Despite widespread improvements throughout Europe in regulations affecting thermal insulation levels, designers of energy efficient buildings still have to deal with the problem of potential air leakage paths and thermal bridges. The high-performance criteria set by standards such as Passivhaus can therefore be difficult to achieve unless the right products are used.
With such a high proportion of heat lost through the roof, airtightness depends on a high standard of installation. With roof windows, for example, a lack of care is often taken with basic detailing such as cutting the underlay. In such situations, despite the fact that specialist tapes or sealants may have been specified by the architect, an air leakage test will quickly reveal poor performance if the wrong products have been used. Sadly, this happens all too often and with the rough and uneven surfaces in roof spaces the products soon fail. As a result, there is an increasing trend towards trying to ‘design out’ such problems, by adding features such as integral self-adhesive strips on underlays and air barriers, to seal laps and junctions with walls, chimneys etc.