EXTERNAL WALLS

STONE
Natural stones represent a constant presence in architecture. The use of stone materials in buildings has been for a long time the exclusive prerogative of works for important buildings, such as churches or public buildings.
The natural stones commonly used in construction are obtained by extraction from the different types of rock existing in the depths of the earth’s crust. There is an indissoluble and precise link between the area belonging to the building and the stone material used. The stone material mainly available on site, in fact, has influenced constructional typologies and formal languages in different historical phases. This results from the fact that the distribution of superficial lithoid materials is not homogeneous and the surface areas are characterized by differentiated soil compositions with the presence of specific stone species.
The development of the use of stone materials as non-structural vestments has been accompanied by the evolution of the techniques of processing in septic layer, also in combination with supporting materials of different nature.

The commercial classification in the field of construction relates to the codification of the standard UNI 8458 materials that identifies four classes of stone materials.

1. marble: polished rocks of easy workability and medium hardness, around 3-4 of the Mohs scale. These materials are mainly used for decorative purposes and for this reason the morphological characteristics assume relevance. In this regard, it is important to carefully evaluate the differences in colour, texture, crumbling and grain, as well as any imperfections present in the original material. The characteristics of compactness, low absorption make the metamorphic marbles suitable for outdoor applications. However, the performance characteristics must be evaluated, generally lower than those of granites;

2. granites: more mechanically resistant polishing rocks with a characteristic granular appearance, with a compact structure, characterized by high hardness of the order of 6-7 of the Mohs scale. For excellent performance they are suitable for outdoor applications for flooring and coatings; thanks to their compact and resistant structure they are able to effectively withstand the action of atmospheric agents, pollution and even intense stresses;

3. non-polishable stones: stones of geological origin with varied characteristics, hard or tender, of different colors and performance characteristics. Depending on the consistency they are commonly divided into tender and hard. Among the most common soft rocks we find those with a calcareous binder, tufa and sandstone, all characterized by good workability and not high curability. Hard rocks, however, include trachyte, porphyry, basaltic, quartzite, slate, gneiss;

4. travertine: soft and porous stones of sedimentary origin, easily machinable, recomposed for chemical deposit with calcareous binder. The high presence of vacuity is due to the decomposition of the fossilized interlocking organic components, animal or vegetable, which testify the lake origin. Its characteristics make travertine a material that is easy to use. Despite having limited mechanical properties and porous structure, it is sufficiently resistant and durable for use in construction, as long as it is in suitable thicknesses. Just extracted, it has a tender and almost spongy structure, which subsequently acquires greater compactness. Some types can be polished.

METAL STRUCTURE
There are numerous metal alloys used or usable in construction based on iron, copper, aluminum or zinc.
Steel alloys for construction are characterized by excellent mechanical strength and high elasticity and ductility. Its elasticity and ductility make it the ideal material for seismic constructions, although in some cases the extreme elasticity can become a problem that needs to be compensated by specific stiffening measures (increased profile, bracing, composite profiles, collaborating elements).

The typical characteristics of steel structures are:

TYPES OF METAL STRUCTURE
In the «civil» context, that is, in medium/small buildings such as houses, offices, premises, we can distinguish three main types of structures:

Structures with light profile
They are structures realized with the same philosophy of the traditional structures to wooden loom. The basic profiles are made of thin sheet metal, very similar to those used for plasterboard. Uprights and sleepers are positioned in everything as in typical wooden houses as it is an evolution of the same technique. This typology is widespread in the northern European and Anglo-Saxon countries where the culture of the light chassis house is still present.

Structures with UNI profile
They are the most common and mainly use UNI profiles (the so-called «putrelle»), easy to find and work. They are very versatile as they exist in a wide range of sizes and can therefore cover even quite important lights without special workings or constructions.
They are easy to weld so they lend themselves to the creation of bolted joints for a fast and robust installation. The high weldability of these profiles also allows the realization of special and exclusive pieces, customized for the structure without special surcharges. If the structure is protected from moisture and condensation does not need special treatments, if instead it has visible portions or there is the risk of infiltration or stagnation of moisture, the technician must assess the correct treatment of the surface, depending on the exposure and the condition in which the element is located (usually galvanizing for the outside and painting for the inside). In this case, the finish is completely free, the plugging can be made either with dry technique as in the first case, or wet (brick walls, gasbeton, or concrete).

Structures with composite profile
Composite profiles are all those types of structural elements composed of several elements that would be standard in themselves but which, assembled together, create an element with particular mechanical performance. The best known example is the reticular beam that, obtained by assembling simple profiles according to a precise design, allows to obtain very light and extremely rigid structural elements. This type of structure is obviously more expensive as it requires a greater workmanship in the prefabrication phase than the use of a simple «putrella», however the mechanical performances that can be obtained are exceptional, obtaining free lights over 10 meters with relatively light structural elements.

CONCRETE
Mixing the cement powder with the water you get the cement paste, which can be combined with sand to obtain the mortar, suitable for the realization of funds, light masonry, screed and plaster, or with gravel of different sizes to have concrete.
The concrete itself, if reinforced inside with steel rods, becomes concrete or reinforced concrete, a building material of great use in the world of construction, especially for its strength to compression (given by cement) and elasticity (given by steel). Thanks to these mechanical characteristics, concrete, in particular reinforced concrete, is used for foundations and supporting structures such as beams and pillars.

BRICK
The bricks include a variety of materials originally created with purified clay baked in special kilns and, only in more recent times, also with the use of cement and sand; in addition to brick, full or drilled, there are other building bricks such as pots and tiles. It is a construction system that defines a vertical closing structure of a building organism, consisting of basic elements superimposed on each other, arranged according to one or more warps or rows and, in modern characters, made integral with each other by binding materials. The masonry can be built dry, as in ancient times, or made monolithic by mortars (lime, cement, plaster, etc.). The masonry was created to fulfil the function of a closing element and protection of indoor environments (such as walls), to withstand the static loads and thrusts that weigh on it (as a supporting structure), to define the finish of the building envelope (as a cladding). The masonry, according to the different materials that constitute it, has different performance behaviours (fire behavior, thermal and acoustic insulation, thermal inertia, mechanical resistance, etc.). The masonry works are regulated by UNI 9124 since 1987, for the execution technique and construction.

WOOD
The wood is one of the most ancient material for the construction of the buildings. It can be used in different form and modes depending on the physical properties of the original wood.
In the construction world, the structural wood is prevalent – that is, beams or boards of wood glued, wedged or screwed together, used as load-bearing elements. Alternatively, wood can be used in slats or boards for frames and coverings.
The main defect of the wood is its burning, for this it must be used with care in a building project, or it can be improved by using fire-retardant treatments.

Xlam
The Xlam structure is a massive technique that involves the use of load-bearing elements consisting of multilayer panels, very often in coniferous wood, whose static behavior is similar to that of slabs. A panel is obtained by crossing and gluing layers usually between 15 and 30 mm thick.
The most popular panels have dimensions of 3 meters in height and lengths up to 16 meters, with a thick average of about 50 cm. Xlam panels are load-bearing and can compose both perimeter and partition walls. The structural performances are very good, they easily resist to heavy loads and external stresses (also seismic).

Structure Block House
The Block House technique, among the first used, is a massive solution and involves the overlapping of heavy wooden elements, once the logs, between them wedged. The Block House system is part of the tradition of central-northern Europe and North America and has been perfected over the years to solve problems of air and water infiltration.

Frame system
The frame construction system is a lightweight solution that involves the construction of a supporting skeleton with non-bearing buffers. Even this technology has ancient origins and the system of beams and pillars works like a frame of any other material, although it requires a careful design of vertical and horizontal bracing. Beams and pillars are made of solid wood or laminated wood and their dimensions vary according to the lights to be covered and the loads to be supported; on the size of the pillars, moreover, their height also affects a lot. The buffers can then be positioned outside the structure, reducing the thermal bridges, or in light to the pillars, creating situations of discontinuity but working as counter winds.

Platform Frame and Baloon Frame systems
The Platfrom Frame construction system, a special frame structure born in Northern Europe and now widespread also in the United States, allows the construction of buildings up to 4 floors in a short period of time. The load-bearing walls consist of wooden joists at regular intervals, closed by rigid panels based on wood or plaster. The wheelbase of the vertical uprights is now defined by the standard dimensions of the panels and is very often 62.5 cm.
The walls can be entirely or partially prefabricated, accelerating the construction time and saving the manufacturing. The uprights hold vertical loads and the structure itself is rigid as it consists basically of slabs that cooperate with each other.