Put simply, ventilation is the removal of ‘stale’ air from inside a building and its replacement with ‘fresh’ air from outside. Adequate ventilation is essential in your home to maintain a healthy environment but also to prevent the build-up of excess levels of humidity and to provide air for fuel-burning appliances. A good ventilation system will help remove cooking smells, allergens and other irritants, such as tobacco smoke, and make your home a considerably more pleasant, healthy and comfortable place to live.

Buildings are ventilated through a combination of air infiltration and purpose-provided ventilation. Infiltration is the uncontrollable air exchange between inside and outside a building through a range of air leakage paths in the building structure i.e. drafts. Purpose-provided ventilation is the controllable air exchange by means of a range of natural and/or mechanical devices in windows and electric extract fans.

The current aim of the Building Regulations is to minimise uncontrollable infiltration ventilation in favour of controllable ventilation in order to help improve energy efficiency.

The different types of ventilation required in the home are currently dealt with by three parts of the Building Regulations: Part F deals with ventilation to the living space, Part C ventilating the structure and Part J the provision of air for fuel-burning appliances, including fires and stoves.

The new Part F (ventilation) document is more performance based and gives guidance on how required measures can be achieved, giving an overview of a number of ventilation solutions.

• The changes in Part L (energy efficiency) require buildings to be better sealed and more airtight, so the new Part F provisions are designed to ventilate buildings having air permeability down to 3 m3/h/m2 at 50 Pa.
• Guidance has been given for the ventilation of basements in houses.
• More guidance has been given for domestic mechanical and natural ventilation systems.
• Requirement F2, regarding ventilating the structure, has been moved to Part C.
• Appendixes give guidance on passive stack ventilation system design and installation, good practice on the installation of fans in dwellings and on minimising ingress of external pollutants into buildings in urban areas.

The changes to the Building Regulations tie Parts L and F closer together. This is because ventilation is rapidly becoming the greatest source of heat loss in new dwellings as the standard of insulation continues to improve. The revised Part L places a great emphasis on making buildings as airtight as possible and, from April, air pressure leakage testing will become a mandatory requirement for all constructions, including dwellings, to measure air permeability and show any unacceptable leakage. This in turn places a greater importance on controlled, purpose provided ventilation as opposed to infiltration.

Pressure testing will cost around £4-500 per property, but can potentially be avoided for self-builders if it can be demonstrated that, during that 12-month period, a dwelling of the same type constructed by the same builder has been pressure tested and achieved the required design air permeability, or more likely, by using a value of 15m3/(h.m2) when calculating the Dwelling Carbon Emissions Rate.

The effect of using this worst-case value would then have to be compensated for by improving standards of energy efficiency elsewhere in the dwelling. Options for compensating include improving the elemental U-values in floors, walls, roof and windows, a better boiler SEDBUK rating or the inclusion of renewables such as solar panels, a heat pump and photovoltaic ventilation, either through natural means (such as opening windows to each room) or where there are no windows, a mechanical fan.

You might also wish to provide extraction above the kitchen hob. This can be incorporated into a whole-house system but it is generally considered best to keep this separate due to the high levels of grease and moisture produced in kitchens. Kitchen extractors can be ducted to the outside, or can filter out cooking smells and return the cleaned air back into the kitchen.

When considering ventilation it is important to remember that the roof structure and any voids beneath suspended floors and ceilings need to be ventilated under Part C of the Building Regs and under Part J ventilation is required for fires and stoves.