Building Code
Building Coverage Ratio
Building coverage ratio controls how much of a site may be occupied in plan. It is a footprint rule, not a total-floor-area rule.
- Japanese Term
- 建蔽率
- （けんぺいりつ）
Overview
Editorial ExplanationBuilding coverage ratio, 建蔽率（けんぺいりつ）, is the ratio of 建築面積 to 敷地面積 and controls how much of the site is covered at ground level.
Building coverage ratio corresponds to the Japanese term 建蔽率（けんぺいりつ）. It describes the relationship between building area, or 建築面積, and site area, or 敷地面積. The rule is primarily about ground coverage, open space, fire safety, and the character of the block. It should be distinguished from Floor Area Ratio, which concerns total floor area.
It preserves open space, daylight, ventilation, fire separation, and block openness by preventing the building footprint from filling the entire site.
Exam Snapshot
Exam Reference- 1Write the formula first: building coverage ratio = building area / site area.
- 2When the problem mentions corner lot, fire district, or fire-resistant construction, check the condition before applying any relaxation.
- 3Separate coverage questions from FAR questions: 建築面積 points to coverage, 延べ面積 points to FAR.
- 4Understand the preconditions for relaxation rather than memorizing only the final percentage.
Required Terms
Core Diagram
Editorial ExplanationCore Concept
BCR controls how much of the site is covered by the building footprint.
Exam Solving
150 m2 site, designated 60%, corner relief +10%: max building footprint 105 m2.
Common Mistake
The numerator of BCR is building footprint, not the sum of all floor areas.
Future Diagram
Key Formula
Editorial ExplanationBuilding Coverage Ratio
Building Coverage Ratio = 建築面積 ÷ 敷地面積 × 100%
Educational formula only. Building-area treatment, relaxation conditions, and local rules require formal confirmation.
- 建築面積（けんちくめんせき）
- The building area or footprint used for the ratio. What counts must be checked under Japanese rules.
- 敷地面積（しきちめんせき）
- The site area used for calculation.
- Designated coverage ratio
- The permitted coverage ratio set by zoning or planning controls.
- Corner lot relaxation
- A possible relaxation, often studied as +10%, when corner-lot conditions are satisfied.
- Fire-district relaxation
- Fire-resistant buildings in fire prevention districts may involve relaxation, but conditions must be checked.
Variables & Terms
Editorial ExplanationVariables
- 建築面積（けんちくめんせき）
- The building area or footprint used for the ratio. What counts must be checked under Japanese rules.
- 敷地面積（しきちめんせき）
- The site area used for calculation.
- Designated coverage ratio
- The permitted coverage ratio set by zoning or planning controls.
- Corner lot relaxation
- A possible relaxation, often studied as +10%, when corner-lot conditions are satisfied.
- Fire-district relaxation
- Fire-resistant buildings in fire prevention districts may involve relaxation, but conditions must be checked.
Terms
- The basic relationship is building coverage ratio = building area / site area. The precise treatment of what counts as building area must be checked under Japanese rules.
- Coverage ratio controls the footprint of a building in plan. It affects open space, ventilation, daylight, fire separation, and perceived urban density.
- Coverage ratio and FAR answer different questions: coverage concerns the footprint, while FAR concerns total floor area.
- Corner lot relaxation is a common study topic. A corner location may allow a relaxed limit only when specific conditions are satisfied.
- In fire prevention districts, fire-resistant buildings may also be associated with relaxation concepts. The condition is not automatic and must be read carefully.
Applicability Check
Editorial Explanation- First identify site area and building area, then calculate building area divided by site area.
- Check the permitted coverage ratio for the zoning or planning condition.
- Then check whether corner lot relaxation, fire district conditions, or fire-resistant construction conditions may apply.
- Example: on a 100 square meter site with a 60% coverage limit, the study-level footprint limit is about 60 square meters.
- For real projects, projections, balconies, eaves, basement parts, local ordinances, and municipal interpretations must be checked separately.
Calculation Process
Editorial Explanation- Step 1
Confirm site area
Start with the 敷地面積 used in the problem or project data.
- Step 2
Confirm designated coverage ratio
Read the coverage limit from zoning or planning conditions.
- Step 3
Check corner lot relaxation
Determine whether the site satisfies corner-lot conditions. Do not apply +10% automatically.
- Step 4
Check fire-district relaxation
Check whether fire-resistant construction in a fire prevention district is relevant.
- Step 5
Calculate usable coverage ratio
Apply only the relaxations supported by the problem conditions.
- Step 6
Calculate maximum building area
Maximum 建築面積 = 敷地面積 × usable coverage ratio.
Worked Examples
ExampleBasic Example
Problem
200㎡ site, 60% coverage
- Step 1Maximum 建築面積 = 200㎡ × 60% = 120㎡.
Answer
This is a footprint calculation, not total floor area.
Exam Example
Problem
150㎡ site with corner relaxation
- Step 1Designated coverage ratio is 60%, and the site satisfies a +10% corner-lot relaxation.
- Step 2Usable coverage ratio = 70%.
Answer
Maximum 建築面積 = 150㎡ × 70% = 105㎡.
Examples
Example- A 100 square meter site with a 60% coverage limit allows a rough footprint of 60 square meters for study purposes.
- If the same site has a FAR of 200%, that does not mean the ground floor can cover 200 square meters. Ground coverage is still controlled by coverage ratio.
- An exam problem may mention a corner lot or fire prevention district, but the relaxation depends on the given conditions, not on the label alone.
Comparison Table
Editorial ExplanationStudy Table for Coverage Relaxation
| Condition | Study Reading | |
|---|---|---|
| Normal | Designated coverage ratio | Use the planning limit without addition. |
| Corner lot relaxation | Designated ratio + 10% | Common study pattern; conditions and local rules must be checked. |
| Fire-resistant building in fire prevention district | Possible relaxation depending on conditions | Not automatic for every building in a fire prevention district. |
| Corner lot + fire-district condition | May be combined | Combination and exact treatment require formal confirmation. |
Building Coverage Ratio vs Floor Area Ratio
| Building Coverage Ratio | Floor Area Ratio | |
|---|---|---|
| Controls | Ground-level footprint | Total floor-area density |
| Numerator | 建築面積 | 延べ面積 |
| Design effect | Footprint, open space, fire separation | Total volume, floor-count possibility, density |
| Common misunderstanding | Mistaken for total floor area | Mistaken for site coverage |
Exam Preparation
Exam Reference- Write the formula first: building coverage ratio = building area / site area.
- When the problem mentions corner lot, fire district, or fire-resistant construction, check the condition before applying any relaxation.
- Separate coverage questions from FAR questions: 建築面積 points to coverage, 延べ面積 points to FAR.
- Understand the preconditions for relaxation rather than memorizing only the final percentage.
- Check decimal and percentage conversion carefully.
Common Mistakes
Editorial Explanation- Confusing coverage ratio with FAR: coverage uses building area, while FAR uses total floor area.
- Applying corner lot relaxation simply because a site is at a corner.
- Assuming every building in a fire prevention district receives a coverage relaxation.
- Ignoring what is included in building area.
- Treating coverage ratio as a direct floor-count rule.
Memory Tips
Exam Reference- Coverage ratio asks: how much of the ground is covered?
- FAR asks: how much total floor area is stacked?
- When you see corner lot or fire district, check conditions before applying relaxation.
Next Topic
Related Glossary
Related Code Topics
Further Reading
- Building Standards Act Article 53
- e-Gov Building Standards Act
- MLIT building regulation materials
Official Source
建蔽率
建築基準法 第53条（要最終確認）
Official Source
建蔽率
建築基準法 第53条（要最終確認）
- Regulation
- 建築基準法
- Article Number
- 建築基準法 第53条（要最終確認）
- Note
- 建蔽率制限の根拠条文として扱う学習用参照。条文番号と適用条件は最終確認が必要。
- Verification State
- Draft
- Last Reviewed
- Not Reviewed
建蔽率
Guide reference
Government Guide
建蔽率
Guide reference
- Regulation
- 国土交通省 建築基準法集団規定資料
- Article Number
- Guide reference
- Note
- 国土交通省の集団規定に関する説明資料。建蔽率制限を理解するための政府ガイドであり、条文そのものではない。
- Verification State
- Draft
- Last Reviewed
- Not Reviewed
Educational Disclaimer
This content is provided for educational purposes. It is not legal advice and must not be used as the sole basis for permit applications, design approval, or legal determinations. Always consult official sources, local regulations, and qualified professionals.