BHU Technical Terms Glossary: 12 Construction & Fire Safety Terms Explained
An assessment report or renovation quotation for BHU certification is full of construction shorthand — "FD30", "FRR-60", "Option B ventilation" — that most landlords have never had to decode. This glossary explains 12 construction and fire safety terms drawn directly from Schedule 1 of the Basic Housing Units Ordinance (Cap. 658), each with its statutory basis and what it means for your renovation budget. It complements our companion 22-term BHU legal and status glossary, which covers regulatory and identity terms rather than construction specifications.
- FD30 fire doors (30-minute rating) and FRR-60 partition walls (60-minute rating) are two separate fire-resistance requirements for two different building elements
- The toilet fixture trio — flush toilet, washbasin, and bathtub or shower — is mandatory under Schedule 1 s.5(2); a toilet missing the shower fixture fails even if it is otherwise enclosed and waterproofed
- Water and electricity meters must be issued directly by the Water Supplies Department and CLP Power / Hongkong Electric for that specific subdivided unit — an electrician-installed internal sub-meter does not comply
Source: Basic Housing Units Ordinance (Cap. 658), Schedule 1 · Housing Bureau BHU Code of Practice
1. Fire Safety Terms: Doors, Walls, Detectors, Extinguishers
Schedule 1, Section 3 of Cap. 658 requires a subdivided unit to prevent fire spread and provide sufficient escape routes. The following five terms appear most often in assessment reports and renovation quotations.
FD30 Fire Door
30-minute fire resistanceLegal basis (Schedule 1, s.3): A subdivided unit's design and partitioning must be capable of preventing fire from spreading within and outside the principal flat. In practice, this means the door at each unit's entrance to the common corridor must carry an FD30 (30-minute fire resistance) rating and have a functioning self-closing mechanism.
What it means for landlords: Timber, glass, or thin metal doors typically do not meet FD30 and must be replaced. A door propped open with a wedge fails inspection even if the door itself is rated. Supply and installation typically costs HKD 3,000–8,000 per door.
FRR-60 Partition Wall
Fire Resistance Rating · 60 minutesLegal basis (Schedule 1, s.3): The partition walls between subdivided units must have sufficient fire and smoke resistance. In practice, partition walls between units are typically required to achieve an FRR-60 (60-minute fire resistance) rating, preventing fire from spreading from one unit to an adjacent one.
What it means for landlords: Timber-board or aluminium partitions generally do not reach FRR-60 and are a common inspection failure. Unsealed gaps at ceiling voids also void the wall's fire rating and must be closed with fire-stopping materials.
Independent Fire Detector
Inspected every 12 monthsLegal basis (Schedule 1, s.3): Each subdivided unit, and the common parts of the principal flat, must each have sufficient independent fire detectors, inspected at least once every 12 months. Detectors inside units and in common parts are counted separately — a shared detector does not satisfy both requirements.
What it means for landlords: This is an ongoing obligation, not a one-off installation — annual inspections and retained records are required throughout the 60-month certification period.
Fire Extinguisher (Common Parts)
Inspected every 12 monthsLegal basis (Schedule 1, s.3): The common parts of the principal flat must have sufficient fire extinguishers, inspected at least once every 12 months. Cap. 658 does not mandate an extinguisher inside each individual subdivided unit.
What it means for landlords: Fire extinguishers go in the common corridor and are usually inspected together with fire detectors by the same contractor, keeping this item relatively low-cost.
FS251 Fire Service Installation Plan Application
FSD plan submissionPractical basis: FS251 is the Fire Services Department form number used to submit plans for fire service installations and equipment — such as fire alarm systems — during renovation works. It is a construction-process requirement, not a clause of Cap. 658 itself.
What it means for landlords: A single fire door swap rarely needs a separate submission, but larger fire-system alterations (e.g. adding a fire alarm system) may require an FS251 plan to be lodged with the FSD first. Build approval time into your renovation schedule if this applies.
2. Ventilation Terms: Option A vs Option B
Schedule 1, Section 7 sets out two parallel compliance routes. Understanding the specific technical thresholds of each is essential for judging which route your unit falls under.
Option A / Option B Ventilation
Natural vs MechanicalLegal basis (Schedule 1, s.7): Rooms (including kitchens, excluding the toilet) must satisfy either Option A (natural ventilation) — compliance with Regulations 30, 31, 32 and 33 of the Building (Planning) Regulations — or Option B (mechanical ventilation) — an openable window (see below), artificial lighting, and mechanical ventilation achieving at least 5 air changes per hour (5 ACH). The toilet has a parallel pair: Option A (Regulation 36) or Option B (artificial lighting + 5 ACH, no window required).
What it means for landlords: Either route satisfies the requirement — you don't need both. The most common failure is insufficient window area combined with no compliant mechanical system installed, meaning neither Option A nor B is met.
Openable Window & Glass Surface Area
≥ 0.1 sq mLegal basis (Schedule 1, s.7): Under Option B, a room must have at least one openable window with a glass surface area of at least 0.1 sq m, providing sufficient access to the outdoors.
What it means for landlords: This is a minimum threshold that applies alongside the mechanical system under Option B — a fully sealed, windowless room does not comply even with a functioning ventilation fan installed. The toilet is exempt from this window requirement.
3. Toilet and Utility Terms: Schedule 1 Sections 5, 6 and 8
The toilet is typically the single largest cost item in a BHU renovation. The following five terms clarify the specific fixtures required and the technical definition of independent metering.
Enclosed & Waterproofed Toilet
Schedule 1 s.5(1)Legal basis: A subdivided unit must have a toilet that is enclosed and waterproofed, for the exclusive use of its occupant.
What it means for landlords: "Enclosed" means a solid wall or partition — not a curtain or half-height divider. "Waterproofed" means a proper waterproof membrane in the floor and walls, not simply tiled surfaces. A shared bathroom serving multiple subdivided units, common in older-style layouts, must be converted to an exclusive one per unit.
The Toilet Fixture Trio
Flush toilet + washbasin + bathtub/showerLegal basis (Schedule 1, s.5(2)): The toilet must have (a) a flush toilet, (b) a washbasin, and (c) a bathtub or shower — all three, with no exceptions.
What it means for landlords: A common misconception is that "the toilet is already enclosed" equals compliance — but a toilet with only a flush toilet and washbasin, missing a shower fixture, still fails Schedule 1 s.5(2)(c) and needs a shower installed before it can pass.
Water Point & Sink Outside the Toilet
Schedule 1 s.6Legal basis: A subdivided unit must provide a water point and sink outside the toilet — usually for cooking or cleaning use — and the surrounding area must also be waterproofed.
What it means for landlords: This is a separate requirement from the toilet fixture trio: the toilet's flush toilet and washbasin fall under s.5, while the outside sink falls under s.6. In units without a separate kitchen, this outside water point often doubles as the cooking water source.
Proper Load-Bearing Capacity
Schedule 1 s.4Legal basis: A subdivided unit and its principal flat must not carry a load exceeding their respective proper load-bearing capacity.
What it means for landlords: This standard typically applies to units with a mezzanine, rooftop structure, or altered internal structure — the specified professional must assess whether new partitions or platforms exceed the building's original design load, sometimes requiring a separate structural assessment by a Registered Structural Engineer (RSE).
Dedicated Water & Electricity Meter
Schedule 1 s.8Legal basis: A subdivided unit must have (a) a water meter provided by the Water Supplies Department specifically for that unit, and (b) an electricity meter provided by Hongkong Electric or CLP Power specifically for that unit.
What it means for landlords: The key phrase is "provided specifically for that unit" — an electrician-installed internal sub-meter downstream of the flat's main meter does not comply. It must be a separate account meter issued directly by the utility company. A single shared meter with proportional bill-splitting is equally non-compliant.
Frequently Asked Questions
What's the difference between FD30 and FRR-60?
FD30 is a fire door rating, requiring the door from a unit to the common corridor to resist fire and smoke for at least 30 minutes. FRR-60 is a fire resistance rating (Fire Resistance Rating) for partition walls, requiring the wall between two subdivided units to resist fire for at least 60 minutes, preventing spread from one unit to an adjacent one. They apply to different building elements with different time thresholds, both derived from the fire safety requirements in Schedule 1, s.3.
Can I mix Option A and Option B ventilation in the same unit?
Different rooms can use different options, but each room must satisfy one option in full — you cannot partially meet Option A and partially meet Option B for the same room. If a room's window area already meets the natural ventilation standard under Regulations 30–33 (Option A), no mechanical system is needed. If window area is insufficient, all three Option B elements — openable window ≥0.1 sq m, artificial lighting, and 5 ACH mechanical ventilation — must be met together.
My toilet is already enclosed — why does it still fail?
The most common reason is a missing bathtub or shower. Schedule 1, s.5(2) requires a flush toilet, a washbasin, AND a bathtub or shower — all three, no exceptions. Many older-style enclosed toilets have only a flush toilet and washbasin, without any shower fixture. Even though the toilet is properly enclosed and waterproofed, it still fails the fixture-trio requirement and needs a shower installed before it can pass inspection.
Does an electrician-installed sub-meter count as an "independent electricity meter"?
No. Schedule 1, s.8 requires the electricity meter to be provided by CLP Power or Hongkong Electric "specifically for" that subdivided unit — meaning a separate account meter issued directly by the utility company, not an internal sub-meter added by an electrician downstream of the flat's main meter. The same principle applies to the water meter, which must be provided by the Water Supplies Department specifically for that unit. Owners must apply directly to the utility companies rather than relying on a contractor-installed sub-meter.
What is FS251 and is it needed for every renovation?
FS251 is the Fire Services Department form number for submitting plans for fire service installations and equipment, mainly used for larger-scale fire system changes such as adding or modifying a fire alarm system. A single fire door replacement usually doesn't need a separate FS251 submission, but when a renovation involves systematic changes to fire installations, contractors or specified professionals typically recommend confirming whether an FS251 submission is required — landlords should build approval time into their renovation schedule accordingly.