BHU Certification for Old Buildings:
Mandatory Works Checklist
- Pre-1980 buildings almost always need fire-rated doors (per BHU CoP) and mechanical ventilation for windowless bathrooms (≥ 5 ACH) — budget HKD 18,000–33,000 per unit for a typical tong lau renovation
- Building age alone does not disqualify a unit; floor area (≥ 8 sq m) and ceiling height (≥ 2.3 m) are the harder barriers for old stock
- With the March 2027 enforcement deadline, allow 6–12 months for old building certification — book an AP assessment now
Pre-1980 Hong Kong buildings — tenements (唐樓, tong lau), pre-war buildings and seven-storey walk-ups — were not designed to modern fire separation or habitability standards. Landlords with subdivided units in these buildings typically face more extensive renovation requirements than those with newer stock. According to the Buildings Department's Code of Practice for BHU, the same technical standards apply regardless of building age — what changes is how much work is needed to reach them.
Old Building BHU Renovation: Works Overview
| Work Item | Necessity | Estimated Cost |
|---|---|---|
| Fire door (fire-rated per CoP) | Almost always | HKD 4,000–8,000 / unit |
| Mechanical ventilation | Required for windowless WC | HKD 3,000–6,000 / system |
| Independent electricity meter | Commonly required | HKD 2,000–4,000 / unit |
| Fire-rated partition walls (FRR-60) | Depends on materials | HKD 8,000–20,000 |
| Structural safety assessment | Pre-war buildings | HKD 3,000–8,000 |
Cost ranges based on Owl Square Group 2025–2026 assessment records. Actual costs depend on scope and contractor quotations.
Four Specific Challenges Old Buildings Face
According to the Buildings Department's BHU certification requirements, pre-1980 buildings systematically fall short in four areas:
Inadequate fire separation
Old building partitions are typically constructed from brick, timber or aluminium — not all of which meet the 60-minute fire resistance rating (FRR-60) required by the BHU Code of Practice for partition walls. Unit entrance doors almost never meet the fire resistance requirements specified in the CoP, making them the most commonly cited non-compliance item.
No mechanical ventilation
According to the BHU Code of Practice, windowless bathrooms must be served by mechanical ventilation achieving at least 5 air changes per hour (5 ACH). Habitable rooms must have openable windows facing the exterior with an aggregate openable area of not less than one-tenth of the room's floor area. Old building bathrooms are almost universally windowless and have no mechanical ventilation — both conditions require remediation.
Shared utility metering
Pre-1980 subdivided flats commonly share a single electricity meter across multiple units — a practice the BHU ordinance prohibits. Each certified unit must be independently metered for electricity; in some cases, independent water metering is also required.
Marginal floor area and ceiling height
Old building subdivided flats often have internal floor areas of just 6–7.5 sq m — below or dangerously close to the 8 sq m minimum. Beam soffits frequently bring ceiling heights below the 2.3 m threshold. Unlike fire doors or ventilation, these two issues have no simple remedy.
Mandatory Works: Item by Item
1. Fire door (BHU Code of Practice requirement)
According to the BHU Code of Practice, each unit entrance must be fitted with a fire door meeting the specified fire resistance requirements. Existing timber or hollow-core doors in old buildings universally fail this requirement.
- The door must include a self-closing mechanism (door closer or spring hinge)
- Fire-rated intumescent strips must seal the gap between door and frame
- Floor gap must not exceed 3 mm
- Supplier must provide an HKFSD-approved test certificate for the door assembly
⚠️ Common mistake
Some landlords replace doors with timber doors marketed as "fire-resistant" without obtaining the required test certificate or using a qualified contractor. The Buildings Department requires documentary evidence of door specification compliance — doors without certification will be rejected on assessment.
2. Mechanical ventilation
According to the BHU Code of Practice, windowless bathrooms must be served by a mechanical exhaust system achieving at least 5 air changes per hour (5 ACH). Living spaces without adequate natural ventilation must also be supplemented.
- Fan airflow (CMH) must equal bathroom volume × 5 — a 2 m³ bathroom needs at least 10 CMH
- Exhaust must discharge to the external atmosphere — discharge into common corridors is not acceptable
- Old buildings with limited duct routing may require custom engineering solutions, increasing cost
3. Independent electricity metering
Each BHU unit must be independently metered for electricity. The ordinance prohibits "shared meter" arrangements where multiple units run off a single account. Landlords must apply to CLP or HK Electric for sub-metering, or engage a qualified electrical contractor to install compliant sub-meters.
⚠️ Real case
A 1960s tong lau in Kowloon City with 4 subdivided units sharing a single meter required sub-meters plus rewiring for each unit. Total electrical works cost HKD 18,000 — an expense the landlord had not budgeted for before the AP assessment.
4. Fire-rated partition walls (where required)
Partition walls between units must achieve 60-minute fire resistance (FRR-60). Brick walls in old buildings typically meet this standard. Timber board, aluminium or light steel partitions do not — these require either demolition and rebuilding in suitable materials, or the addition of fire-rated lining boards.
5. Additional works that may be required
- Concrete spalling repair: Pre-war and 1950s–60s buildings commonly have concrete spalling on external walls or ceilings — a structural safety issue the AP must document in the assessment report.
- Drainage pipe replacement: Some old buildings still have severely corroded cast-iron or lead pipes, which must be replaced.
- Unauthorised structure removal: If any part of the unit involves a rooftop structure or other unauthorised addition, the Buildings Department may require removal before certification can proceed.
Cost Estimates: Two Typical Old Building Scenarios
Brick partitions already in place, natural ventilation in bathroom, independent meter already installed
| Fire door installation | HKD 4,000–6,000 |
| Minor sealing works | HKD 2,000–4,000 |
| Estimated renovation total | approx. HKD 6,000–10,000 |
Timber partitions, windowless bathroom, shared meter, multiple works required
| Fire door (per unit) | HKD 5,000–8,000 |
| Mechanical ventilation (per system) | HKD 3,000–6,000 |
| Independent electricity meter (per unit) | HKD 2,000–4,000 |
| Partial partition wall works | HKD 8,000–15,000 |
| Estimated renovation total | approx. HKD 18,000–33,000 |
These figures exclude the AP assessment fee (typically HKD 3,000–8,000) and Buildings Department filing fees. For a complete cost picture, see BHU Compliance Renovation Cost Guide 2026.
Pre-Assessment Checklist for Old Building Landlords
Use this checklist to identify likely issues before engaging an AP. Items flagged here will almost certainly require attention:
Any uncertainty on these points justifies arranging an AP assessment. An initial assessment (typically HKD 3,000–5,000) costs far less than discovering compliance gaps after renovation has already begun.
Frequently Asked Questions
Can subdivided units in old Hong Kong buildings (pre-1980) be BHU certified?
Yes — building age alone does not disqualify a unit. Whether a pre-1980 subdivided flat can be certified depends on its actual physical condition. Many tong lau units can be certified after renovation works; others fail due to insufficient floor area (below 8 sq m), low ceiling height (below 2.3 m), or structural problems. An on-site assessment by an Authorized Person is the only reliable way to determine eligibility.
What renovation works do old buildings typically need for BHU certification?
According to Owl Square Group assessment records, old building subdivided units most commonly require: fire-rated doors per BHU Code of Practice requirements, mechanical ventilation for windowless bathrooms (minimum 5 ACH), independent electricity sub-meters per unit, and fire-rated partition walls between units (FRR-60). Pre-war buildings may additionally need concrete spalling repairs or structural safety assessments.
What are the fire door requirements for BHU certification?
According to the BHU Code of Practice, each unit entrance must have a fire door meeting the specified fire resistance requirements, with a self-closing mechanism, fire-rated intumescent seals around the frame, and a maximum 3 mm floor gap. The supplier must provide a test certificate from an accredited laboratory confirming compliance with the required fire resistance rating.
How much does BHU renovation cost for an old building unit?
A well-maintained old building unit needing mainly a fire door: approximately HKD 6,000–10,000 per unit. A typical tong lau requiring fire doors, mechanical ventilation, independent meters and partition works: approximately HKD 18,000–33,000 per unit. These figures exclude AP assessment fees (HKD 3,000–8,000) and Buildings Department filing fees.
When should old building landlords start the BHU certification process?
Immediately. Renovation works for old buildings typically take 3–6 months, plus AP assessment and Buildings Department review time — the full process takes at minimum 6–12 months. With the 1 March 2027 enforcement deadline approaching, landlords should arrange an initial assessment now to confirm the scope of works required and begin planning.