The concept and the history of building ventilated façades are not novel. Actually, the first examples of building façades are found in medieval Europe. Wood was the dominant material for constructing façades since it was easily sourced from the vast forests in Western Europe during this historical period.
If we try to find a benchmark project in a contemporary building, we could arrive at no other than the Flatiron Building in New York, since it uses a metal structure and cladding. A significant parameter for the design of Flatiron has been the revision of the New York Building Act in 1892, which abrogated the requirement for masonry on the grounds of fire safety reasons and gave rise to the formation of plenty of modern building methods. Namely, the creation of a shell, which is suspended through a secondary level of support system on the primary frame of the building.
In the case of the Flatiron Building, glazed ceramic panels are the dominant cladding material of the fa̤ades. Today, the usage of ventilated fa̤ades with the simultaneous integration of a multitude of different materials Рnatural and artificial, such as metal, glass, ceramics, concrete, composite wood, plastics, etc., has prevailed worldwide.
Naturally, progress in the field of materials science has been an important factor in the realisation of modern buildings.
The ventilated façade is synonymous with the structure of a multi-layered shell. A key feature of the ventilated façade is the clear separation of structural elements that are in direct contact with the interior or exterior space, as follows:
- External cladding
- Air gap
- External insulation
- Internal masonry
The creation of an air gap throughout the height of the building, in which the circulation of air remains unobstructed, but at a higher temperature than that of the natural environment, implies the circulation of air in conditions of natural attraction. Briefly, the air enters the gap, is further heated by the absorbed solar radiation and is emitted by the cladding, moves upwards, creates a vacuum, which tends to be filled again with air and hence continuous ventilation is ensured within the shell.
Results of external thermal insulation and natural ventilation can be summarised as follows:
- Improving thermal comfort in the interior of the building.
- Saving energy for both heating and cooling, through the reduction of thermal losses.
- Protection against moisture, as the external cladding is a first protective level, while at the same time, ventilation accelerates the removal of residual moisture.
The three axes for the sustainability of buildings are as below:
- Limitation of the environmental footprint (Construction – Usage)
- Ensuring the optimum operation of the building over time.
- Enhancing the comfort levels for its users.
The Fireproofing Principle Of The Ventilated Façade As A Fire Transmitting Factor
The fundamental operating principle of the ventilated façade is at the same time its weakest point in terms of fire transmission. The natural attraction of the air within the façade dramatically accelerates the vertical fire spread of fire, consequently facilitating its expansion throughout the building. In this way, even a small localised fire can potentially evolve into a large-scale fire in the whole building.
Grenfell Tower in London has been the most notable case of a building fire for several decades. A residential building of 24 floors, initially erected in 1967 and renovated in 2015-2016 with ventilated façades clad with LDPE Aluminium Composite Panels and insulated with PIR. The non-compliance with the Fire Regulations Act was considered the root cause of the tragic death of 72 people.
Vertical fire expansion in the 24-storey building. It is worth noting that while the building seems mostly unharmed, there is a vertical fire across the entire side of the building with possible disastrous effects.
Tackling Design Methods (Fire-Barriers And Fire Compartmentalisation)
It is possible to maintain the advantages offered by ventilated façades while ensuring fire protection. The placement of fire barriers horizontally and vertically in order to fire compartmentalise the façade in accordance with the General Fire Safety of the building answers the existing challenge.
A fire barrier is placed horizontally with fire-resistance sealing tape, leaving a gap of 25-50 mm from the surface of the cladding. In this way, the ventilation of the façade is ensured while it is interrupted in the case of fire.
- Complete vertical fire barrier (compressed Rockwool in aluminium shell.
- «Open» horizontal fire barrier with fire-resistant sealing tape.
- Fire-inflatable sealing tape.
Example of Façade Engineering Study as above. In this case, and in the particular Unitized System with embedded brick slips, we can see the vertical fire-barriers at the side of the unitized module and two vertical fire barriers with the fire-inflatable membrane.
Re-Defining The Proper Function Of Façade In Existing Buildings:
Case study with a residential complex in Stratford, London, built in 2006-2007. In 2021, it joined a State Funding Program in order to harmonise with the Fire Protection Regulation. The Grenfell building tragedy has triggered the imperative to carry out checks regarding the safety of buildings in Great Britain.
The range of interventions required is extensive, both in terms of replacing the materials of the façades with fire-resistant ones, as well as in redesigning the shell by creating fire compartments. The materials replaced are:
- Aluminium Composite Panels with 3mm Solid Aluminium Sheets.
- Wood cladding sheets with fibrocement sheets.
- Wooden decking floors with aluminium ones.
- External thermal insulation system with corresponding non-flammable material.
- Spandrel glass curtain panels with a non-flammable core.
- Brick slip cladding due to the absence of fire compartmentalisation.
View of an existing gap within the shell. The lack of fire barriers, combined with the presence of flammable building materials, creates the conditions for the rapid spread of fire vertically (chimney effect).
Need to incorporate principles of fire protection of ventilated façades in the Architectural Design and Engineering study
The requirements in the building construction sector follow a steadily increasing trend:
- Architectural work tends to become more complex (Design & Build).
- Building systems and materials are becoming more specialised and sophisticated.
- The sustainability of the building has been widely recognised as a critical parameter.
- Building specifications are becoming stricter.
- The regulation framework becomes wider in scope and more complex.
- The number of stakeholders in the project implementation is increasing, and new specialities appear.
In this context, there is a need to incorporate the fire protection principles of the building envelope from the initial design stages.
The perfection of the construction cannot be simply achieved by adhering to regulations. On the contrary, the principles served by the latter should become an integral part of the architectural composition.
