In the construction industry, many individual trades have to work simultaneously. This creates many potential difficulties on the construction site, primarily in relation to efficiency loss and construction period extension. To improve efficiency, a new interior finishing system for dwelling was developed. By using the system, both interior finishing and building services system are well combined. It is a well-known fact that the repetitive nature of construction produces a learning effect, which reduces both the overall working period and labour man-hours utilized. However there is little learning data available that is specifically related to interior works. Therefore, using the developed method, an observation study was conducted in order to collect learning data in an 11 storey housing construction project. The analysis demonstrates that a typical learning effect was found in 11 recorded repetitions.