This is a renovation project of single-family house, originally used as a typical two-story apartment-house with eight small rental units in the suburban area of Tokyo, Japan. More than half of the units of this old wooden apartment were empty, therefore the owner wanted to demolish it and then build a new single-family house (parents and two girls) at the beginning. However, architect Kazuyasu Kochi proposed to renovate this existing building into a single-family house instead of demolishing it, because with their budget Kazuyasu Kochi thought the clients could only gain the half area of the existing building if they built a new one, which does not benefit them.
Link 1 (divisare.com)
Link 2 (Kochi Architect Studio)