What is the ventilation rate for an office?

The recommended fresh air supply rate for a general office is 10 L/s per person according to CIBSE Guide A. This equates to approximately 4-6 air changes per hour depending on occupant density.

What is the extract rate for a WC?

For a single WC or toilet, the extract rate is 15 L/s per pan (intermittent or continuous). For multiple WC areas, 6 air changes per hour (continuous) is typical. These values are from Approved Document F Volume 2 (2022).

What is the minimum ventilation rate for a classroom?

BB101 (2018) requires a minimum of 8 L/s per person for teaching spaces, with CO₂ limits of 1000 ppm time-weighted average and 1500 ppm absolute maximum during occupied hours.

Ventilation Rates by Room Type — L/s per Person & Extract Rates

Fresh Air Supply Rates (L/s per person)

Primary source: CIBSE Guide A, Table 1.5. Cross-reference with Part F Vol 2, Table 5.1 for regulatory minimums.

Space Type	L/s per person	L/s per m²	ACH (typical)	Source
Office (general)	10	1.0	4–6	CIBSE Guide A
Office (executive / meeting)	10	—	6–8	CIBSE Guide A
Classroom (primary school)	8*	—	5	BB101
Classroom (secondary school)	8*	—	5	BB101
Lecture theatre	8	—	6–8	CIBSE Guide A
Retail (general)	10	—	3–6	CIBSE Guide A
Restaurant / dining	10	—	8–12	CIBSE Guide A
Hotel bedroom	10	1.0	1–2	CIBSE Guide A
Hospital ward	10	—	6	HTM 03-01
Hospital consulting room	10	—	6	HTM 03-01
Operating theatre	—	—	15–25	HTM 03-01

* BB101 requires a minimum of 8 L/s per person for teaching spaces, but also imposes CO₂ limits of 1000 ppm time-weighted average and 1500 ppm absolute maximum during occupied hours. Always check both criteria.

Part F Vol 2 (2022) sets minimum outdoor air rates for non-domestic buildings. CIBSE Guide A gives recommended design rates, which are often higher. Always design to the more onerous requirement.

Mechanical Extract Rates

Primary source: Approved Document F Vol 2 (2022), Table 5.1a. CIBSE Guide A for supplementary values.

Space Type	Extract Rate	Basis	Source
WC / Toilet (single)	15 L/s per pan	Continuous or intermittent	Part F Vol 2
WC (multiple)	6 ACH	Continuous	Part F Vol 2
Kitchen (domestic)	30 L/s (cooker hood) / 60 L/s (range)	Intermittent	Part F Vol 1
Kitchen (commercial)	15–30 ACH	Continuous during cooking	CIBSE Guide A / DW172
Bathroom / shower	15 L/s	Intermittent	Part F Vol 2
Utility / laundry	8 L/s	Intermittent	Part F Vol 1
Car park (enclosed)	6–10 ACH	Continuous or CO-controlled	CIBSE Guide B / ADB
Plant room	5–10 ACH	Continuous when occupied	CIBSE Guide A
Server room	10–15+ ACH	Based on heat load	Design dependent
Laboratory (general)	6–15 ACH	Depends on hazard class	CIBSE Guide A
Swimming pool	4–6 ACH	Humidity control	CIBSE Guide A

Rates shown are typical design values. Specific projects may require higher rates depending on occupancy density, process loads, or contamination levels. Always verify against the relevant standard edition.

Residential Ventilation Rates (Part F Vol 1)

Approved Document F Vol 1 (2022)

Part F Vol 1 covers dwellings. Ventilation can be provided by System 1 (natural), System 2 (MEV), System 3 (dMEV), or System 4 (MVHR). Minimum whole-dwelling ventilation rates depend on number of bedrooms.

Number of bedrooms	Whole dwelling rate (L/s)	Notes
1 bedroom	13	Minimum background rate
2 bedrooms	17	—
3 bedrooms	21	—
4 bedrooms	25	—
5+ bedrooms	+4 per additional bedroom	—

Table 1.1 of Approved Document F Vol 1 (2022). Intermittent extract rates also apply to kitchens, bathrooms, and WCs.

Key Design Notes

Use L/s per person for occupancy-driven spaces such as offices, classrooms, and meeting rooms where the ventilation requirement is proportional to the number of occupants. Use air changes per hour (ACH) for extract-driven spaces like plant rooms, car parks, and WCs where air quality relates to the space volume rather than occupancy.

In most mechanical ventilation systems, supply air should be roughly equal to extract, with a slight positive or negative pressure depending on the application. Kitchens and WCs are typically negative pressure (extract-dominant) to prevent odours migrating to adjacent spaces. Clean rooms and operating theatres are positive pressure to prevent contamination ingress.

Many UK buildings use mixed-mode ventilation: natural ventilation with mechanical extract. This is common in schools (BB101 allows it) and offices. The same supply rates apply regardless of whether air is supplied mechanically or through openable windows and ventilation louvres. The question is how the air gets in, not how much.

Always cross-reference ventilation rates with Part F regulatory minimums and the relevant design guide (CIBSE Guide A, BB101, HTM 03-01). Where the design guide and regulation differ, design to the more onerous requirement.

Ventilation Rates by Room Type

Fresh Air Supply Rates (L/s per person)

Mechanical Extract Rates

Residential Ventilation Rates (Part F Vol 1)

Key Design Notes

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