Example: Building an Annex Extension

Example: an Annex Extension

(In the case of an annex extension to a residence with a total floor area of 100㎡ or less and two floors or less in a semi-fire prevention zone)

As a general rule, when building an separate annex, it is required to conform to the existing regulations. If it is an extension of an existing building, the collective regulations for the existing part and the individual regulations for structure, fire prevention, and evacuation are also applied retroactively. 
If a separate annex building is constructed,  some of the individual and collective regulations are not applied retroactively to the existing building. For details, please refer to the notes below. 

Collective Regulations:

• The building-to-land ratio and floor-area ratio shall be applied by taking into account the area of extension.
• The height regulations (road diagonal, neighboring land diagonal, north diagonal, altitude zone) are not applied retroactively to existing buildings.
• An annex can be built on a site facing a law-designated road for 2 meters or more or with a special permit.
• If the existing building extends into a road, the part of the building within the road must be removed.
• The provisions for installing fire prevention equipment at openings in the exterior walls of existing buildings are not applied retroactively. 

⇒ The provisions for fire prevention equipment for the area, height, and openings in the exterior walls are not applied retroactively. 

Individual Regulations (Existing Buildings) 
The individual regulations (provisions of Chapter 2 of the Building Standards Law) are not applied retroactively. 
The part of the building that was legal must remain legal after the expansion. 
⇒ The individual regulations are not applied retroactively. 

Procedural Regulations 

• In principle, applications for a building permit and for completion inspection are required. 
• ​In some cases, an application for interim inspection may be required depending on the building to be extended.
• ​In areas other than fire prevention and quasi-fire prevention areas, an application for building certification is not required for extensions with a floor area of 10 ㎡ or less.  
• It is necessary to comply with the Building Standard Law even if no application for building permit is required. 

Individual Regulations (Separate Building Extensions) 

• The current regulations are applied. 

Notes:
Conditions for Separate Annex Buildings (All of the following must be satisfied.) 
1. The buildings must be structurally separate. (Each building is independent in terms of structural durability. )
2. The buildings must be functionally separate. (The annex and the main building are not connected by an indoor space.)
3 The buildings must be separate in appearance. (The exterior of the buildings can be recognized as two buildings by socially accepted standards.)