Thorough explanation of the building coverage ratio and floor-area ratio of real estate

What is a building coverage ratio and floor area ratio? Explanation and calculation methods

Once we know the property's building coverage and floor-area ratio, we can calculate the size of the building that can be built on that land.
Restrictions on the building coverage ratio and floor-area ratio vary from area to area, and are fixed by the designated administrative agency (the mayor of the municipality where the building is located, and the governor of the prefecture where other municipalities are located).
You can check how much your land is worth through local government websites, the Urban Planning Section counter, and other means.
In the following items, we will introduce the method of calculating the building coverage ratio and floor-area ratio of real estate

Calculating the building coverage ratio

The building coverage ratio is calculated as follows:
Building coverage ratio = Building area ÷ Land area × 100%
The building area refers to the area when the building is viewed from the top, and this is called the horizontal projected area.
However, an area of 1m or less and the balcony is not included in the calculations.
Let's calculate by actually applying the numbers.br> For example, suppose you acquire 100 square meters of land in an area with a specified building coverage ratio of 80%.
The building area is calculated as follows:
Building area = 100 m2 × 80% = 80 m2
The building area to be built on the land acquired is 80㎡ or less.
The image is that when the building coverage ratio is low, there is space between the buildings, and when it is high, buildings are densely concentrated.
By setting limits on the building coverage ratio, sunlight and openness are secured, and an environment that is easy to live in is maintained

Calculation method of volume ratio

Balcony, veranda, etc. are not included in the total floor area.
Let's calculate by actually applying the numbers.
For example, suppose that you acquire a 100 square meter land that has a floor area ratio specification of 400%.
The total floor space is calculated as follows:
Total floor area =100㎡×400%=400㎡
The total floor area of buildings built on acquired land is 400 m2 or less.
The image is that the lower the floor-area ratio, the smaller the building is, the lower the floor-area ratio, and the larger the building is, the higher the floor-area ratio.
However, if only buildings with high floor-area ratios, such as high-rise condominiums, are built, the infrastructure will become unstable due to overpopulations.
The floor-area ratio was created to control the residential population and maintain a comfortable living environment.
Please note that the floor-area ratio does not necessarily apply the upper limit determined by the government.
Details are given in the application area chapter.

Building coverage ratio and floor area ratio - Relationship with Zoning Districts

We must not forget about restrictions placed on real estate by the local government.
When housing, commerce, and industry conglomerate in the same area, there are many problems such as smells and noise.
Areas and regions are divided into 13 zoning areas according to their use.
Since the government designates the range of building coverage ratio and floor-area ratio by zoning, there is a deep relationship between the two.
The following section explains the relationship between the building coverage ratio and volume ratio and zoning.

Building coverage ratio and floor-area ratio by zone

In residential use areas, the building coverage ratio and floor-area ratio are determined as follows.
If you recall, you can estimate how much volume will be built by listening to the area of use.
Category 1 Low Rise Exclusive Residential Districts ・Category 2 Low Rise Exclusive Residential Districts

Building coverage ratio 30・40・50・60/ Floor Area Ratio 50・60・80・100・150・200
Category 1 Medium-to-high Rise Exclusive Residential Districts ・Category 2 Medium-to-high Rise Exclusive Residential Districts
Building coverage Ratio 30・40・50・60/ Floor Area Ratio 100・150・200・300
Type 1 Residential District ・Type 2 Residential District
Building coverage ratio 60/ Floor Area Ratio 200・300・400
Garden residential area
Building coverage ratio 30・40・50・60/ Floor Area Ratio 50・60・80・100・150・200
When looking for real estate, check not only the building coverage ratio and floor area ratio, but also the zoning area.
Once you know the zone area, you can know how large the neighboring buildings will be.
For example, a Class 1 residential area with a floor-area ratio of 400% can build a larger building than a Class 1 low-rise residential area.
Neighborhood buildings, however, should also have the same floor-area ratio, so there is a great deal of potential that future buildings built nearby will hinder sunlight and views.
In addition, the calculation of the floor area ratio requires attention when the width of the front road is 12m or less.
The result of the following formula and the specified volume ratio, whichever is less, are adopted.
Floor Area Ratio ＝ Width of front roads × Multiply according to zoning area×100%
The multiplier according to the application area is 0.4 for residential system and 0.6 for non-residential system.
For example, when the front road is 4m on land in a type 1 low-rise residential area
4m×0.4×100％＝160%
If the designated volume ratio is 200%, then 160%<200%, and the smaller 160% volume ratio will be adopted.

Building coverage ratio and floor area ratio - Mitigating provisions

Mitigating provisions have been established for the building coverage ratio and floor-area ratio, and if certain conditions are met, more buildings can be built.
This section summarizes the main relaxation provisions for the building coverage ratio and floor-area ratio.

Mitigating conditions for the Building coverage ratio

The building coverage ratio is a limit established to prevent a dense number of buildings in the same area.
For this reason, building coverage ratios can be relaxed for buildings that are firmly anti-deflationary measures and corner lands that have little contact with other buildings.
When the building coverage ratio is relaxed,  the designated building coverage ratio can be increased by 10-20%.
The following three cases are where conditions can be relaxed:
① Fireproof buildings in fire prevention areas other than those with 80% building coverage
② Buildings with anti-flame defensive performance equivalent to or greater than that of fire-resistant buildings, quasi-fire-resistant buildings, and quasi-fire-resistant buildings
③ Corner land designated by a specified administrative agency

If any one of the three cases is met, 10% is added, and if two combinations of ①, ③ or ②, ③ are met, 20% is added.
In addition, if the building coverage ratio is 80%, the building coverage ratio for fire-resistant buildings in the fire prevention area is 100%, which is not subject to restrictions.

Mitigation of Floor Area Ratio

The floor area ratio includes measures to exclude certain areas, such as underground rooms and built-in garages, from the total floor area.
It is possible to effectively utilize the excluded area in other areas, and the profitability of the expanded portion of the real estate will also improve.
In addition to those introduced here, balcony verandas, outlets, pouches, etc. will also be eased if certain conditions are met.

Basement
Underground rooms are excluded up to one-third of the floor area used as a house if the following conditions are met:
●The ceiling of the basement is 1m or less above the ground level.
●The basement is used for residential purposes.
●The height from the floor of the basement to the ground is 1/3 or more of the ceiling height.

Loft/attics
Lofts also have easing provisions.
It is excluded from the total floor area if the following conditions are met.
●The loft's ceiling height is 1.4m or less.
●Loft area is less than 1/2 of the floor area of the immediately lower floor
●Stairs are movable.

Garage
Warehouses attached to buildings can also be relaxed up to one-fifth of the total floor area, including garages.
It can also be used in conjunction with the relaxation of underground rooms described earlier.

In Conclusion

In this article, we have explained the building coverage ratio and floor-area ratio of real estate, focusing on calculation methods and mitigating provisions.
Both are important limits to maintaining a comfortable living environment in urban planning.
Furthermore, since the size of the building determines its value, it is also indispensable to calculate building size in conjunction with the income and expenditure of real estate.
It is possible to calculate the value more quickly if you remember the value with the application region and set.
In addition, it is common practice to build buildings by effectively utilizing mitigating provisions.
When we rent or buy or sell real estate, we can expect to see an increase in business potential.