Part F provides guidance on natural and mechanical ventilation. For natural ventilation, it requires a means of "rapid ventilation" using opening windows, and background ventilation by trickle vents or airbricks. For the mechanical ventilation of non-domestic buildings, it insists on a minimum of 8 l/s a person of fresh air.
And this is where Part L comes in. Under proposals to increase the airtightness of buildings, the amount of trickle ventilation will also have to rise to ensure sufficient background ventilation and control condensation problems. And as air-conditioned commercial buildings become more airtight, the fresh air requirements are also likely to increase. As a DETR spokesperson explains: "The airtightness measures in Part L will need to be finalised before we can consider ventilation."
When the DETR does get round to reviewing Part F, another area that it must consider is passive stack ventilation in kitchens, utility rooms and bathrooms.
Passive stack ventilation is based on warm air rising through a duct. The ventilator will control excess water vapour produced by cooking, but this is only relevant in winter when condensation is a problem. However, the vents will continue to suck out warm air even when a room does not need ventilating, which can lead to energy being wasted.
In summer, the system does the exact opposite of what it is supposed to do. If it is cooler inside than out, a passive stack ventilator will supply air to the room from outside. So if you burn the toast on a summer morning, the system won't extract the smell.
Still in the kitchen, there is another problem with the extract ventilation rates. Although they will control condensation, they are not enough to enable a cooker extract hood to work properly – watch out for this when specifying an extract rate for a hood. And for kitchens with a solid fuel appliance, Part F forbids mechanical extract because it could suck flue gases into the kitchen – a problem often overlooked in the design of "rustic" kitchens.
But this is all for the future, and with the revisions to Part L not expected until summer, it may be worth investing in a new toaster.
Part F: VentilationPart F covers ventilation and includes measures to stop condensation in roofs. A review is being considered once the new Part L comes into force. The Approved Document:
- Recommends ventilation rates for rooms with openable windows, including the size of the opening needed for background ventilation
- Recommends extract rates for rooms with mechanical extract
- Recommends ventilation rates for general, communal and specialist areas in non-domestic buildings, including guidance on fresh air rates
- Provides guidance on the design of mechanical ventilation and air-conditioning plant, including access for maintenance
- Offers guidance on the ventilation of roofs.
Brian Mark is a partner in environmental consultant Fulcrum Consulting.