In his latest monthly column, retired airtight technician Trevor Clark gives us further details on building regulations:

When heating any space, there are two critical factors that help determine how efficiently it can be done.

However, the two factors also interact in a detrimental way, and this is a major cause of a ‘performance gap’.

The first factor is the ‘thermal efficiency’ of the structure, and within building regulations this is largely defined by target ‘pass’ values for key elements. These key elements are walls, floors, roofs/ceilings and windows/doors.

The ‘pass’ values are arrived at by calculating the combined individual lambda (k) values of all the section components to arrive at an overall number.

The number given in the building regulations will be the minimum required for the building.

The second factor is air leakage, which relates to unwanted air flow (draughts etc) or wanted air flow (ventilation).

Heating an insulated space may keep it warm, but if the building leaks air, then the heat (energy) will be lost and the efficiency plummets.

Too much air leakage and we lose our expensively heated air much faster than we need to, resulting in bigger heating bills and colder rooms.

The circulation of fresh air to maintain good indoor air quality is essential, so the elimination of leaks coupled with controlled ventilation is one factor in determining an associated requirement within building regulations for a certain number of air changes per hour.

Building regulations actually change more frequently than maybe thought (roughly every five years or so) and each part of the regulations may be updated at a different time.

The step-by-step approach used by the regulations currently to improve energy losses just means the buildings we are constructing will require a return visit in years to come - this will be done to improve that structure’s energy retention.