Abstract
<jats:p>When talking about improving the energy efficiency of the existing building stock, which also includes buildings that have been listed, it is necessary to bear in mind that it is obligatory to act according to the conditions prescribed for that area by the competent institution, and they are generally restrictive regarding any type of architectural and construction intervention. Generally speaking, they may not carry out any works, except conservation works. Such restrictive conditions often include elements of facade joinery (windows and doors), ranging from very rigorous (that the original appearance and original material must be kept), to more liberal ones that allow the replacement of old elements with new ones, which look true to the original, but the use of new materials is allowed. How to resist such architectural challenges is the leitmotif of this work. The work does not intend to solve this problem, but rather to indicate potential challenges and possibilities of overcoming them.</jats:p>