Airtight windows & doors

Forming a continuous airtight barrier around a building is critical to achieving a low energy or Passivhaus standard building. One of the areas of highest potential leakage can be at junctions between walls and windows.

Choose windows and doors with Class 4 airtightness

As 21° is dedicated to low energy and Passivhaus buildings, assuring high levels of airtightness of our windows and doors is a fundamental principle. Class 4 (BS EN 12207) is the best grade of airtightness for windows and doors. 21° triple glazed PERFORMANCE (GBS78)/ ULTRA (GBS98)/ windows are independently tested and third party certified to this exacting standard.

Double compression seal, as standard

One important design element for achieving high airtightness standards is the use of dual compression seals on all our window and door ranges as standard. This means that our windows and doors form an airtight seal in two locations, offering reliable long-term airtightness.

Compression not flipper seals

The type of airtight seal used is also important. 21° is committed to using compression seals (or gaskets) rather than ‘flipper’ seals because it believes that they offer reliable airtightness together with greater longevity and durability of the airtight seal.

Frame width and airtightness

In timber windows, dual compression seals inevitably result in slightly wider frames because of the extra space needed to ensure full compression.  The greater durability and reliability of the airtight seal more than compensates for the slightly wider frame.  In fact, this can be ‘worked around’ by ‘wrapping’ the window frame with insulation, as illustrated in the above diagram.