The number of the application of medium-risemulti-story wood buildings has been increasing. In west European countries, such as United Kingdom, Switzerland, Sweden and Austria. Timber it self is a good medium of CO2 stock. Therefore, it is as sumed that the urban area has the potential to be a huge CO2 stock when the application of timber-derived structure is widened. In the urban area, most of the buildings have multi story ?oors and by now, the knowledge has been accumulated in the ?eld of middle-rise multi story buildings made of timber. The author thinks it ideal for the timber structure to be exposed to the air, in order not only to let the structure expose to the air and release the humidity but also for the users of the building to detect the damaged area immediately. In the architectural planning, on the otherhand, it is often the case that a building has its structure inside of a wall. In this research, in order to increase the ways of application of timber to buildings,the target is set to create a structural system which is composed of timber and steel. As frame structure is more common in high-rise buildings, the system targets to apply to tall buildings which have more than five stories. The building physics issue is not within the scope of this research, and is discussed only qualitatively.