Principles of air tigtness for new house extensions
Airtightness is all about avoiding gaps – gaps in contractual arrangements and the design
process as well as those between components and those left during installation. They are usually caused either by a
lack of awareness of the importance of airtightness or by a lack of contractual responsibility for ensuring
Airtightness needs to be a priority throughout the construction process – before, during and after.
The adoption of an ‘airtightness strategy’ should be seriously considered (see Box 1).
Airtightness should be considered at every stage of the design process. The line of the airtightness barrier
should be established very early on. One way of doing this is to mark a set of drawings with a red line. This
should be a continuous line around the building, passing through all elements in the building that separate heated
and unheated spaces (see Figure 16).
Identify areas where additional detailing will be required and apportion responsibility for design and
construction of the air barrier. Provided attention is paid to the detailing at joints, the principal construction
phase of house building will give adequate airtightness. It is also helpful to indicate on construction details the
location of airtightness-critical items.