BB101 school ventilation: what it requires and what to do when a classroom fails it

BB101 (Building Bulletin 101) is the Department for Education’s guidance on ventilation, thermal comfort and indoor air quality in schools, and its main test for a classroom is CO2: a daily average below 1,000 ppm with mechanical ventilation, or below 1,500 ppm with natural ventilation, measured while the room is occupied. Rossair surveys classrooms against BB101, finds where ventilation and temperature fall short, and carries out the mechanical, hybrid or controls work to put it right, planned around term dates.

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What we deliver

Ventilation surveys and fixes for school buildings

A BB101 survey compares what a room does in use with what the guidance asks for. BB101 itself recommends monitoring typical north, south, east and west facing classrooms and other key spaces, and recording temperature and CO2 through the building controls. We do the same: log CO2 and temperature in representative rooms, check the vents, openable windows, fans, air handling units and controls that feed them, and report room by room. The cause is often simpler than the school expects: a control set point, a failed damper, a blocked vent or a unit that was never serviced. Where a room cannot meet the target with the equipment it has, we cost the mechanical or hybrid option.

CO2 and temperature logging in representative classrooms through the heating season and into summer
Check of vents, openable windows, fans, air handling units and their controls
Findings against the BB101 CO2 and overheating criteria, room by room
Low-cost fixes first: control settings, repairs, cleaning and servicing
Mechanical, hybrid or heat recovery ventilation retrofits where natural ventilation cannot meet the target
Commissioning, BMS monitoring and handover records, so the result can be shown to be holding

Commercial plant room with pressure vessels, water treatment and ductwork

BB101 in detail

What BB101 requires, and the guidance around it

Figures come from the 2018 edition of BB101, which GOV.UK still lists as current, and from DfE’s February 2026 guidance on ventilation and CO2 monitors. Recheck GOV.UK before you rely on any figure for a contract or a bid.

CO2 targets in teaching rooms

With mechanical ventilation, or a hybrid system running in mechanical mode, the daily average CO2 should be below 1,000 ppm while the room is occupied, and should not exceed 1,500 ppm for more than 20 consecutive minutes a day. With natural ventilation, or hybrid in natural mode, the limits are 1,500 ppm daily average and 2,000 ppm for no more than 20 consecutive minutes. Both apply at or below the design occupancy and are measured at seated head height. BB101 says these standards must be followed for a building to comply with it.

Ventilation rates

BB101 notes that in a typical classroom of 30 pupils and two staff, about 8 to 9 litres per second of outdoor air per person holds CO2 near 1,000 ppm, and 5 litres per second per person holds it near 1,500 ppm, in steady state. For science laboratories and preparation rooms over 70 m² the minimum exhaust rate is 4 l/s per m² of floor area, with a way to boost to at least 5 l/s per m². Art rooms and workshops need 2.5 l/s per m².

Science, D&T and food rooms

CO2 is allowed to rise higher during practical work, but gas-fired equipment has its own limits. Where a room has only Type A gas appliances such as Bunsen burners, BB101 sets a warning level of 2,800 ppm and an automatic gas shut-off at 5,000 ppm, taken from IGEM/UP/11. It also says openable windows alone are not an adequate way to control CO2 in these spaces. Fume cupboards sit inside the same ventilation design.

Fume cupboard testing

Classroom temperatures in winter

BB101 recommends a normal maintained operative temperature of 20°C in teaching spaces during the heating season (1 October to 30 April), with a maximum of 25°C at full occupancy. Special schools and resourced provision for pupils with complex needs are set at 23°C, and circulation spaces, toilets and sports halls at 17°C. These are design values, measured at seated head height in the centre of the room, not legal limits.

Summer overheating

BB101 assesses overheating with the adaptive method in CIBSE TM52. The minimum requirement is that a room is 1°C or more above its adaptive threshold for no more than 40 hours between 1 May and 30 September, counting 9am to 4pm on weekdays. As an upper limit, no room should be more than 4°C above the threshold. BB101 says mechanical cooling should not normally be needed in general teaching spaces with ICT heat gains below 15 W/m², so shading, ventilation and night cooling come first.

Air conditioning for schools

CO2 monitors in daily use

DfE’s guidance reads a monitor in three bands: under 800 ppm is good, 800 to 1,500 ppm is adequate and worth opening windows or doors for, and over 1,500 ppm is poor, so increase ventilation where you can. In cold weather it suggests partly opening windows and doors, opening higher windows to cut draughts, and airing rooms between uses, for example 10 minutes an hour. These bands manage a room day to day. They are a different test from the BB101 daily-average targets.

The law behind it

The Workplace (Health, Safety and Welfare) Regulations 1992 apply to schools. Regulation 6 requires every enclosed workplace to be ventilated by a sufficient quantity of fresh or purified air. Regulation 7 requires a reasonable temperature and says excessive effects of sunlight must be avoided. The School Premises (England) Regulations 2012 set no classroom temperature; they require premises to be maintained so that pupils’ health, safety and welfare are ensured so far as reasonably practicable.

Existing buildings

BB101 is written for new schools and refurbishments, and Approved Document F refers schools to it. For a building already in use, the legal duty comes from the Workplace Regulations. DfE states that its BB101 CO2 standards ensure compliance with regulation 6, which makes them the practical benchmark for an existing classroom.

When a mechanical or hybrid retrofit is worth it

Fix the cheap causes first: controls, repairs, cleaning, servicing. A retrofit is worth costing when rooms still exceed the target with everything working, when windows stay shut in winter because of draughts, noise or outdoor air quality, or when an over-glazed or ICT-heavy room overheats. Heat recovery limits the heating penalty; BB101 asks for room-based heat recovery units to reach a heat recovery efficiency factor of at least 75%. BB101 also says mechanical ventilation should not be the only summertime ventilation in occupied rooms.

Building management systems

Funding ventilation work

Ventilation that addresses a genuine building condition need can form part of a Condition Improvement Fund bid. We support CIF bids for heating, ventilation, water and electrical projects with a costed options appraisal and a fixed-price quote, then deliver the funded works.

Condition Improvement Fund bids

School and college ventilation we have designed and maintained

20+

Years at Chichester College Group

Campuses under one PPM contract

Science labs at Sacred Heart High School

£820k

Mechanical and BMS, Sacred Heart

We have maintained the Chichester College Group estate for over 20 years, across 11 campuses including Chichester College, Brinsbury, Haywards Heath, Worthing and Met College Brighton, under one PPM contract. At Sacred Heart High School in Hammersmith we designed and installed the mechanical services and BMS for a science block with 10 laboratories and a four-court sports hall, including supply and extract ventilation and heat recovery, and we commissioned the sports hall natural ventilation.

Compliance

Standards and guidance a school ventilation survey is judged against

BB101DfE’s 2018 guidelines on ventilation, thermal comfort and indoor air quality in schools: CO2 targets, ventilation rates, temperatures and overheating criteria.
Workplace RegsWorkplace (Health, Safety and Welfare) Regulations 1992: regulation 6 on ventilation and regulation 7 on a reasonable temperature and sunlight.
Approved Doc FThe Building Regulations ventilation document, which refers schools to BB101.
CIBSE TM52The adaptive thermal comfort method BB101 uses to assess summertime overheating in free-running rooms.
DfE CO2 guidanceVentilation and air quality in education and childcare settings (February 2026): how to read a CO2 monitor and what to do at each band.
School PremisesSchool Premises (England) Regulations 2012: premises maintained so pupils’ health, safety and welfare are ensured so far as reasonably practicable.

Related education pages

More for school and college estates

Education estates hubHVAC maintenance, PPM and MEP work for schools, academies, colleges and universities.Compliance for schoolsOne building services checklist mapped to DfE’s estate management guidance.Air conditioning for schoolsCooling for classrooms, server rooms and halls, with TM44 and F-Gas covered.Building management systemsControls and monitoring that log temperature and CO2 and keep set points right.Fume cupboard testingScience lab fume cupboards examined and tested at least every 14 months.Condition Improvement FundCIF bid support and delivery for heating, ventilation and electrical projects.

Frequently asked

Questions about BB101 and school ventilation

What is BB101?

BB101 is Building Bulletin 101, the Department for Education’s guidance on ventilation, thermal comfort and indoor air quality in school buildings. The current edition was published on GOV.UK in 2018. It sets CO2 targets for teaching rooms, minimum ventilation rates for practical spaces, recommended winter temperatures and a method for assessing summer overheating. It is written for new schools and refurbishments, and Approved Document F refers schools to it.

What CO2 level does BB101 allow in a classroom?

With mechanical ventilation the daily average while the room is occupied should be below 1,000 ppm, and CO2 should not exceed 1,500 ppm for more than 20 consecutive minutes a day. With natural ventilation the figures are 1,500 ppm and 2,000 ppm. CO2 is measured at seated head height. For day-to-day monitoring, DfE’s separate guidance calls readings under 800 ppm good, 800 to 1,500 ppm adequate and over 1,500 ppm poor.

What is the minimum temperature in a school classroom?

There is no statutory minimum classroom temperature in England: the School Premises (England) Regulations 2012 set none. The Workplace Regulations 1992 require a reasonable temperature, and HSE says that is usually at least 16°C, or 13°C for strenuous work. BB101 recommends a design temperature of 20°C in teaching spaces during the heating season, with 23°C for pupils with complex needs. Wales has its own regulations.

What is the maximum temperature in a school classroom?

There is no legal maximum. The Workplace Regulations require that excessive effects of sunlight on temperature are avoided, and HSE sets no upper limit for workrooms. BB101 deals with heat through its overheating assessment, which limits the hours a room can run above its adaptive comfort threshold between May and September. DfE’s June 2026 hot weather advice for schools says fans can be used to increase air movement when temperatures are below 35°C.

Does BB101 apply to existing schools?

BB101 is design guidance for new buildings and refurbishments, so the Building Regulations do not require an existing classroom to be retrofitted to it. An existing school still has a duty under the Workplace Regulations to ventilate its rooms with sufficient fresh air and keep temperatures reasonable. DfE says its BB101 CO2 standards ensure compliance with the ventilation regulation, which is why most schools use them as the benchmark.

How does a BB101 ventilation survey work?

We log CO2 and temperature in representative classrooms and other key spaces, check the vents, windows, fans, air handling units and controls that serve them, and compare the results with the BB101 CO2 and overheating criteria. The report goes room by room and separates quick fixes, such as control changes, repairs and servicing, from rooms that need new ventilation equipment. Where equipment is needed, we cost mechanical and hybrid options.

When is mechanical or hybrid ventilation worth fitting to a school?

When monitoring shows a room still misses the CO2 target with its existing vents and controls working, when windows stay closed in winter because of cold draughts, noise or poor outdoor air, or when a heavily glazed or ICT-heavy room overheats. Heat recovery reduces the extra heating load. Mechanical ventilation should not be the only summer ventilation in an occupied room, so BB101 still expects openable windows or vents alongside it.

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