# Structural Analysis of Factors Influencing the Costs of Facade System Implementation
## 2 Short Characteristic of Selected Facade Systems  
Aluminium-glass facades are one of the solutions dedicated to public, office, commercial, and service buildings [4]. Such buildings have become the objects of designers' architectural ideas, attracting designers with their form and original shape. The facade of the building should give the character of the object, as well as ensure comfort in its use. The facades are used to shape external walls, thanks to which curvilinear facades can be designed and made; these are characterized by lightness of form. The core of the facade is made of aluminium sections, while the filling is glass. The most frequently used systems are mullion-transom, semistructural, and structural systems [18]. Types of aluminium-glass facades are illustrated in Figure 1.  
The first type of structure consists of mullion-transom, and the inner space is filled with glass. On the outside of the mullion-transom system are termination bars and masking strips. A semistructural facade is smooth. Glass is fixed directly to the construction, and the gap is filled with a special weather silicone. The structural system is characterized by the possibility of obtaining an external glass faced without visible elements. This effect can be achieved by gluing the glass directly to the aluminium structure.  
The other facade system frequently used for public buildings in combination with aluminium and glass facades is a ventilated facade [18]. This solution is based on leaving a ventilation gap between the external cladding and the thermal insulation layer. A ventilated facade is defined as a set of elements for enclosing external walls, consisting of the following [2]:  
* external panels (for instance, cement, stone, wood-based, plastic, metal, or laminate) attached to the grate (suspended, glued, or screwed to the grate);
* grate (made of metal or wood) attached--suspended, glued, or screwed--to the external wall;
* fastening elements;
* insulating material.  
Due to the variety of materials used for the external panel and the substructure used (grate), it is possible to present the classification of ventilated facades, as shown in Figure 2.  
Figure 1: Type of aluminium–glass facades. Own study based on [26].  
Ventilated facades should meet all the requirements for technical assessment, and above all, should be tested for fire safety, namely, reaction to fire, resistance to fire, and ability to continuously smoulder [27]. Ventilated fire facade elements should be tested, and their fire class should be equal to class \"A\". Aluminium and steel grates, which are substructures of ventilated facades, are classified as non-combustible in class A1, and they are most often used for fire-rated ventilated facades. On the  
Figure 2: Classification of ventilated facades, according to the material of the external panel and the method of installation. Own study based on [8].  
other hand, the external lining itself, whether in the form of composite panels or HPL (High Pressure Laminate) panels, should have a fire-resistant core, which gives the fire-resistant characteristics to the element in question.