildings with 50 percent and more in terms of the infringement of day light amount from remodeling. Thus, it is difficult of the apartments with 3 buildings or less to do vertical extension remodeling. In order to do vertical extension remodeling for the apartments in a district plan with height control, there should be a rest of 15 percent more below legal FAR in the existing sites. Buildings needed structure reinforcement are apartment sites with earthquake-proof design standard, 16 percent and apartment sites falling short of current earthquake-proof design standard, 71 percent respectively. The possible numbers of housing supply, satisfying physical condition and project possibilities are currently 40,964 units and 55,625 units for the future in year 2024 standards. As a result of the transportation environment effect in Seoul due to the increase in the number of vehicles on the roads, it is shown that gross trip distance increases between 0.14 and 2.16% currently and gross trip time, 0.25~3-83% respectively while gross trip distance increases 0.17~3.83% and gross trip time, 0.30~6.31% in 2024. It becomes different in terms of transport effects on road by the increase in household sizes and choice of transport modes. However, the increase in the use of public transit can solve this kind of transport problems.

Policy directions are focused on securing citizen safety, solution to the inconvenience of the life, sustainable development, and lengthening the longevity of housing. And policies are improved so as to shift from profitability, to manage considering a life cycle of apartments, to differentiate public supports about vertical extension and repair-type remodeling, and to maintain institutional amendments. Improvements related to the right of daylight sunshine amount are needed to readjust rationally the control of the right and to minimize unqualified buildings due to the applying of the new standard. Parking space is sufficiently secured toward increase in the number of the households, however problems related to the traffic volume in the sites can be solved by inducing public transit usage. Besides, these are recommended to pursue demonstration projects by the public in order for low-cost type remodeling to settle down, to encourage cost savings applying various public supports, to reinforce administrative organization.