Step-by-Step Guide to Meeting UK Purge Ventilation Requirements (Part F)
Understanding When and How to Provide Adequate Ventilation in Dwellings
1. Start With the Basics: Is Purge Ventilation Required?
All habitable rooms (living rooms, bedrooms, dining rooms, etc.) in UK dwellings must comply with Part F ventilation requirements. Begin by asking:
Q: Is the space a habitable room?
- Yes: Proceed to ventilation checks.
- No (e.g., bathroom, kitchen, utility room): Focus on extract ventilation instead (see Part F Section 1 for wet room requirements).
2. Natural Ventilation First: Window Requirements
A. Check for Openable Windows
All habitable rooms must have openable windows or another purge ventilation system. Ask:
Q: Does the room have openable windows?
- Yes: Evaluate window type/size.
- No: Mechanical purge ventilation is required (e.g., extract fan with ≥4 air changes/hour).
B. Window Type Dictates Minimum Opening Area
The required open area depends on window style:
| Window Type | Minimum Open Area | Example (10m² Room) |
|---|---|---|
| Hinged/pivot (opens ≥30°) | 1/20 of floor area | 0.5m² opening (e.g., 71cm x 71cm) |
| Hinged/pivot (opens 15-30°) | 1/10 of floor area | 1.0m² opening (e.g., 100cm x 100cm) |
| Sash windows | Must open fully to 1/10 floor area | 1.0m² opening |
| Other (e.g., tilt-and-turn) | Total open area ≥ 1/20 floor area | 0.5m² opening |
Example Calculation:
A 15m² living room with hinged windows (opens 35°) needs:
15m² × 1/20 = 0.75m² of open window area.
3. When Natural Ventilation Isn’t Enough
A. Upgrade or Install Mechanical Systems
If existing windows can’t meet the minimum open area, you must:
- Enlarge the window opening, or
- Install mechanical purge ventilation (e.g., continuous extract fan rated for ≥4 air changes/hour).
B. Overheating Risks (Part O Compliance)
South-facing rooms or spaces with large glazing often require enhanced purge ventilation to prevent overheating. Ask:
Q: Is the room at risk of overheating?
- Yes: Follow Part O regulations (typically requires larger openings or night-time ventilation).
- No: Proceed with Part F requirements only.
4. Special Cases: High-Pollutant Activities
Rooms used for activities like painting, woodworking, or frequent cooking may need additional ventilation:
- Temporary boost mode: Use mechanical systems with ≥30 l/s extract rates.
- Larger openings: Increase purge ventilation capacity by 20-50% above minimum requirements.
5. Final Compliance Checklist
- ✅ All habitable rooms have purge ventilation (natural or mechanical).
- ✅ Window openings meet size/type requirements (see table above).
- ✅ Mechanical systems (if used) are commissioned and tested (refer to Part F Appendix C).
- ✅ Overheating risks addressed via Part O where applicable.
Need Help?
Consult a competent ventilation specialist if:
- The room has no external walls.
- You’re unsure about airflow calculations.
- Retrofitting ventilation in listed/traditional buildings.
By following this guide, you’ll ensure compliance with Part F while maintaining healthy indoor air quality. Always cross-check with the full Approved Document F for edge cases or complex projects.