Can I freely renovate or remodel my house? What are the restrictions?

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Regarding the question of whether you can freely renovate or remodel a house in Japan, let me break it down for you.

It really depends on the situation, and the key factor is whether you bought a detached house (ikkodate) or a condominium apartment (mansion). The rules for these two are a world of difference.

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If you bought a Detached House (Ikkodate)

Congrats! You have relatively high freedom. It's basically your land, your rules. However, this "freedom" still operates within a legal framework; you can't just tear down or build whatever you want.

Main Restrictions Come from the Building Standards Act

This is Japan's fundamental law governing construction, primarily ensuring the safety of your house and your neighbors' houses – that they won't collapse easily and won't spread fire uncontrollably. There are key hard limits you can't ignore:

1. Building Coverage Ratio (Kenpeiritsu)

   • Simply put: The ratio of your building's footprint area to your total land area.
   • Example: If your land is 100 sqm and the local coverage ratio is 60%, the maximum area your house's foundation (the shadow area looking down) can cover is 60 sqm. You can't cover the entire yard with the house; you must leave open space for sunlight, ventilation, and fire prevention.

2. Floor Area Ratio (Yōsekiritsu)

   • Simply put: The ratio of the total floor area of all your building's stories combined to your total land area.
   • Example: For the same 100 sqm land with a 150% floor area ratio, the combined area of all your floors (e.g., first floor + second floor) cannot exceed 150 sqm. This controls building density and height in the area, preventing everyone from building skyscrapers.

What kind of renovations require permission?

Depending on the scale of the renovation, it's divided into "requires application" and "basically doesn't require application".

• Major projects requiring submission of a Building Confirmation Application to the government:

  • Adding on: E.g., adding another story, or building a new garage or shed in the yard exceeding 10 sqm.
  • Large-scale remodeling/repair: E.g., demolishing and rebuilding more than half of the walls, pillars, beams, or other major structural components.
  • Changing the building structure: E.g., changing from a wooden structure to a steel structure.
  • Changing the building's use: E.g., converting a residence into a shop or office.

  In short: If you're touching the "bones" (structure) or significantly changing the "body" (size/volume) of the house, you generally need permission. This application process is professional and usually requires hiring an architect.

• Minor renovations that generally don't require permission:

  • Interior redecorating like painting walls, changing wallpaper, replacing flooring.
  • Replacing kitchen units, toilets, and bathtubs (as long as major pipe locations aren't changed).
  • Repainting the exterior walls.
  • Fixing roof leaks, etc.

  In short: "Internal beautification" that doesn't affect structural safety or change the area/height is generally free.

Important Note: Some areas, like historical preservation districts (Landscape Districts) in Kyoto, have special regulations for exterior wall color, materials, and even roof shape. It's best to check with the local city office before renovating.

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If you bought a Condominium Apartment (Mansion)

The restrictions here are much greater. The key point is that you've bought only the space inside a "concrete box," not the entire building. So, it's crucial to strictly distinguish between two concepts:

• Exclusive Use Areas (Sen'yū bubun): This is the part you truly own and can decide about.
• Common Areas (Kyōyō bubun): This is owned collectively by all owners and is strictly off-limits to you.

What is "Exclusive Use"? What is "Common Area"?

• Exclusive Use Areas (Places you can modify):

  • Think of it as the space inside your walls, floor, and ceiling.
  • E.g.: Interior wallpaper, carpets, flooring materials, internal non-load-bearing partition walls, kitchen fixtures, bathroom fixtures.

• Common Areas (Places you absolutely cannot touch):

  • Building Structure: Load-bearing walls, pillars, beams, floor slabs (the concrete layer between your floor and the ceiling below). You absolutely cannot make openings in or remove load-bearing walls.
  • Windows and Entrance Doors: Window frames, window glass, balcony doors, and your main entrance door are common areas! This is to maintain the building's uniform appearance, airtightness, and fire safety. You can decorate the interior side of doors and windows (e.g., paint), but you cannot change their style or color.
  • Balcony: The balcony is a common area, often designated as an emergency escape route in case of fire. Therefore, you cannot build storage sheds on it, enclose it, or pile up large amounts of clutter blocking the path.
  • Main Pipes in Shafts: Gas pipes, water pipes, sewage pipes, etc., that connect vertically.

The "Apartment Constitution" You Must Obey Before Renovating – The Management Regulations (Kanri Kiyaku)

Every condominium building has its own Management Regulations (Kanri Kiyaku), the supreme rules all owners must follow. Before planning any renovation, the very first thing is to find this document and read it thoroughly!

It typically details:

• Flooring Materials: This is the most common restriction. To prevent noise affecting downstairs neighbors, regulations usually specify the required sound insulation level for flooring (e.g., must use LL-45 or higher grade soundproof flooring). If you want to change from carpet to wood flooring, it must meet this standard.
• Renovation Application Process: Any renovation, even just changing flooring, usually requires submitting an application, renovation plans, and a list of materials to the Management Association (Kanri Kumiai, equivalent to the HOA/Residents' Committee) in advance and obtaining approval before starting work.
• Construction Hours: Typically, work is only allowed on weekdays during daytime hours; weekends and holidays are prohibited to avoid disturbing neighbors.
• Other Restrictions: E.g., whether moving the kitchen or bathroom location is allowed (as it involves altering drain pipes), whether gas stoves are permitted, etc.

The typical renovation process is: Have an idea -> Get a plan from a contractor -> Submit application to Management Association -> Obtain approval -> (Notify neighbors before starting) -> Begin construction

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To Summarize

In conclusion, the most important thing before renovating is to "confirm the rules." If you buy a detached house, confirm the laws and regulations; if you buy a condo, confirm the management regulations. Never just roll up your sleeves and start working based on assumptions. Otherwise, you might not only face neighbor complaints but could also be ordered by the management association or government to restore the property to its original state, which would be counterproductive.