Having recently signed into law new Part L Building Regulations which will require new dwellings to achieve a 40% reduction in energy consumption and a 40% reduction in related CO2 emissions from 1 July next, I can say that airtightness in buildings is an important consideration for me in meeting my objectives.

However, I feel I needto make the rather obvious, but nevertheless important, point that any measures I take to reduce energy use and CO2 emissions associated with dwellings must be based on the paramount consideration of the health, safety, comfort and well-being of the occupant.

Buildings require adequate air exchange of fresh outdoor air for indoor air to ensure that this consideration is adequately addressed, including the prevention of harmful condensation and associated mould growth and the protection of the fabric of the building. Any consideration of airtightness must be seen in this context. From an energy point of view, the more airtight the building, the less energy required to heat air introduced through lack of airtightness.

For dwellings, adequate air exchange has traditionally been provided by natural ventilation. This approach to meeting air change requirements has proven to be effective without the need for continuous operation of ventilation equipment. However, it is dependent on weather and other factors and, therefore, relatively variable.

An alternative approach is to provide continuous mechanical ventilation designed to meet minimum requirements. When properly designed and functioning correctly, this should remove most of the variability and thus improve occupant comfort. From an energy point of view, this approach involves the use of electrical energy to power the system and will increase energy use overall.

Therefore it has no attraction for me as the Minister seeking to secure energy efficiencies in buildings unless a highly efficient heat recovery system is incorporated and the building has a low air permeability. The current amendment of TGD L (Conservation of Fuel and Energy), which accompanies the new Part L Regulations, specifies a minimum efficiency for such systems. It is my intention to significantly extend this guidance in the short term by way of an early amendment of TGD F.

In summary, the issue of airtightness has to be considered in the context
of the overall design approach. There is no simple solution to this.
Mechanical ventilation with heat recovery may provide a suitable answer
in situations where there is full confidence that very low fabric permeability will be achieved and maintained through the lifetime of the building.

However, such an approach is not considered appropriate in all situations,
and provision is also made in TGD L for continuing use of natural ventilation which has the advantage that, while being more variable in practice, requires less occupant input to ensure safe and healthy operation
when compared to mechanical ventilation systems.

My new Part L Regulations have, for the first time ever, introduced a
mandatory airtightness testing requirement whereby a proportion of all
new dwellings must henceforth be tested. This is a whole new departure
in ensuring that the higher standards which I have proposed for Part L
will, in fact, be achieved.

Moreover, I have stipulated that air pressurisation test reports should be retained by the developer of the dwelling as proof of performance and that copies be included in the compulsory requirement for the provision of user information to the purchaser.

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