Approved Document F (AD F) forms part of the UK Building Regulations, providing statutory guidance for achieving compliance with ventilation requirements in buildings. It ensures adequate indoor air quality, moisture control, and pollutant removal to safeguard occupant health and building integrity.
AD F is split into two volumes:
- Volume 1: Dwellings (houses, flats, and residential units).
- Volume 2: Buildings other than dwellings (offices, schools, hospitals, etc.).
The 2021 edition (effective June 2022) reflects updated standards for energy efficiency, health, and safety, including post-Grenfell reforms.
Purpose
To mitigate risks associated with poor ventilation:
- Health protection: Reduces condensation, mould growth, and exposure to pollutants (e.g., CO₂, VOCs).
- Building durability: Prevents moisture damage to structures.
- Compliance: Meets legal obligations under the Building Act 1984.
Key Requirements
For Dwellings (Volume 1):
- Extract Ventilation:
- Minimum rates for wet rooms (e.g., 30 l/s for kitchens, 15 l/s for bathrooms).
- Systems: Intermittent (manual) or continuous (mechanical).
- Whole-Dwelling Ventilation:
- Background ventilators (e.g., trickle vents) or mechanical supply.
- Minimum rates: 0.3 l/s per m² floor area or bedroom-based calculations (e.g., 19 l/s for 1-bed homes).
- Purge Ventilation:
- Rapid air exchange via openable windows (e.g., 1/20th floor area for hinged windows).
- Noise Control: ≤30 dB(A) in bedrooms, ≤45 dB(A) in kitchens.
For Non-Dwellings (Volume 2):
- Offices: 10 l/s per person or 1 l/s per m² (whichever is higher).
- Car Parks: CO limits (30 ppm average over 8 hours; 90 ppm peak).
- Indoor Air Quality Monitoring: Mandatory CO₂ sensors in occupiable rooms (e.g., gyms, classrooms).
Application Scope
- New builds, extensions, and material changes of use (e.g., office-to-flat conversions).
- Exemptions: Agricultural buildings, temporary structures, certain storage spaces.
- Historic Buildings: Flexibility for vapour-permeable constructions (e.g., cob, lime mortar) to balance preservation and ventilation.
Components of Compliance
- Background Ventilators: Equivalent area calculations (e.g., 8,000 mm² for habitable rooms).
- Mechanical Systems:
- Continuous Mechanical Extract Ventilation (MEV).
- Mechanical Ventilation with Heat Recovery (MVHR).
- Controls: Humidity sensors, manual overrides, and automatic boost modes.
Compliance Methods
- Performance-Based: Meet air quality targets (Appendix B of AD F).
- System-Specific: Follow prescriptive guidance for natural/mechanical systems.
- Testing: Airflow rate checks (e.g., using UKAS-calibrated equipment) and commissioning certificates (Appendix C).
Interaction with Other Regulations
- Part L (Conservation of Fuel and Power): Airtightness vs. ventilation trade-offs.
- Part J (Combustion Safety): Prevents flue gas spillage from extract fans.
- Part O (Overheating): Aligns purge ventilation requirements.
- Part B (Fire Safety): Ductwork fire resistance in compartmentalised spaces.
Practical Examples
- New Builds: MVHR systems in airtight homes (≤3 m³/(h·m²)).
- Retrofits: Adding Positive Input Ventilation (PIV) units when replacing windows.
- Commercial Kitchens: 20 l/s extract per cooking appliance (DW/172 standards).
Relevance to UK House Building & Retrofit
- Retrofit Challenges: Balancing insulation upgrades with ventilation (e.g., PAS 2035 standards).
- Energy Efficiency: MVHR systems recover 85–95% of heat from extracted air.
- Damp Prevention: Critical in retrofit projects to avoid interstitial condensation.
Additional Considerations
- CO₂ Monitoring: Mandatory in offices >125 m³ (non-domestic).
- Noise Attenuation: Required for ventilators near busy roads.
- Competent Person Schemes: Installers registered under schemes (e.g., NAPIT) can self-certify.
For further details, refer to: