Air vs energy

Part F of the Building Regulations requires "adequate means of ventilation for people in the building". More succinctly, it's about fresh air. Part L is all about "conservation of fuel and power", or saving energy (and cutting carbon dioxide emissions). One way to do this is to stop heat, and therefore air, from leaking out of a building. So Part F and Part L could be in potential conflict. New editions of Approved Documents F and L are currently in the ODPM pipeline, so how are Mr Prescott's team attempting to avoid conflicting requirements?

Performance not prescription

The new editions of Parts F and L both follow the current trend towards performance-based regulations. In other words, they tell us what to achieve, but not necessarily how to achieve it. In Part F we are told what level of ventilation should be sufficient, but how we deliver that level of ventilation is up to the designer. The revised Part F is now expected to give three options for providing "adequate means of ventilation" in both dwellings and other buildings.

At home …

In homes the first option is to extract air from kitchens, toilets, bathrooms and utility rooms (any room that produces water vapour or odours), and then ensure adequate air supply to the whole building, and purge ventilation for each habitable room. The second option is to follow the system guidance in the Approved Document. The third option will be anything else the building inspector agrees will meet the performance requirement.

The first option involves following the requirements in two short tables and then ensuring adequate purging capacity. The second option covers specified types of ventilation system: background ventilators with intermittent extract; passive stack; continuous mechanical extract and continuous mechanical supply; and extract with heat recovery. It is not at all clear why heat recovery is required, rather than being optional. It has advantages over simple supply and extract systems, although they ventilate effectively without heat recovery at a lower initial cost. Part F seems to be straying into Part L territory here.

The Approved Document is likely to give a number of worked examples to show how the specified systems might be configured, which will both assist their use and gives flexibility to designers. The third option provides flexibility to deal with unusual situations but is unlikely to be used routinely.

… and at work

The guidance for "buildings other than dwellings" covers offices, car parks and other building types. There are three options for office ventilation. The first is very similar to option one for homes: extract, provide adequate whole building ventilation and purge capacity, as set out in tables in the Approved Document. The second option refers the designer to existing guidance in CIBSE Guide A, Environmental Design, and CIBSE Applications Manual 10 on Natural Ventilation, which has just been fully updated in anticipation of the revised regulations.

Otherwise, the designer may follow the guidance given in CIBSE Applications Manual 13 on Mixed Mode Ventilation, and in CIBSE Guide B2 on Ventilation. Guide B2 also underpins the approach to other building types with an extensive table summarising the appropriate design guidance documents. In addition to the CIBSE guide there is reference to Health Technical Notes, DfES Building Bulletins, Prison and Court Service guidance and the Welfare of Farm Animals Regulations. For non-domestic buildings the performance approach and the need to demonstrate that a design solution delivers the required result is very much the flavour of the revised Approved Document.

Saving energy - cutting carbon

Whereas Part F is the "Tunes" of Building Regulation - helping us breathe more easily - Part L is all about cutting carbon dioxide emissions. It is likely that the revised requirement in Part L will explicitly link energy saving (conservation of fuel and power in regulation speak) with cutting emissions. The Approved Documents - all 4 of them: L1 dwellings and L2 other buildings, 1A and 2A for new and 1B and 2B for refurbishment - will then give guidance on ways of meeting the performance requirement.

A key requirement in the new Part L relates to airtightness testing. It remains to be seen what exactly these will be. A leaking building leaks heat. The more it leaks, the higher the cost in pounds sterling and kilograms carbon dioxide. (And in hot weather, which we expect to see and feel more and more in the future, leaky buildings may get warmer more quickly.)

Testing, testing

Mandatory pressure testing would address this. Everyone knows what to do: if they don't they'll be found out and have to put it right. And airtightness is a good proxy for overall build quality. Mandatory testing was introduced in Sweden many years ago. The industry there has now learned to build tight, and mandatory testing has been dropped. The same could be done here. It would cause some initial upheaval, as everyone adapts. But good contractors will soon realise the benefits of getting it right first time, and the market will do the rest. The alternative is random or discretionary testing, which has not worked over the last three years.

Another key interface between Parts L and F is commissioning. Once systems are in buildings, they need to be set up to work. CIBSE is keen to see requirements for commissioning to be carried out and to be checked - again, what is the problem of telling everyone what is required and expecting them to do it? Systems that are not commissioned properly will not work properly. They will inevitably cost more, possibly a lot more, to run. They are unlikely to ventilate effectively or be energy efficient. Failure to commission isn't just a short cut on Part L - it jeopardises ventilation effectiveness and increases running costs .

Finally, there will be a link between Part F and Part L on energy consumption. Part L is moving to a whole building energy calculation. Energy efficient ventilation systems will be a plus, and those that ventilate and recover heat, or use solar gain to warm the supply air, will reduce overall energy consumption. In dwellings this could be a major advantage, offering reduced running costs for the life of the system.

So the new F and L offer opportunities for joined-up thinking from designers, as well as some interesting challenges.