How is the area of Japanese houses calculated? What is the difference between 'exclusive area' and 'building area'?

Hey there! The way floor area is calculated for Japanese properties can indeed be confusing for those new to the market. Let me break it down for you in simple terms.

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Core Concept: What Area Are You Actually Buying?

When buying property in Japan, especially apartments (マンション), you'll most often hear two terms: "Exclusive Area" and "Building Footprint Area". Simply put:

• Exclusive Area (専有面積 - sen'yū menseki): This is the private space you actually pay for and own.
• Building Footprint Area (建築面積 - kenchiku menseki): This is mainly a technical term used during construction and isn't very relevant to your daily life as a resident.

Let's dive into these concepts in detail.

1. Exclusive Area (専有面積 - sen'yū menseki)

This is the area you need to care about most! It refers to the space within the apartment building that is entirely under your personal control and for your exclusive use.

• Simple Explanation: Think of it as the space "inside your front door". This includes your living room, bedrooms, kitchen, bathroom, and closets (wardrobes, storage areas).

• What's NOT Included?

  • Balcony (バルコニー): Balconies are NOT part of the exclusive area! Although for your exclusive use, legally they are considered "common areas" that the developer allows you to use freely. In case of fire, balconies serve as crucial escape routes, so they aren't considered your private property.
  • Hallways, Elevator Lobbies, Stairwells outside your door: These are obviously shared common areas and definitely not included.
  • Small Private Entrance Porch (ポーチ): Some units have a small private space just outside the front door; this is also not included.

An Important Detail: Two Ways to Calculate Exclusive Area

Be aware that the Exclusive Area itself has two calculation methods, crucial to distinguish when viewing properties:

1. Hekishin Area (壁芯面積 - Hekishin Menseki)

   • Calculation: Measured from the centerline of walls and pillars.
   • Characteristic: Includes half the thickness of the walls, so this number is larger.
   • Use: This is the area typically advertised in real estate listings, brochures, and promotional materials because it makes the space appear larger.

2. Uchinori Area (内法面積 - Uchinori Menseki)

   • Calculation: Measured only from the inner surface of the walls – the actual usable floor space where you could lay carpet.
   • Characteristic*: This number is smaller than the Hekishin area, but it's the most accurate representation of usable space.
   • Use: This is the area recorded on the property deed (real estate registry). Bank loans and tax calculations (like fixed asset tax) are also based on the Uchinori area.

Tip: Generally, the Uchinori area is about 5%~7% smaller than the Hekishin area. When viewing a property, if the brochure says 70㎡, keep in mind that the registered and usable area might only be around 65㎡.

2. Building Footprint Area (建築面積 - kenchiku menseki)

For apartment buyers, understanding this concept is useful, but you don't need to delve deep into it.

• Simple Explanation: Imagine a sunny day at noon, with the sun directly overhead. The area covered by the shadow cast by the entire building on the ground is roughly equivalent to the Building Footprint Area.

• What it Calculates: It calculates the maximum horizontal projection area of the entire building, including walls, pillars, and even parts of overhanging eaves.

• Primary Use: This is a regulatory concept used during construction. The government uses it to calculate the "Building Coverage Ratio (建ぺい率)" – the maximum percentage of a plot of land that can be covered by a building – to ensure adequate space and sunlight in urban areas.

In short: Building Footprint Area is for "building regulations", while Exclusive Area is for "buying/selling" and "living in" the property.

Summary: Key Differences at a Glance

Final Advice for Buyers

As an apartment buyer, you just need to remember these key points:

1. Focus on the "Exclusive Area" – this is the core space you are paying for.
2. Distinguish between "Hekishin Area" and "Uchinori Area". Advertised figures are usually "Hekishin" (makes it look larger), while the deed uses "Uchinori" (the real usable area). When comparing properties, use the same standard – ideally Uchinori – for a fair comparison.

Hope this explanation helps! When viewing properties in Japan, pay attention to which area is indicated on the floor plans, and you'll have a much clearer picture.