Building Area / Eave Design Guide

7-2. Guide to Building Area Calculation of Truck Berth Eaves and the 5m Relaxation Exception

1. Basic Principle Where Eaves Are Included in "Building Area" (1m Rule)

Under the Building Standards Act, when a deep eave is installed at a truck berth to prevent load collapse during rain and improve work efficiency, the eave is treated as follows depending on its protrusion distance from the center line of the outer wall or pillars.

• Portion within 1m from the tip: Not included in the building area (excluded).
• Portion exceeding 1m: Everything exceeding 1m is included in the building area.
  • (Example: For an eave protruding 6m from the outer wall, the "5m portion" excluding the 1m tip is counted as building area, significantly squeezing the building coverage ratio.)
• If pillars are installed: If a pillar is erected to support the tip of the eave, the entire area surrounded by the center line of that pillar becomes "building area," and the 1m exclusion rule itself can no longer be used.

2. [Exception] Requirements for Building Area Relaxation for Large-Scale Eaves (5m Rule)

To promote logistics efficiency, an amendment to the Order for Enforcement of the Building Standards Act (provisions of Article 2, Paragraph 1, Item 5) was enacted, introducing a relaxation measure that excludes up to "a maximum of 5m" from the tip of the eave from the building area for logistics warehouses and factories meeting certain requirements.

2.1 Mandatory Requirements to Receive the 5m Relaxation

1. Use Restriction: The eave must be installed "exclusively for the purpose of loading and unloading freight" in a factory or warehouse.
2. No Room Above: No upper floor (room or work space) may be provided above the eave (*Areas for outdoor AC units or emergency access entrances are permitted).
3. Use of Non-Combustible Materials: The entire eave must be made of non-combustible materials.
4. Distance from Site Boundary Line:
   • The shortest distance from the tip of the eave to the site boundary line must be at least 5m apart.
   • The height of the eave must be less than or equal to the horizontal distance to the site boundary line (height restriction).
5. Area Upper Limit: The area of the eave that can be excluded must be 1/10 or less of the "buildable area" (Site Area × Designated Building Coverage Ratio) calculated for the entire site.

💡 Note: This 5m relaxation only applies to the "calculation of building coverage ratio (building area)." In judgments for road slant line restrictions or adjacent site slant line restrictions, it may still be calculated with the conventional 1m tip exclusion, so confirmation during layout planning is necessary.

3. Countermeasures/Design Techniques to Avoid Inclusion When Creating Deep Eaves

These are the main design methods to secure the effective depth (dry area) while avoiding exceeding the upper limit of the building coverage ratio.

• Cantilever (Overhang) Structure Fully Utilizing the "5m Relaxation": Adopting an "overhang structure" that protrudes from the main building with steel trusses, etc., without dropping pillars, and excluding the 5m tip, efficiently securing a practical 5m to 6m class eave.
• "Inset Berth (Piloti Style)" That Indents the 1st Floor of the Building: A method of placing the berth by recessing the 1st-floor outer wall of the main building inward, rather than protruding an eave outward. Because the floor of the upper story serves as the eave, it is not considered a protrusion from the outer wall, making it easier to plan the building coverage ratio.
• Utilization of Awnings (Movable Tents) / Retractable Membrane Structures: Rather than a fixed structure, adopting a "movable awning" that extends electrically only during unloading, or a lightweight "canvas eave (membrane structure)" that meets structural standards, and consulting/confirming its handling under building confirmation applications.
• Treating it as an Independent "Separate Roof (Shade)" and Using Garage Relaxation: Creating a canopy structure (roof + pillars) completely separated from the building, and upon meeting certain openness criteria, applying the volume/coverage ratio relaxation provisions for "garages/unloading areas" under a separate framework.

4. Simulation and Calculation Method When Applying the 5m Relaxation Exception

This is the procedure and calculation simulation method for calculating the maximum area of an eave that does not need to be included in the building area when applying the 5m relaxation exception (provisions of Article 2, Paragraph 1, Item 5 of the Order for Enforcement of the Building Standards Act).

4.1 Basic Calculation Rules and 3 Upper Limit Conditions

The area of the eave that can be "excluded from the building area" by applying the 5m relaxation exception is determined by whichever is the smallest (strictest) value among the following three conditions.

1. 5m Tip Rule (Dimensional Upper Limit): An area extending up to 5m maximum from the tip of the eave toward the outer wall (*Not just the 1m tip, but up to a maximum of 5m can be completely excluded).
2. Upper Limit of Building Coverage Ratio Quota (1/10 Rule): 1/10 (10%) of the "maximum buildable area" based on the designated building coverage ratio of the entire site.
3. Height/Separation Conditions (Site Boundary Restriction): Portions where the distance from the tip of the eave to the site boundary line is less than 5m are excluded from the 5m relaxation (reverting to the normal rule of excluding the 1m tip).

4.2 Calculation Steps

4.3 Specific Simulation Example

[Setting Conditions]

4.4 "Pitfalls" to Watch Out For

• Invalidated if Pillars are Dropped: If even a single pillar is installed at the tip or in the middle of the eave, it falls outside the application of the "5m relaxation," and the entire area enclosed by the pillars is added to the building area.
• Usage Restrictions for Upper Floors: If the upper part of the eave is used as a "room/warehouse where people work" other than a balcony or outdoor AC unit area, it is considered the "main building" rather than an eave, and the 5m relaxation can no longer be used.