Building Code
North-side Slant Restriction
North-side slant restriction, or 北側斜線制限（きたがわしゃせんせいげん）, protects daylight and living conditions on the northern neighboring side, especially in residential contexts.
- Japanese Term
- 北側斜線制限
- （きたがわしゃせんせいげん）
Overview
Editorial ExplanationNorth-side slant restriction, 北側斜線制限（きたがわしゃせんせいげん）, controls building height and upper massing from the northern neighboring side.
North-side slant restriction, 北側斜線制限（きたがわしゃせんせいげん）, is a Japanese height-envelope rule measured from the north-side neighboring boundary. It mainly protects daylight, ventilation, sky openness, and the living environment of northern neighboring residential sites. It is not a street-side rule, and it is not the same as shadow regulation, 日影規制（にちえいきせい）. Study it as a set: starting height, horizontal distance from the north boundary, slope ratio, and applicable zoning.
It protects daylight, ventilation, and the living environment of the northern neighboring site, especially in residential districts where upper mass can strongly affect adjacent homes.
Exam Snapshot
Exam Reference- 1Common exam point: Building Standards Act Article 56 paragraph 1 item 3. First check whether the zoning is one where north-side slant applies.
- 2Applicability keywords: 第一種低層住居専用地域, 第二種低層住居専用地域, 田園住居地域, 第一種中高層住居専用地域, 第二種中高層住居専用地域.
- 3Fill-in style keyword: true-north horizontal distance, 真北方向の水平距離. Do not reduce it to a generic distance.
- 4Numeric exam point: slope 1.25; low-rise residential and rural residential commonly add 5m, while mid/high-rise residential commonly adds 10m.
Required Terms
Core Diagram
Editorial ExplanationCore Concept
Read horizontal distance D from the north-side boundary and add the applicable base height.
Exam Solving
With D = 4 m, a 5 m base gives 10 m; a 10 m base gives 15 m.
Common Mistake
North-side slant is a geometric height plane; shadow regulation evaluates time-based shadow impact.
Future Diagram
Key Formula
Editorial ExplanationNorth-side Slant Restriction
Height limit = starting height + horizontal distance × slope
Educational formula only. Confirm zoning, district designation, municipal conditions, and current legal text before applying it to real projects.
- Starting height
- The base height from which the slant begins. In study examples, low-rise residential is often 5m and mid/high-rise residential 10m.
- Horizontal distance
- The plan distance from the north-side boundary to the relevant building part.
- Slope
- Commonly studied as 1.25; final application requires checking zoning, district designation, and current law.
Variables & Terms
Editorial ExplanationVariables
- Starting height
- The base height from which the slant begins. In study examples, low-rise residential is often 5m and mid/high-rise residential 10m.
- Horizontal distance
- The plan distance from the north-side boundary to the relevant building part.
- Slope
- Commonly studied as 1.25; final application requires checking zoning, district designation, and current law.
Terms
- Study formula: north-side slant height limit = starting height + horizontal distance from the north-side boundary × slope ratio. Final application requires checking zoning, district designations, and current legal text.
- Starting height, 起算高さ, is the base height from which the slant begins. It is not the total building height. For study, low-rise residential districts are often treated as 5m, and mid/high-rise residential districts as 10m.
- Horizontal distance is the plan distance from the north-side boundary to the relevant building part. The farther the building part is from the north boundary, the more height is generally allowed.
- The north-side boundary, 北側境界線, is the site boundary facing the northern neighbor. Marking north direction is the first step.
- The common study slope is 1.25. This is a learning simplification; actual application must be checked by zoning and law.
- Applicable zoning study table: 第一種低層住居専用地域, 第二種低層住居専用地域, 田園住居地域, 第一種中高層住居専用地域, 第二種中高層住居専用地域. Starting height may differ by district.
- Comparison: road slant protects street-side openness; north-side slant protects the northern neighboring residential environment.
- Comparison: north-side slant is a geometric slant plane; shadow regulation evaluates shadow impact over specified times.
- Design impact: it can shape roofs, upper setbacks, second/third-floor massing, north-side room planning, and height control in residential districts.
Applicability Check
Editorial Explanation- Step 1: identify north direction, the north-side neighboring boundary, and the site zoning.
- Step 2: check whether the zoning is one where north-side slant is important, and identify the study starting height. Low-rise residential districts are often studied as 5m; mid/high-rise residential districts as 10m.
- Step 3: identify the slope ratio. The common study value is 1.25, but legal and municipal confirmation is required.
- Step 4: apply the study formula to relevant building parts: height limit = starting height + horizontal distance × slope ratio.
- Step 5: include roof shape, upper floors, penthouse-like elements, attic volumes, and projections. Do not check only the highest overall point.
- Diagram Notes: a future diagram should label the north-side neighboring boundary, starting height, horizontal distance, slant plane, upper setback, roof shape, and any volume above the plane.
- Real projects must also consider height districts, shadow regulation, local ordinances, site level differences, and municipal interpretation.
Calculation Process
Editorial Explanation- Step 1
Identify north and the boundary
Mark north direction, the north-side neighboring boundary, and the relationship between the building and the northern neighbor.
- Step 2
Check applicable zoning
Confirm whether the site is in a residential zoning category where north-side slant is important, and identify the study starting height.
- Step 3
Measure distance and confirm slope
Measure the horizontal distance from the north boundary to the relevant building part, then identify the study slope.
- Step 4
Apply the formula
Use height limit = starting height + horizontal distance × slope, then check roofs, upper floors, and projections.
Worked Examples
ExampleBasic Example
Problem
Category I low-rise residential, 5m base
- Step 1True-north horizontal distance from the north-side boundary is 4m, slope 1.25.
- Step 2Height limit = 5m + 4m × 1.25 = 10m.
Answer
The exam point is the 5m base for low-rise residential study cases.
Exam Example
Problem
Category I mid/high-rise residential, 10m base
- Step 1True-north horizontal distance is 4m, slope 1.25.
- Step 2Height limit = 10m + 4m × 1.25 = 15m.
Answer
Exams often test the base-height difference between low-rise and mid/high-rise residential districts.
Applicability Check
Problem
Check zoning before using the formula
- Step 1North-side slant is commonly tested for low-rise residential districts, rural residential districts, and mid/high-rise residential districts.
Answer
If the problem gives another zoning category, do not apply the formula mechanically.
Direction Check
Problem
True north is not arbitrary top-of-page north
- Step 1The legal-study phrase is true-north horizontal distance, 真北方向の水平距離.
- Step 2Draw orientation first, then measure.
Answer
Do not assume the top of the diagram is north.
Examples
Example- Example 1: 第一種低層住居専用地域, starting height 5m, horizontal distance from the north boundary 4m, slope 1.25. Height limit = 5m + 4m × 1.25 = 10m. This is a study example, not a legal determination.
- Example 2: 第一種中高層住居専用地域, starting height 10m, horizontal distance 4m, slope 1.25. Height limit = 10m + 4m × 1.25 = 15m. Different starting height changes the envelope significantly.
- Example 3: a high volume close to the north boundary may require a roof cut; setting back the upper volume increases horizontal distance and can reduce the conflict.
- Example 4: a shadow-regulation problem should not be solved by the north-side slant formula alone. North-side slant is geometry; 日影規制（にちえいきせい） is time-based shadow impact.
Comparison Table
Editorial ExplanationRoad Slant vs North-side Slant
| Road Slant | North-side Slant | |
|---|---|---|
| Control side | Street side | North-side neighboring boundary |
| Main purpose | Street-side openness and pressure control | Daylight, ventilation, and residential environment of the northern neighbor |
| Design impact | Street facade, upper setback, street section | Roof shape, second/third-floor massing, northern setback |
North-side Slant vs Shadow Regulation
| North-side Slant | Shadow Regulation | |
|---|---|---|
| Method | Geometric slant plane | Shadow impact over specified times |
| Core variables | Starting height, horizontal distance, slope | Measurement plane, time period, shadow length |
| Common trap | Do not check total height only | Do not replace it with the north-side slant formula |
Exam Preparation
Exam Reference- Common exam point: Building Standards Act Article 56 paragraph 1 item 3. First check whether the zoning is one where north-side slant applies.
- Applicability keywords: 第一種低層住居専用地域, 第二種低層住居専用地域, 田園住居地域, 第一種中高層住居専用地域, 第二種中高層住居専用地域.
- Fill-in style keyword: true-north horizontal distance, 真北方向の水平距離. Do not reduce it to a generic distance.
- Numeric exam point: slope 1.25; low-rise residential and rural residential commonly add 5m, while mid/high-rise residential commonly adds 10m.
- Boundary reading: the true-north horizontal distance is read to the opposite road boundary line or neighboring boundary line depending on the problem condition. Identify the reference line first.
- Common trap: mixing north-side slant with road slant. Road slant does not use the 5m/10m starting height; north-side slant is not about street sky openness.
- Problem-solving order: check zoning → mark true north → locate the north-side/reference boundary → write starting height → multiply distance by 1.25 → check roof and upper volume.
Common Mistakes
Editorial Explanation- Assuming every zoning district has north-side slant restriction without checking applicability.
- Forgetting starting height and using only horizontal distance × slope.
- Confusing north-side slant with road slant: one protects the northern neighbor, the other protects the street side.
- Treating shadow regulation as the same as north-side slant.
- Checking only total building height instead of the horizontal distance from the north boundary to relevant parts.
- Ignoring roof shape, penthouse elements, upper projections, and second/third-floor massing.
Memory Tips
Exam Reference- North-side slant: first ask “is this an applicable residential district?”, then ask “5m base or 10m base?”
- Memorize the study formula as: starting height + true-north horizontal distance × 1.25.
- Low-rise residential and rural residential are commonly 5m; mid/high-rise residential is commonly 10m.
- Road slant looks at the road. North-side slant looks along true north toward the neighbor.
- 日影規制（にちえいきせい） is time-based shadow impact, not a renamed north-side slant formula.
Next Topic
Related Topics
Related Glossary
Related Code Topics
Further Reading
- Building Standards Act Article 56 paragraph 1 item 3
- e-Gov Building Standards Act
- MLIT group regulation materials
Official Source
北側斜線制限
建築基準法 第56条第1項第3号（要最終確認）
Official Source
北側斜線制限
建築基準法 第56条第1項第3号（要最終確認）
- Regulation
- 建築基準法
- Article Number
- 建築基準法 第56条第1項第3号（要最終確認）
- Note
- 北側斜線制限の根拠条文として扱う学習用参照。用途地域、起算高さ、適用条件は最終確認が必要。
- Verification State
- Draft
- Last Reviewed
- Not Reviewed
北側斜線制限
Guide reference
Government Guide
北側斜線制限
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。北側斜線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.