Part L of the Building Regulations (E&W) mandates that we make our buildings more airtight, then Part F insists that we ventilate them. What is this all about? Well, it’s all about control. Part L limits uncontrollable ventilation, while Part F ensures that we think about the ventilation requirements, develop a ventilation strategy, and provide ventilation in an intentional, controlled manner.
As in Approved Document L, in AD F guidance for dwellings is separate from guidance for buildings other than dwellings. Will this trend continue throughout all other future amendments? With the guidance documents becoming thicker and thicker, this would seem to me to be a sensible tactic. When designing a house, I do not need to know what would be an acceptable provision for a factory, or any other kind of building. In Scotland this is exactly what they have done. I fear this is not the intention of the ODPM.
Three types of ventilation are required. Whole building ventilation provides nominally continuous air exchange which may be reduced or ceased when the building is not occupied. It can be provided via background ventilators operating alone, or together with:
- passive stack ventilators;
- continuous mechanical extract; or
- continuous mechanical supply and extract with heat recovery.
Extract ventilation is applicable to rooms where most water vapour and/ or pollutants are released (e.g. kitchens and bathrooms). It can be provided by intermittent fans, passive stack or continuous mechanical extract with or without mechanical supply and heat recovery.
Purge ventilation is required throughout the building to aid the removal of high concentrations of pollutants and water vapour. It is commonly provided simply by opening windows and doors.
Whatever option you choose for each type of ventilation, guidance is given on the amount of ventilation you need to provide. There are additional requirements for basements and ventilation of habitable rooms through another room or conservatory.
Buildings other than dwellings
Separate guidance is given for offices, car parks and for other buildings. The ventilation provisions will not necessarily meet the cooling needs, and guidance for this is given in the new Approved Document L2a.
For all three types of building there is some common guidance (mostly in secondary referenced documents) on:
- Legionnaire’s disease.
- Recirculated air in air conditioning and mechanical ventilation.
- Access for maintenance.
Commissioning arrangements are referred directly to Approved Document L2a.
For the purpose of Part F, rooms containing printers and photocopiers, office sanitary accommodation and washrooms, and specialist buildings or spaces (e.g. commercial kitchens and sports centres) are also classed as offices.
The Approved Document describes four ways of complying with the regulations:
Provide ventilation which meets the stated airflow rates. This approach is similar to that for dwellings where the three types of ventilation – whole building, extract and purge – need specific provisions. Guidance is given on the required ventilation rates.
- Provide natural ventilation to achieve the stated rates.
- Follow the recommendations of CIBSE Application Manual AM13:2000 and CIBSE Guides A and B2.
- Use other ventilation systems and submit proof that they can meet the moisture and air quality criteria set out in Appendix A to AD F.
The requirements will be satisfied if the mean calculated predicted pollutant levels do not exceed the levels stated. Alternatively buildings can be naturally ventilated by providing openings no smaller than 1/20th of the floor area, of which at least 25% should be on each of two opposite walls. This area of opening can be halved if the ventilation is supplemented by a mechanical system capable of at least 3 air changes per hour. Basement car parks must have mechanical systems capable of 6 air changes per hour. Additional provisions are necessary where cars queue inside the building.
Other types of building
The requirements will be satisfied by following specific secondary design guidance documents. There are 46 references to secondary documents covering 29 types of buildings. For common spaces where large numbers of people are expected to gather, e.g. shopping malls and foyers, natural ventilation with a minimum total opening of 1/50th of the floor area or mechanical ventilation to give 1 L/s per m2 of floor area must be provided.
Section 3 of AD F deals with work on existing buildings. The actual work to the building must comply with the new Part F, whilst the remainder of the building should not be made less satisfactory than before the work was carried out.
Replacement windows have to comply with Parts L and N and should not have a worse level of compliance under Parts B, F and J than the windows they replace.
Specific provisions are given for the addition to an existing building of:
- A habitable room.
- A wet room.
- A conservatory with a floor area
- exceeding 30 m2.
The trend for recently published Approved Documents is to rely heavily on secondary documents. The new AD F follows this trend and refers to 14 British Standards and 34 other documents. Although this keeps the thickness of the Approved Documents down, it does mean that in order to ensure compliance with all the Building Regulations, you need to have to hand a veritable library of references, so don’t forget to keep up your subscription to The Construction Information Service.