Which Subdivided Flats
Cannot Be BHU Certified?
Not every subdivided flat can obtain BHU certification. Some units have structural constraints that no renovation can resolve. Understanding the ineligibility criteria before paying for an assessment can save both time and money.
- Floor area permanently below 8 sq m — total internal floor area (bathroom included) cannot be expanded
- Clear ceiling below 2.3m — at any point, due to structural beams or columns that cannot be removed
- No ventilation route achievable — fully enclosed room with no access to any outdoor air pathway
- Non-residential building — industrial or commercial buildings are outside the ordinance's scope
- Public housing / non-deed-restricted HOS — deed-restricted HOS is exempt; deeds-lifted HOS units are covered by the BHU scheme
- Unresolved unauthorised structures — must be declared and dealt with before certification can proceed
Source: Buildings Department BHU Code of Practice · Landlord and Tenant (Consolidation) (Amendment) Ordinance 2025
Floor Area and Ceiling Height: The Hard Thresholds
According to the BHU Code of Practice, each subdivided unit must have a total internal floor area of at least 8 sq m. This area is measured from the inner surfaces of the enclosing partitions and includes the bathroom. If a unit's total internal floor area is structurally limited to 6–7.5 sq m with no means of expansion, it cannot be certified as an independent BHU.
However, area shortfall is not always insurmountable. Two approaches may resolve it:
- Merge adjacent units: Combine two undersized adjacent rooms into one compliant unit. Fewer units means fewer tenants, but the rent for each larger unit typically rises accordingly — total rental income may not drop significantly.
- Reposition partition walls: If a wall is non-load-bearing, shifting its position to expand one room's habitable area may achieve compliance. Structural assessment by an Authorized Person is required before any works are carried out.
⚠️ Ceiling height: the most overlooked threshold
The BHU Code of Practice sets two separate ceiling height standards: the clear height from floor to ceiling surface must be at least 2.3m, while the clear height from floor to the underside of any beam must be at least 2.0m. False ceilings and AC pipework that reduce the ceiling surface below 2.3m are the most common failure point — removal can restore compliance. In one Owl Square Group assessment, the overall ceiling was 2.5m but false ceiling and AC pipework reduced the lowest ceiling surface to 2.15m, failing the 2.3m ceiling standard.
Unit Types Most Likely to Fail Dimensional Standards
Based on Owl Square Group's on-site assessment records, the following unit types most commonly fail area or height requirements:
- Pre-1980 tenement building subdivisions — habitable areas of 6–7.5 sq m are common
- Former storage rooms or domestic helper quarters converted into independent units
- Overly subdivided floors (e.g., 500 sq ft divided into 5 rooms)
- Rooftop additions and mezzanines with sloped structures
Ventilation: When Neither Option A Nor Option B Can Be Achieved
The BHU Code of Practice provides two ventilation routes: Option A (natural ventilation meeting Buildings (Planning) Regulations) and Option B (substitute: at least one openable window with glass area ≥ 0.1 sq m, plus mechanical ventilation at ≥ 5 air changes per hour). Most units with at least one window can comply via Option B — but the following situations make any ventilation route impossible:
- A room completely surrounded by other tenancies on all sides — no external wall, courtyard, or light well accessible whatsoever
- A window opening only into a fully enclosed, capped-over rooftop space — no longer a qualifying outdoor air pathway under the Code of Practice
- A window facing into another tenancy's private interior (not a public corridor or light well)
⚠️ Real Case: The Innermost Room
A 500 sq ft flat subdivided into 5 rooms had one room at the end of an internal corridor, completely enclosed on all sides by adjacent units — no street, courtyard, or light well was accessible. With both Option A and Option B impossible, the only solution was to absorb that room into an adjacent unit, reducing the layout to 4 rooms to achieve full ventilation compliance.
Building Use: Non-Residential Buildings Are Outside the Scheme
The BHU Ordinance applies only to the following building types:
- Private residential buildings (domestic buildings)
- Residential portions of composite-use buildings
Subdivided units in the following building types are not covered by the BHU Ordinance:
- Industrial buildings
- Commercial buildings (non-residential)
- Public rental housing (PRH)
- Home Ownership Scheme (HOS) units
- Private residential blocks
- Tong lau / old tenement buildings
- Composite-use building residential floors
- Village houses (certain situations)
⚠️ Outside BHU scheme ≠ legally compliant to rent
A unit in an industrial building not covered by the BHU Ordinance may still violate Buildings Ordinance use restrictions. Residential occupation of industrial premises carries its own legal risks. Being outside the BHU scheme provides no legal shelter for non-residential-building residential lettings.
Rooftop Structures: Categorically Excluded from the BHU Scheme
Rooftop additions (天台屋) are explicitly excluded from the BHU Ordinance. Under clause 3.2 of the BHU Code of Practice, structures erected in contravention of the Buildings Ordinance on rooftops, platforms, rear lanes, light wells, or courtyards are classified as non-applicable premises — they are outside the scheme and cannot apply for BHU certification.
⚠️ Rooftop additions: not "fix first, certify later"
The situation for rooftop additions is fundamentally different from standard subdivided flats. No amount of renovation brings a rooftop unauthorised structure within the BHU scheme — it is categorically outside it. Landlords must deal with rooftop structures under the Buildings Ordinance (notification, demolition, or regularisation), not via the BHU certification route.
If a property has both compliant floor-level subdivided units and a rooftop addition, the two must be handled separately. The floor-level units can proceed with BHU certification normally; the rooftop structure must be addressed under the Buildings Ordinance, and doing so does not affect the certification of the floor-level units.
Frequently Asked Questions
Which subdivided flats are definitively ineligible for BHU certification?
According to the BHU Code of Practice, the following are ineligible: total internal floor area (bathroom included) permanently below 8 sq m with no viable expansion; ceiling height below 2.3m (with a separate 2.0m minimum for beam undersides); no ventilation route achievable; units in industrial or commercial buildings; public housing and deed-restricted HOS units (deeds-lifted HOS is covered); and rooftop and platform unauthorised structures, which are categorically excluded from the scheme.
If my unit is below 8 sq m, is there any path to BHU certification?
Yes, potentially. Two approaches may resolve a floor area shortfall: merging adjacent undersized units into one compliant unit; or repositioning a non-load-bearing partition wall to expand the total internal floor area. Note that the 8 sq m minimum applies to the total internal floor area including the bathroom — it is not a bathroom-excluded habitable space measurement. If the total floor area still cannot reach 8 sq m after works, the unit cannot be certified as an independent BHU.
Can rooftop additions (天台屋) or mezzanines get BHU certified?
Under clause 3.2 of the BHU Code of Practice, rooftop additions and other structures erected in contravention of the Buildings Ordinance are classified as non-applicable premises — they are categorically outside the BHU scheme and cannot apply for certification. Landlords must address rooftop structures under the Buildings Ordinance, not via the BHU route. Floor-level subdivided units in the same property can still apply for BHU certification separately.
Are subdivided units in industrial buildings subject to BHU regulation?
No. The BHU Ordinance covers only private residential buildings and the residential portions of composite-use buildings. Industrial buildings are excluded. However, residential use of industrial premises may still violate Buildings Ordinance use restrictions — being outside the BHU scheme does not mean the tenancy is legally in the clear.
Do owner-occupied subdivided rooms require BHU certification?
No. The BHU Ordinance only applies to subdivided units used for rental purposes. Owner-occupied spaces are exempt. If part of a unit is owner-occupied and part is rented to tenants, only the rented rooms need to comply with BHU certification requirements.