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With the introduction of new guidelines on comfort and air quality in schools, the editor of Modern Building Services, Karen Fletcher dives into the detail.

The document BB101 Guidelines on ventilation, thermal comfort and indoor air quality in schools was updated in August 2018, and it sets some tough targets for building services. 

The document addresses three key services-related areas in school buildings: ventilation; thermal comfort; and indoor air quality (IAQ) – and introduces higher standards for all of them.

With the August 2018 update, which replaces BB101 2016, government has now aligned BB101 with the latest health and safety standards, and also aims to improve thermal comfort and IAQ with a  view to creating ‘healthier outcomes for students’.

The document sets out standards for all spaces within a school

Karen Fletcher Karen Fletcher Editor of Modern Building Systems

A tougher approach

Designers, contractors and installers will see that BB101 has toughened its approach to several areas.

There are more stringent air quality targets; tougher rules on summertime overheating; and a strong focus on avoidance of draughts. The elements of IAQ, thermal comfort and energy efficiency must be carefully balanced under the new rules.

The government’s approach sets the bar high for performance of ventilation systems. Classroom guidelines include maximum CO2 limits which cannot be breached for 20 consecutive minutes.

BB101 2018 also introduces hybrid ventilation systems along with the traditional natural and mechanical ventilation approaches – which gives designers another option to consider. 

The document sets out standards for all spaces including halls, classrooms and specialist practical areas such as science labs and design and technology spaces. It sets maximum levels of carbon dioxide in teaching spaces and minimum ventilation rates in practical spaces and specialist accommodation, for example for pupils with special needs.

What are the requirements?

Required CO2 levels depend on the type of ventilation system being applied:

* Natural ventilation – average CO2 level must be less than 1500ppm (or 5l/s per person)

* Hybrid/mixed mode/mechanical ventilation – average CO2 must less than 1000ppm (8 l/s)

Indoor air quality is of course on the political agenda at the moment, particularly in cities such as London, where pollution levels are rising steadily. BB101 brings requirements for IAQ in line with the World Health Organisation (WHO) performance levels.

And it also has an eye to reducing pollutant ingress into school buildings, including guidance on how to meet maximum exposure level for pollutants and ways to reduce the level of outdoor pollutants such as NOx and traffic particulates.

This includes the location of air intakes and exhausts, the management of openable windows, and filtration of supply air.

Coping with heat

With more heatwaves like those experienced in Summer 2018 expected in the UK, it’s no surprise that overheating is also in the sights of BB101.

An important point to note here is that full occupancy is now to be assumed throughout the holiday period. And the rules state that there should be no more than 40 hours between 1st May to 30th September when the temperature is 1oC above the allowable maximum.

BB101 has detailed calculation methods for thermal comfort. Adaptive thermal comfort calculations have been introduced to prevent summertime overheating based on the latest research on how people adapt to higher temperatures.

These calculations use variable maximum indoor temperatures that depend on the outside temperature. This helps to avoid the unnecessary use of air conditioning by using passive measures such as night cooling and thermal mass to cool spaces in summertime.

Holistic and multi-disciplinary approach

One interesting aspect of BB101 is that it acknowledges that sometimes building design can become very focused on a single outcome, such as reducing energy use in a building. This can, for example, result in the use of natural ventilation strategies which then cause problems with overheating and poor IAQ.

With this in mind, the document states: ‘A holistic, multi-disciplinary approach prevents unintended consequences of design driven by a low energy or other overarching design drivers.”

The document is keen to ensure that designers put building users and the people responsible for operating the school, first. It states: ‘As well as the environmental design factors, the building occupants and facilities management team should be considered.

For example:

  • The facilities management team need to understand the building environmental systems and controls

  • The staff need to understand the basic building operation and occupant controls

  • The designers need to understand the occupants’ needs and their behaviour in use of the space’

Final thoughts

While this refers to schools, it applies equally to offices, hospitals, leisure centres and every other building that’s used by people.  In many ways, what BB101 describes is an example of how all buildings and building services should be designed: with occupants the focal point of the whole exercise.

BB101 Guidelines on ventilation, thermal comfort and indoor air quality in schools  can be downloaded free here:

Karen Fletcher is editor of Modern Building Services