School ventilation and cooling: what BB101 requires

What is BB101 and who has to meet it?

BB101 is the Department for Education's guidance on ventilation, thermal comfort and indoor air quality in school buildings. GOV.UK describes it as guidance "to support the design and performance standards" for those three things, "used to satisfy Section 1: Ventilation for schools in Approved Document F". DfE's estate guidance says it "sets out the standards for air quality in new and refurbished school buildings". The BB101 page was last updated on 23 August 2018. DfE's newer operating guidance, published on 24 February 2026, applies to England (DfE). Approved Document F is the building regulation for ventilation in England; its Volume 2 applies to buildings other than dwellings, and the 2022 edition came into force on 15 June 2022.

This page does not restate BB101's numerical limits. GOV.UK publishes the document as a Word file rather than web text, so take limits from the current document, or ask the designer to cite the clause. What the web guidance does give is how to read a classroom in use.

What do classroom CO2 readings mean?

DfE's operating guidance reads CO2 against two thresholds. These are monitoring bands for a building in use, not BB101's design limits.

Reading	DfE's description	Suggested response
Under 800 ppm	Ventilation is good	In winter, consider partly or fully closing windows
800 to 1,500 ppm	Ventilation is adequate	Consider opening windows or doors
Over 1,500 ppm	Ventilation is poor	Increase ventilation where you can

One sensor is enough for a typical classroom, placed away from doors, windows and ventilation outlets, at table or head height and at least 0.5 m from occupants. HSE agrees that levels "consistently higher than 1500ppm in an occupied room indicate poor ventilation", but reminds readers that CO2 is "only a broad guide" and does not demonstrate "safe levels".

How do natural, hybrid and mechanical ventilation compare?

DfE says ventilation can be natural (open windows, doors or vents), mechanical (fans or ducts bringing in outdoor air) or a combination. Its estates guidance says to "plan for mechanical or hybrid (a combination of natural and mechanical) systems where natural ventilation is not sufficient" (Improve and renew).

• Natural ventilation depends on windows that open, the weather and the people using them. DfE lists "windows are not painted shut and are safe to open" and filters being "checked, cleaned and replaced" as basic maintenance.
• Hybrid adds fans or controls to windows and vents for the days natural ventilation falls short.
• Mechanical supplies a set airflow. A unit in each room is the idea behind decentralised MVHR, and demand-controlled ventilation varies airflow with CO2.

Air cleaning units are not an alternative: DfE says "they are not a substitute for ventilation". The commercial ventilation cost page explains what drives a mechanical system's price.

When do ventilation upgrades come before cooling?

1. Measure. Log CO2 and temperature in the rooms of concern across a term.
2. Fix the basics. Windows, vents, filters and controls come first.
3. Cut summer heat at source. DfE advises "external shading, tree planting and glazing upgrades to limit overheating and improve user comfort".
4. Add mechanical or hybrid ventilation where natural cannot deliver the airflow.
5. Cool only what is left. Add cooling for rooms whose heat load ventilation and shading cannot meet.

DfE says "a strategic approach to ventilation and shading can limit reliance on mechanical cooling". Its Met Office and UCL modelling gives the stakes: "when indoor temperatures reach 35°C, learning could become very difficult", and "some schools may already experience one or two days a year like this" (DfE). Where cooling is added to a ventilation unit, see MVHR with cooling.

Which school rooms genuinely need cooling?

DfE's energy guidance says air conditioning is "typically used in server rooms, reprographic rooms and ICT classrooms" and should run "no cooler than necessary", adding that "most server rooms need not run any lower than 21°C". The BB101 calculation tools include an ICT equipment heat gains calculator for classrooms and a CO2 concentration build-up calculator, both "for use at the early stages of design". Server rooms have their own guide: server room cooling requirements.

What duties come with air conditioning and extract in a school?

DfE's guidance sets out three:

• air conditioning "must be inspected by an energy assessor regularly, at least every 5 years", as the TM44 guide explains;
• F-gas leak checks, where the frequency "will vary between 3 and 12 months, depending on the amount of F gas in the equipment";
• local exhaust ventilation in workshops, which "should be examined and tested at least every 14 months".

What should a bursar or trust estates team ask a ventilation contractor?

• Which BB101 clause or performance criterion does the design meet, and how will it be shown at handover?
• What CO2 and temperature data from the existing rooms informed the design?
• Who cleans and replaces filters, how often, and is access safe without closing the room?
• How do controls respond to CO2 and to summer heat, and who can change the settings?
• What is the commissioning record for each room, as in the handover guide?
• Which works fit school holidays, and what stays running in term time?

The background duties are in commercial ventilation requirements and the system families on the ventilation and MVHR page. Costs depend on airflow, unit type, ductwork and controls, as the cost page sets out.

How is an occupied school refurbished?

DfE says to group interventions, with coordination covering "contractor access, programme length and opportunities to align works with planned maintenance or holiday periods". Two cautions apply to ventilation work. Window replacement "must be supported with calculations carried out by a suitably qualified professional to ensure the required ventilation rates are achieved", and tightening a building without adding ventilation "can increase the risk of condensation and poor air quality". You can send an enquiry through the form to ask for quotes against your own room list.

Sources

• Ventilation, thermal comfort and indoor air quality: BB 101, Department for Education, GOV.UK, updated 23 August 2018, checked 22 October 2026
• Calculation tools: BB 101, Department for Education, GOV.UK, updated 23 August 2018, checked 22 October 2026
• Ventilation and air quality in education and childcare settings, Department for Education, GOV.UK, updated 24 February 2026, checked 22 October 2026
• Good estate management for schools: health and safety, Department for Education, GOV.UK, updated 20 July 2026, checked 22 October 2026
• Improve and renew your long-term estates plan, Department for Education, GOV.UK, updated 25 February 2026, checked 22 October 2026
• Energy efficiency: guidance for the school and further education college estate, Department for Education, GOV.UK, updated 6 December 2022, checked 22 October 2026
• Impact of UK climate change risk on the delivery of education: overheating, flooding and water scarcity, Department for Education, GOV.UK, updated 19 June 2025, checked 22 October 2026
• Ventilation in the workplace: using CO2 monitors, HSE, checked 22 October 2026
• Ventilation: Approved Document F, MHCLG, GOV.UK, updated 15 June 2022, checked 22 October 2026

Frequently asked questions

Can an air cleaning unit replace ventilation in a classroom?

No. DfE says air cleaning units are not a substitute for ventilation and should not be a reason to stop opening windows or using mechanical ventilation. They can be a stopgap where fresh air cannot be maintained until remedial works are done.

Does a school have to monitor CO2?

DfE says schools should regularly monitor ventilation and air quality across their buildings, and that CO2 monitoring helps identify poorly ventilated spaces. DfE will not replace faulty devices it supplied or pay for replacement filters, so those costs fall to the school.

How hot is too hot for a classroom?

DfE says learning could become very difficult when indoor temperatures reach 35°C. BB101 covers thermal comfort in its design and performance standards, which this page does not restate. HSE separately says there is no law for a maximum working temperature, so the school's own risk assessment and BB101 guide the response.