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Thermal and acoustic insulation enhances a building's protection, so the construction arrangement involving a ventilated façade is very often used. Familiarity with the technique is essential for its correct application. The following are its key points.
This name is used to refer to all those façades made up of an outer layer of cladding with an inner one for support, with the two being separated by a ventilated air-space. There are three separate parts to a ventilated façade, namely, support, space and cladding.
The support is the inner face on the façade and it is what gives it its strength, being required to absorb wind stresses and distribute the effect of gravity on the structure. It should therefore be made of a mechanically resistant material, such as brick, concrete blocks or a wall of reinforced concrete. It is not advisable to build this support with double hollow brickwork, as this is not capable of distributing the gravitational pull the stones have on the structure.
The support may also involve a metallic structure, with attachment almost always made of a system of guides that are bolted or welded to it.
The space is the gap between the support and the cladding. This space may be divided into two parts; one being the actual ventilated space itself and the other the insulating material that may be fitted, such as polyurethane, or insulation in panels, such as extruded polyurethane or rock wool.
In order to ensure the space is suitably ventilated, the gap should be no less than 2 cm, but considering detachments and construction allowances we recommend 4 cm. We should insist upon this point, as this space is going to have a chimney effect on the building, drawing the air up from below and keeping both the insulation and the cladding dry. Ventilation holes should take up at least 50 cm2 per linear metre of façade.
The cladding will involve the natural stone that more closely meets the technical specifications expected of it. It should be fitted in a way that allows for the free movement of its components, which may be panels, boards or slabs of different materials, with their attachment to the support involving other items, anchors, in order to guarantee their stability. It should be ensured that all the forces acting upon the stone are transmitted to the support solely by means of the anchors.
The attachment between the cladding and the anchors may involve pins or pegs that are inserted in the hole provided accordingly in the stones. Each anchor has a through-tenon that will fit into two stone pieces at the same time. In order to allow for their unrestricted movement, the pin will only be set into one, in other words: the pin is set into one stone with cement or resin and the other stone will be fitted with a plastic lug for simply holding the pin.
There are two types of anchors depending on their structural role: those that are load-bearing or for lift, withstanding both the weight of the stone and wind stresses, and those for holding or attachment that only withstand wind stresses and stop the stones from tilting.
Depending on the type of attachment to the support, there are three kinds of anchors:
Mortar anchors
Anchors for embedding in concrete or brickwork with mortar or resin. They are fitted by making a hole in the support and inserting mortar in a proportion of 1:3; the anchor is then inserted and can be adjusted whilst the mortar is still fresh. Once the mortar has set, no further adjustment is possible. The same anchor may be used for positioning in both the vertical and horizontal joints between the stones, as these anchors tend to be cylindrical in shape and have the same moment of inertia in any position.
Anchors to be fitted with a wall plug
These anchors are fitted into the support: brick, concrete or block, using the appropriate plug in each case.
Anchors on auxiliary sections
This range of anchors involves the fitting of an auxiliary substructure made up of vertical sections to which the anchors are attached. These sections are attached to the concrete structure and are braced against the wall in order absorb wind stresses. The section is notched to avoid any possible movement of the anchors. This system allows for gaps with the wall of between 50 and 300 mm. This system is designed for large-sized stones.
This article has been written by Eduardo Y谩ñez, head of the technical office at the firm Halfen-Deha.
Photos courtesy of Halfen-Deha .
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