On October 13th, Tokyo Tatemono Co., Ltd. (8804:TYO) announced the establishment of a condominium redevelopment association for the “Kojimachi Sanno Mansion Reconstruction Project".

While the building name includes the word “mansion”, to those not aware, mansion in Japanese means condominiums.  

The Kojimachi Sanno Mansion is located a one-minute walk from Kojimachi Station on the Tokyo Metro Yurakucho Line.  It is located in the Bancho address, a sought after residential area in Chiyoda ward.

As the current building is over fifty years old, it has become decrepit with insufficient earthquake resistance, deteriorating equipment, piping and leaks, all of which is impossible to improve through repairs and renovations. 

In 2016, Tokyu Tatemono was selected by the building’s homeowner’s association to take part in the redevelopment, and since has been working with the strata-title owners to improve the project's business potential by gaining the city permissions to increase the floor-to-area ratio (in Japanese, yoseki-ritsu) and keeping momentum moving forward with owners of the individual units.

For the redevelopment, Tokyu Tatemono utilised the Tokyo Metropolitan Government's Comprehensive Design Project, a set of guidelines that allows developers to create privately owned, public spaces in exchange for being able to build more usable floor space above what existing zoning allows.

In Kojimachi Sanno Mansion’s case, Tokyu Tatemono will create a 70 square metre park space on the grounds and a 2-meter-wide open space adjacent to the public sidewalk to improve the safety and comfort of the area. 

As a result, the floor-to-area ratio (in Japanese, yoseki-ritsu) will be relaxed from approximately 590 percent currently to approximately 670 percent.   This will increase the usable floor space when finished from 8,165 sqm currently to 11,661 sqm post redevelopment. 

Tokyu will acquire the newly created floor space from the redevelopment association, and then begin sales of the space once construction is nearing end.

The redeveloped building will have a footprint of approximately 1,221 square meters, be 18 stories above ground and have 2 stories below with a reinforced concrete structure and a more modern earthquake resistant structure. 

The new structure will house 106 units when finished, up significantly from the existing 57 units in the current building.  The existing 4 retail spaces will not be replaced making the new building entirely made up of residential units. 

In order to create an appearance befitting the traditional mansion district of Bancho, part of the design of the common areas has been commissioned to the Hashimoto Yukio Design Studio. 

Construction is scheduled to be completed in the summer of 2026.

Further Reading:

Tokyu Tatemono Press Release (Japanese only; PR Times, October 2021)

Tokyo Government Comprehensive Design Project (Japanese only; Tokyo Metro Govt)