Opening a sauna or public bath (koshu yokujo): what does the property need to satisfy? — the Public Bath Houses Act and zoning

In short: for a sauna, public bath or spa, the first things that bite are (1) zoning — a public bath, other than one tied to the adult-entertainment "private-room bath" business, can be built across a wide range of zones, so this rarely blocks you; (2) the structural-equipment standards required by the Public Bath Houses Act, which are set by prefectural bylaw and differ by municipality; (3) the change-of-use confirmation application — a public bath is a "special building" under the Building Standards Act, so over 200 m² of that use it is generally required; and (4) drainage, ventilation and Legionella control. The real gate in choosing a property is not zoning but structure, change-of-use and fire safety. Check the bylaw and the completion certificate before signing, and you avoid rework.

You are told "the bathing fixtures from the last tenant are still here, so you can open straight away," you sign — and at the operating-permit stage both the public health centre and the building authority ask you to rebuild. The same rework that hits restaurant and clinic properties hits saunas and public baths too. This article is for operators opening a sauna, public bath or spa in Tokyo, and for those letting such property, and sets out what you can check before signing a lease or buying — from the Public Bath Houses Act, the Building Standards Act, the Fire Service Act and the Ministry of Health, Labour and Welfare's management guidance. Obtaining the operating permit itself is the administrative scrivener's field and is left to a separate article; here we focus on the property conditions seen from the real-estate side. The final check on feasibility is made at the building authority, the public health centre and the fire department.

Where can a sauna or public bath property be located under zoning?

The short answer: zoning rarely becomes the gate — that is what sets saunas and public baths apart from restaurants and hair salons.

Table 2 of the 建築基準法 (Building Standards Act, Act No. 201 of 1950) sets out what may be built in each zone. A public bath — "excluding one tied to the private-room bath business" — is listed among the buildings permitted even in the strictest Category 1 low-rise exclusive residential zone, and in every zone above it, because public baths have long been treated as facilities needed by the community.

Zone	Public bath (excluding adult-entertainment private-room baths)
Cat.1 / Cat.2 low-rise exclusive residential; rural residential	Permitted (an adult-entertainment private-room bath is not)
Mid/high-rise, residential, quasi-residential zones	Permitted
Neighbourhood commercial, commercial, quasi-industrial, industrial	Permitted
Exclusively industrial zone	Check the municipality's operation

The point to watch is the "public bath tied to the private-room bath business." That is defined under the Act on Control and Improvement of Amusement Business, and its zoning is heavily restricted. An ordinary sauna, public bath, super-sento or rock-bath is not the private-room bath business, but depending on the concept, the line should be checked.

So what you should clear first is not zoning but the structure, change-of-use and fire-safety points below. How zoning and floor-area ratio move land price is set out in Why Japanese land value changes with "floor-area ratio"; an example where fire and municipal checks come before the contract is in Conditions of a property where you can run a minpaku.

What structural and equipment requirements does the Public Bath Houses Act impose?

Running a public bath as a business needs the prefectural governor's permit. Article 2, paragraph 1 of the 公衆浴場法 (Public Bath Houses Act, Act No. 139 of 1948; last amended by Act No. 122 of 2011) provides that "a person who intends to operate a public bath as a business must obtain the permit of the prefectural governor." Article 1 defines a public bath as "a facility that uses hot water, sea-water baths, hot springs or the like to let the public bathe," and saunas, public baths and spas fall within it.

Whether the permit issues turns on the property's build. Article 2, paragraph 2 lets the governor withhold the permit where the location or the structural equipment is "unsuitable from a public-health standpoint," or where the location "lacks appropriateness of placement," and paragraph 3 has the prefecture set the placement standards and the structural-equipment standards by bylaw. Article 3 further requires measures for ventilation, lighting, illumination, heat retention, cleanliness and other public-health needs, again leaving the standards to bylaw.

So the specific figures — the size of the bathing and changing rooms, hot-water supply and washing places, ventilation capacity — are set by the bylaw of each prefecture (or, for cities and special wards with their own health centre, that city or ward), and differ by municipality. "It passed at this size in the next prefecture" does not carry over.

On the property side, rather than the bylaw figures themselves, check whether the groundwork to meet them exists.

Check before signing	Why it bites
Layout that can separate changing and bathing rooms by sex	Many bylaws require separation by sex, clear partition, and screening
Position and diameter of water/drainage; hot-water capacity	Tubs, showers and saunas need heavy hot-water supply and drainage
Ventilation and room to add it	Discharging heat and humidity depends on ventilation
Electrical / gas capacity	Sauna heaters, boilers and filtration circulation need capacity
Waterproofing and damp-proofing of floors and walls	Groundwork to withstand constant moisture; ties into reinstatement scope

Water, drainage, ventilation and electrical design are the contractor's (designer's) field. We — the real estate company — walk alongside you on the groundwork check of whether the property can meet these, and on negotiating terms with the landlord. We do not do the equipment design itself.

Note that public baths split into ordinary public baths (the traditional sento) and other public baths (saunas, super-sento, rock-baths, spas, etc.). Ordinary public baths often carry a placement standard (a distance rule) by bylaw keeping them apart from existing baths, and their bathing fees fall under the Price Control Ordinance. Other public baths generally carry no distance rule and set their own fees. A new sauna or spa is usually an "other public bath," so it is less likely to hit the placement standard, but the structural-equipment standards are still set separately by bylaw. Which one applies changes with the concept, so confirm it with the health centre at the outset.

For drainage, ventilation and Legionella control, what matters in choosing a property?

Saunas and public baths handle water, heat and humidity even more than restaurants do. That feeds straight into the property choice.

First, hot-water and drainage capacity. Tubs, showers and cold plunges use large volumes and discharge accordingly. Look — before signing, with the contractor — at the diameter of the incoming water/drainage pipes, where the storage tank and boiler go, and the drainage gradient and connection point.

Second, ventilation. Whether you can route heat and humidity outside (ducts, intake and exhaust), and whether the landlord permits penetrating the exterior wall or roof, is the same issue as a restaurant's exhaust duct. This structure is shared with In a skeleton property for a restaurant, how far do exhaust, grease traps and fire safety decide the choice.

Third, Legionella control. Recirculating tubs let Legionella breed in filters and pipes, and outbreaks of Legionnaires' disease at public baths have been a past problem. The Ministry of Health, Labour and Welfare's management guidance for hygiene at public baths sets out disinfection of bath water (chlorine, etc.), management of the recirculating filter, encouragement of "flow-through," and temperature management of the storage tank (accessed 16 September 2026). At the property stage, whether there is space for a plant room to house the circulation gear, and groundwork to keep the pipework short and simple, shapes how manageable hygiene will be later.

What to look at in the property	Where it bites
Location and capacity of hot-water supply / boiler	Simultaneous use of tubs, showers and sauna
Diameter, gradient and connection of drainage	Heavy discharge; handling grease and hair
Route for ventilation/exhaust and whether penetration is allowed	Discharge of heat and humidity; needs landlord consent
Plant-room space (circulation filter, storage)	Legionella control and ease of maintenance

The design and construction here are the contractor's, and the hygiene operation is the operator's. We walk alongside you on the groundwork check.

For a second-hand property, how do you check change-of-use and the completion certificate?

This is the gate peculiar to saunas and public baths. A public bath is a "special building" under the Building Standards Act (Table 1, column (i), item (4) lists "public bath").

So when you convert a second-hand office or shop into a sauna or public bath, if the floor area for that use exceeds 200 m², a change-of-use confirmation application is generally required. Article 87, paragraph 1 of the Building Standards Act applies the confirmation procedure where a use is changed to a special building under Article 6, paragraph 1, item 1 (a use in Table 1 column (i) over 200 m²). This contrasts with hair salons and clinics, which rarely trigger a change-of-use confirmation — miss it and the opening stalls.

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Together with this, check the completion certificate. A second-hand building without one can hit obstacles at the change-of-use confirmation or with bank financing. Even without it, a legal-compliance survey can sometimes confirm the building's lawfulness at the time of construction, and you need to tell an existing-nonconforming building from an illegal one. This point is set out in Can a second-hand property without a completion certificate be converted to a welfare facility.

Check in a second-hand property	Where / who	Why it bites
Whether the relevant-use area exceeds 200 m²	Drawings, building authority	If so, a change-of-use confirmation (Art. 87)
Presence of a completion certificate	Certificate; ledger extract	Whether a legal-compliance survey is needed if absent
Existing-nonconforming vs illegal building	Architect, building authority	Directly affects whether and at what cost it can be corrected
Current state of fire-safety equipment	Fire department, drawings	The equipment required differs between item (9)(a) and (b)

And fire safety. Table 1 of the Fire Service Act Enforcement Order classifies a sauna (a steam bath, hot-air bath or the like) as item (9)(a) and other public baths as item (9)(b). Because item (9)(a) handles fire and high heat, its fire-equipment and evacuation standards can be stricter than item (9)(b). Change-of-use and building confirmation are handled by an architect (designated confirmation and inspection body); fire consent and fire equipment by the fire department. The need for a change of use, the completion certificate and the fire equipment can all be checked at the building authority and fire department before signing. For business property generally, see Investment and business-use real estate; for the relation between an office and permits, Company set-up and choosing an office. Why the same rework hits care-service premises is in The real reason you cannot find premises for a care business; which parts of the lease to read is in The lease agreement — which parts to read.

Who should you ask for the permit, the building confirmation and fire safety?

Opening a sauna or public bath is a field with many specialists. Arranging them at the outset avoids confusion.

Task	Who
Property investigation, condition check, brokerage, sale/lease contract	四葉不動産株式会社 (licensed real estate agent)
Public-bath operating-permit application; documents for the health centre	Administrative scrivener
Design and application for change of use / building confirmation	Architect (designated confirmation and inspection body)
Fire consent, fire equipment, fire-object notification	Fire department, fire-equipment engineer
Design and construction of water, drainage, ventilation and filtration	Contractor

Property investigation, brokerage and the sale/lease contract are handled by Yotsuba Real Estate Co., Ltd. (四葉不動産株式会社; licensed real estate agent, Tokyo Governor (1) No. 113304). Preparation of documents for public authorities — the public-bath operating-permit application, for instance — is handled by 四葉行政書士事務所. These two (the real estate company and the administrative-scrivener office) are independent business entities, engaged separately and directly by you. We neither pay nor accept referral fees or introduction commissions. Change-of-use and building-confirmation design is for an architect, fire equipment for a fire-equipment engineer, registration for a judicial scrivener, and tax for a tax accountant — each engaged by you directly. Consultation is free of charge. The authorities' counters, forms, bylaw figures and intake practice change. At the outset, check the pages of the health centre, building authority and fire department having jurisdiction directly.

Frequently asked questions

Q. Can a sauna or super-sento open in a residential area (Category 1 low-rise exclusive residential zone)?
A. Table 2 of the Building Standards Act lists "public bath (excluding one tied to the private-room bath business)" among the buildings permitted even in a Category 1 low-rise exclusive residential zone. On zoning alone, there is room to open. But the Public Bath Houses Act's structural-equipment standards (prefectural bylaw), the change-of-use confirmation, fire safety and neighbourhood considerations bite separately. Zoning feasibility differs by property, so check at the building authority.

Q. If the property was a bath house before (a fit-out), will the operating permit pass as-is?
A. Not necessarily. The Public Bath Houses Act permit is granted per property and per operator; the previous shop's permit does not carry over, and bylaws or practice may have been revised. Inspect the state of the left-behind equipment (tubs, circulation filter, boiler), its compliance with the current bylaw, the Legionella-control build and the current fire equipment before handover, and confirm with the health centre and fire department.

Q. If I convert a room in an office building into a sauna, is a change-of-use confirmation needed?
A. A public bath is a special building under the Building Standards Act, so when the floor area for that use exceeds 200 m², a change-of-use confirmation is generally required (Article 87, paragraph 1). Even at 200 m² or under, zoning restrictions and the substantive rules on lighting, ventilation and fire safety still apply. The need turns on floor area, structure and zone, so confirm at the building authority before signing.

Q. Is a sauna treated differently from an ordinary public bath under the Fire Service Act?
A. Yes. Table 1 of the Fire Service Act Enforcement Order classifies a steam bath, hot-air bath or the like (a sauna) as item (9)(a), and other public baths as item (9)(b). Item (9)(a) handles fire and high heat, so its fire-equipment and evacuation standards can be stricter than item (9)(b). The equipment required also changes with the building's scale and number of storeys, so confirm with the fire department.

Sources (primary)

• e-Gov "公衆浴場法" (Public Bath Houses Act) — Act No. 139 of 1948. Art. 1 (definition of a public bath); Art. 2 (1) (governor's permit to operate as a business); (2) (permit may be withheld where location/structure is unsuitable for public health or placement lacks appropriateness); (3) (placement and structural-equipment standards set by prefectural bylaw); Art. 3 (ventilation, lighting, heat retention, cleanliness etc., standards delegated to bylaw). Last amended by Act No. 122 of 2011. Accessed 16 September 2026.
• e-Gov "建築基準法" (Building Standards Act) — Act No. 201 of 1950. Table 1, column (i), item (4) (public bath is a special building); Table 2 (buildings by zone — a public bath, excluding the private-room bath business, is buildable from the Cat.1 low-rise exclusive residential zone up); Art. 48 (zoning restrictions); Art. 6 (1) (i) (confirmation for special buildings over 200 m²); Art. 87 (1) (confirmation on change of use). Accessed 16 September 2026.
• e-Gov "消防法施行令" (Fire Service Act Enforcement Order) — Cabinet Order No. 37 of 1961. Table 1, item (9)(a) (steam bath, hot-air bath or the like) and (9)(b) (other public baths); fire-equipment standards vary with the classification of the fire object. Accessed 16 September 2026.
• Ministry of Health, Labour and Welfare, hygiene-management guidance for public baths — disinfection of bath water, management of the recirculating filter, storage-tank temperature and other Legionella-control thinking. Specific structural-equipment and hygiene figures are by the bylaw of each prefecture / health-centre city / special ward. Accessed 16 September 2026.

The specific figures for structure and hygiene (bathing and changing-room size, hot-water/washing/ventilation capacity) are set by the bylaw of each prefecture, health-centre city or special ward and differ by municipality; this article makes no assessment of any individual property. Confirm at the health centre, building authority and fire department having jurisdiction at the outset. Zoning feasibility and the need for a change-of-use confirmation vary with floor area, structure and zone; the final check is at the building authority. Whether a case is a "public bath tied to the private-room bath business" changes with the concept, and if so the zoning changes greatly. This article is general information and does not judge or guarantee the feasibility of any property or the acceptance of an operating permit. Property investigation, brokerage and sale/lease contracts are undertaken by 四葉不動産株式会社 (licensed real estate agent); operating-permit and other public-authority documents by 四葉行政書士事務所 — two independent business entities, engaged separately and directly. Change-of-use and building-confirmation design is by an architect and fire equipment by a fire-equipment engineer. We neither pay nor accept referral fees.

About the author

Joji Uramatsu — licensed real estate transaction specialist (Tokyo Governor registration No. 293544) and administrative scrivener (registration No. 25087022). Representative Director, 四葉不動産株式会社 (Yotsuba Real Estate Co., Ltd.; real estate business licence: Tokyo Governor (1) No. 113304); Representative, 四葉行政書士事務所. Kohinata, Bunkyo, Tokyo, about five minutes' walk from Myogadani station. Property (real estate) and permits (administrative procedure) go on the same table. Full profile: author page.