Tokyo, Floor Area and Sunlight Rules
Tokyo’s building rules, an instructive foreign comparison for the rules of buildable ground Michael Stern writes on, are easiest to read on foot, and the walk below starts at the Marunouchi exit of Tokyo Station. The red brick station building there was completed in 1914 to Kingo Tatsuno’s design, runs about 350 metres along its front, and stands three stories high under two domed roofs, as the government magazine Highlighting Japan records.2 Everything around it is ten times taller, and the reason is a number painted on the planning map.
Standing at the Marunouchi exit
The station is low by choice and by law. Air raids in 1945 burned off its third floor and the postwar rebuild left it at two stories; the restoration finished in 2012 put the third story and the domes back, reusing original bricks and cast stone wherever they could be saved, and slid 352 rubber isolators and 158 oil dampers under the 70,000 tonne building while temporary piles held it up.2 Tokyo Station City adds the finishes: new face bricks fired to match the surviving ones, a natural slate roof with Japanese slate on the domes, and relief work in the dome ceilings rebuilt from fragments found above a postwar duralumin ceiling.3 The building is an important cultural property, which fixes its height for good.3
Turn around and the contrast is the lesson. The OMY Council, the body that coordinates the Otemachi, Marunouchi and Yurakucho district, lists designated floor area ratios of 700, 900, 1,200 and 1,300 percent across 103 buildings on about 120 hectares, served by 28 rail lines and 13 stations carrying roughly 1.17 million passengers a day.4 A ratio of 1,300 percent means thirteen times the site area in floor space, so a three story station on a large site leaves most of the floor space the map allows unbuilt, and that gap is what the district’s special tools exist to use.
The district around the station
- District area
- 120 ha
- Buildings
- 103
- Designated floor area ratios
- 700 to 1,300 percent
- Rail lines serving 13 stations
- 28 lines
- Train passengers a day
- 1.17 million
- Special floor area ratio district transfers, covering 9 buildings
- 2 projects
Across the street: the rebuilt Marunouchi Building
The first tower on the walk is the Marunouchi Building, which The Japan Times reported reopening in September 2002 after a rebuild announced in 1995 and begun in 1999, 76 years after the original went up: 37 floors and four basements, about 180 metres tall, roughly 160,000 square metres in all, with shops and restaurants low down, conference rooms on the seventh and eighth floors and offices from the ninth to the 34th.1 The OMY Council’s data sheet records how buildings of that size are made lawful here: ten projects used integrated design, four used the special district, twelve used special districts for urban regeneration, two used the special floor area ratio district across nine buildings, and two exchanged uses between buildings.4 The special floor area ratio district is the Tokyo relative of the transfers described in this site’s entry on transferable development rights: inside one such district, floor area that a site will never build may be counted toward another site.
Out to a residential district: the two ratios
Leave the office towers behind and the arithmetic changes scale. Plaza Homes, a Tokyo property firm writing for foreign buyers, explains that every site carries two ratios set by its land use zone: the building coverage ratio, the footprint as a share of the site, regulated between 30 and 80 percent to keep gaps for fire, evacuation, light and air; and the floor ratio, total floor measured against site area, regulated between 50 and 1,300 percent to hold down population, traffic and demand on sewers and power.5 A 100 square metre site at 50 percent coverage and 300 percent floor area ratio allows a 50 square metre footprint and 300 square metres of building.5
The width of the fronting road counts as much as the zone. On a road narrower than 12 metres, the permitted ratio becomes the lower of the zoned figure and the road width times 0.4 in residential zones or 0.6 elsewhere, and where the road is under 4 metres the site boundary is set back to widen it, with the lost strip no longer counting as site area.5 Balconies, lofts, porches and shared elevator halls are left out when floor area is totted up, and basements and built in garages are partly discounted.5 New York readers will recognise the exclusions from this site’s FAR mechanism page, and the road width rule as a cousin of the street relationship New York once drew as a sloping plane above the sidewalk.
How a Tokyo site is sized
- Use districtOne of 13 districts, eight of them residential, sets the permitted uses and the two ratios.
- CoverageBuilding coverage ratio caps the footprint at 30 to 80 percent of the site, with 10 percent extra on a corner lot or for a fireproof building.
- Floor areaFloor area ratio runs from 50 to 1,300 percent by district and caps total floor against the site area.
- Road widthOn a road narrower than 12 metres, residential sites take the road width times 0.4 and other sites times 0.6 if that is lower.
- SetbackA road under 4 metres wide pushes the boundary back to widen it, and the lost strip no longer counts as site.
- ExemptionsBalconies, lofts, shared elevator halls and stairs, and part of a basement or built in garage stay out of the count.
The thirteen districts and the slant planes
Touwa, a builder of custom houses, lays out the seven axes a designer checks before buying land: use district, coverage, floor area, slant line limits, height limits, fire districts and road frontage.6 There are 13 use districts, eight residential, two commercial and three industrial; a Category I low rise exclusive district allows about two stories under an absolute height of 10 or 12 metres, while commercial districts run to 80 percent coverage and 1,300 percent floor area.6 Corner lots gain 10 percent coverage, fireproof buildings in a fire district gain another 10, and the two can stack.6
The slant planes shape the roofs. Touwa describes three: a road diagonal that climbs from the opposite boundary of the fronting road at 1 to 1.25 in residential districts, an adjacent site diagonal rising from the neighbour’s boundary, and a north side diagonal in residential districts that protects the northern neighbour’s sun.6 These planes are the usual reason a third story, penthouse or loft is given up, and the designer’s skill lies in the sky factor relaxation, which allows a building past the plane where it can show equivalent light and ventilation.6
The shadow test on a winter afternoon
The rule that most surprises visitors is the sunlight regulation. The Great Planet traces nisshoken, the right to sunlight, to the 1970s, when fast vertical construction left lower floors in permanent shade, residents in affected neighbourhoods went to court, and the law came to hold that buying land does not include the right to take a neighbour’s sun.7 Before approval, a developer must calculate the shadow a proposed building will cast on adjacent sites across the winter solstice, the shortest day, and a scheme that shades neighbours beyond the legal threshold is stopped; the same article recalls a Nagoya case in which a building that met every zoning and height rule was halted because it would have shaded its neighbours for more than five hours a day.7 Touwa confirms that mid and high rise residential districts carry this shadow limit at the solstice and that half basements, sloped roofs and lowered eaves are the usual ways to keep volume inside it.6
Two ways a building loses its top
| Slant planes | Sunlight regulation | |
|---|---|---|
| What it measures | A sloped envelope rising from the road or the neighbour's boundary, 1 to 1.25 from the opposite road edge in residential districts | Hours of shadow a building casts on neighbouring sites at the winter solstice |
| Where it applies | Most districts; low rise exclusive districts use an absolute 10 or 12 metre cap instead | Mid and high rise residential districts, with thresholds by district |
| Typical result | A third story, penthouse or loft that has to be given up | Roofs that lean back as if sliced, asymmetrical tops, tapered masses |
| Relief | The sky factor method, exceeding the plane where equivalent light and air are secured | None at the threshold; a scheme over the limit is halted |
| Origin | The Building Standards Act | The 1970s, after residents in shadowed neighbourhoods went to court |
The end of the walk
The walk ends on a residential street in the west of the city, under a block of flats whose top floors lean back as if cut by a blade. The Great Planet describes exactly that skyline, roofs at odd angles and masses that taper into funnels, as the physical trace of the shadow law rather than any design fashion.7 Read together, the station, the office tower and the sliced roof show one system with three expressions: a ratio that fixes volume, planes and shadows that fix shape, and districts that let unused volume move. New York handles the same three questions with recorded easements that protect light and air and transfers between adjoining lots; Tokyo writes the sun into the code.
