Aluminum for ventilated facade
Each hinged ventilated facade usually includes, least, the following components (figure 1):
- substructure - supporting frame for cladding panels;
- mounting brackets to the wall subsystem, on which the ventilated facade is installed;
- fasteners - screws, screws, dowel, rivets for fastening elements with each other substructure, substructure - the wall, facing panels - to the substructure;
2 - outside
3 - insulation
4 - a vapor-permeable barrier
5 - the fastening element
6 - the fastening element
7 - substructure
8 - the gap
9 – ventilation cavity (gap)
10 - exterior cladding
11 - bearing wall
12 - thermorupture
13 – anchor
Figure 1 - Arrangement of a hinged ventilated facade (according to DIN 18516-1)
The essence of a ventilated facade
The essence of a ventilated facade is, that the insulation and vapor-permeable barrier, one side, and an outer cladding, on the other hand, structurally separated ventilated gap. This ventilation cavity between the façade components regulates the humidity inside the building: all moisture is reliably removed through the ventilated gap. Wet the outside of the bearing wall dries very quickly. All this ensures an optimum climate inside the building.
Figure 2 - The principle of the ventilated facade
Subconstruction or subsystem?
The term "substructure" coincides with the English term «substructure» and «Unterkonstruktion» German term, which is used in international regulations for ventilated facades. At the same time, in the English-language technical literature often used such terms, как «supporting structure», «support system», «subframe» и «base frame». In the Russian-speaking environment specialists in curtain walls instead of the term "substructure" is often the term "subsystem" is used, and the term "supporting framework".
Materials for the substructure of ventilated facades
The international authority for ventilated facades - DIN 18516-1 – establishes requirements for the materials of ventilated facades, which can be used without special confirmation of their corrosion resistance, including, for:
- cladding panels,
- and the substructure
For the manufacture of substructures, in particular, recommended:
- corrosion-resistant steels;
- aluminum alloys;
- copper alloys;
- thick structural steel least 3 mm with a corrosion protection paint coat.
The use of other materials of substructures, for example, wood, It requires special acknowledgment and resolution.
Aluminum alloys for substructures
For aluminum substructure it is recommended to use aluminum alloys, are listed in the European Standard EN 1999-1-1 (Eurocodes 9 "Design of aluminum structures"). Typically, aluminum alloys are used for the substructure of ventilated facades 6060 and 6063 in states T6 and T66.
Aluminum substructure of a ventilated facade
The aluminum substructure ventilated facades is made up of aluminum profiles and anchors, as well as various fasteners (screws, screws, rivets), which form a frame for mounting cladding panels on the outer or inner wall of new or existing buildings.
Consider the requirements for aluminum substructure of a ventilated facade in the famous example of the substructure of a ventilated curtain wall Hilti EuroFox, which is widely used throughout the EU territory. Below are the specifications of the aluminum substructure of a ventilated facade of the certificate, which gives the right to use it under normal climatic conditions across the UK territory, from Wales to Scotland and Northern Ireland.
Material aluminum brackets and guide
The Hilti EuroFox aluminum subsystem includes:
- aluminum brackets of various shapes and sizes;
- aluminum guides (profiles) of various shapes.
All aluminum components subsystems are made of aluminum alloy 6063-T66. Note, the minimum strength of an alloy of aluminum profiles 6063 T66 is able to 245 MPa. T66 indicates the state, such that to achieve high strength in the production profiles were taken special measures. These measures may, for example, It consists in the tight control of the initial billet temperature, temperature profile at the outlet from the die and the rapid cooling profile on the press.
Protection against corrosion of aluminum substructure
No special measures to protect the surface of the aluminum components provided by the substructure. At the same time, in conditions of high humidity reacting the unprotected aluminum with the cement-based materials leads to its severe corrosion. Therefore aluminum brackets when installed on concrete and brick wall must necessarily have a backing of polypropylene or polyvinyl chloride.
stainless steel fasteners
Guiding aluminum profiles are connected to aluminum brackets using self-tapping screws (self-tapping screws) 5.5x19 mm from corrosion-resistant austenitic (stainless) steels EN 1.4567 (AISI 304) и EN 1.4578 (AISI 316). These screws labeled A2 and A4, respectively. These are analogues of austenitic stainless steels and 08H18N10 08H18N10M2.
Figure 3 - Self-tapping screws of corrosion-resistant austenitic steel for connection of aluminum profiles with aluminum brackets
Ancillary components of the aluminum subsystem include:
- fixing screws - self-tapping screws (self-tapping screws) made of corrosion-resistant steel or heat-hardened steel for fixing the brackets to the load-bearing wall;
- special anchors, consisting of a polyamide sleeve and special screw of galvanized steel or stainless steel. These anchors are used for fixing the subsystem to a concrete or brick retaining wall.
Figure 4 - Vertical and horizontal mounting rails
Load from the subsystem to the supporting wall
Aluminum subsystem Hilti EuroFox used in the construction of ventilated facades as the supporting structure for facing external or internal walls of new and existing buildings. It is designed for the efficient transmission of the wind load and the weight of the lining to the carrier, concrete or brick, walls.
Thermal insulation lining the brackets
Limit the wind load on the wall with mounted ventilated facade must be calculated in accordance with national standards. In Great Britain, for example, limiting wind load computed according to Eurocode 9 (EN 1991-1-4), but the final appointment of marginal wind load multiplying factor used 1,5.
The number of brackets, whereby aluminum subsystem is attached to the supporting wall, It should depend on the weight of the selected type of lining and determined at the stage of designing a ventilated facade. Details of brackets and their strength design shown in Figure 4. The design load at the fixing between the various components of aluminum subsystem should be lower, than their calculated strength.
The design of the guide profiles and a method of attaching them to the brackets shall meet the requirements of national building codes, subject to the minimum the mechanical properties of aluminum alloys used in their predetermined state, for example, 6063-T66 or 6060-T66. The maximum deflection of guides (aluminum profiles) between two supports should be more than one two hundredth of the span length (L / 200), and for cantilever elements - one hundred and fiftieth of their length (L / 150).
Usually, aluminum profiles subsystem is fixedly secured in the middle of their length with the use of conventional circular holes. At this point the remaining fastening profiles operate sliding on the elongated holes, which allows the profiles to lengthen or shorten with temperature changes (see. Figure 4).
Figure 6 - Aluminum guide profiles
To ensure the free thermal expansion is necessary to ensure the long gap 2,5 mm per meter of length. For standard guide length 3 m bandgap 8 mm between adjacent rails is considered sufficient. When calculating the thermal expansion coefficient of aluminum generally take 23h10-6 1/TO. It means, what, for example, temperature difference in 100 degrees Kelvin (or Celsius) each meter of the aluminum profile will change its length by 2,3 mm.
Fire resistance of an aluminum subsystem
aluminum brackets, guides and fastening them together are non-combustible. Therefore we can assume, that the British construction standards they have class 0 or "low risk".
Aluminum brackets subsystems include pads made of polyurethane or PVC for, to reduce the risk of "cold bridges" through the contact bracket-wall. As these brackets largely "hidden" behind the facing panels and, Moreover, present in relatively small amounts, they are unlikely to have a significant impact on the overall fire facade cladding.
At the same time, for each system with ventilated facade necessarily draw conclusions about its fire is based on tests, which conducts special accredited laboratory.
Drainage and ventilation
The minimum width of the ventilation gap between the back wall of the cladding panels and the insulation or wall (in the absence of insulation) depends on the height of the building and the climatic features of the area, in which the facade is set. Hilti Eurofox system has a ventilation gap of at least 38 mm for facing panels with plugged or labyrinth joints and 50 mm - for open joints.
Aluminum substructure itself does not require any maintenance. At the same time, the whole system of ventilated facades must be inspected annually, To make sure, that the internal elements of the facade are in order and well ventilated, and cladding panels are in place and properly secured.
The service life of the aluminum substructure
Aluminum subsystem Hilti Eurofox in normal climatic conditions, the UK is designed to limit the service life of not less than 35 years.
Protection against corrosion of aluminum building constructions
Note, that the normal conditions in the various regions of the UK are significantly different from each other, for example, by annual precipitation (figure 7).
Figure 7 - The annual rainfall in Europe and neighboring regions
Can be seen, that rainfall in the European part of Russia, as well as Ukraine and Belarus is 500-800 mm, what in 2-2,5 times less than, than half of the UK regions.
This circumstance is taken into account, to varying degrees,, when assigning protection of aluminum building structures against corrosion as in domestic building codes, and in the latest European construction standards for aluminum structures EN 1999 (Eurocode 9).
- Therefore, in dry and normal regions may allow for use in building constructions unprotected aluminum even in a polluted urban atmosphere.
- On the other hand, in humid regions, as well as in coastal areas, aluminum may require corrosion protection even in pollution-free (rural) areas.
1) Certificate ventilated facade HILTI EUROFOX, 2013
2) Sustainable refurbishment of exterior walls and building facades, Final report, Part A, 2012