The windows and doors structures and their performance characteristics prescribed by European
directives and determined by the new product standards play an important role in the energy balance
of buildings. Between the performance features we find the air tightness of windows, which limit
value required by a certain usage must be assured in the moment of installation. This research intends
to investigate the influence of structural elements on windows and doors performance. The present
article describes the role and effect of sealing’s on windows air tightness. A series of laboratory
experiments were performed examining the influence of primary and secondary weather-strips as
well as the effect of sealing’s weathering on elasticity. By removing the primary weather-strip the air
tightness declined significantly at each pressure level. Opposite to this the secondary weather-strip
elimination doesn’t affected considerably the air tightness at certain pressure levels. The impact of
primary sealing weathering varied among the examined window types