Press Information
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| Issued: November 2008 |
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Over and Above
Over-cladding has fast become a popular choice for renovating the exterior of existing buildings. Offering a cost effective solution that gives buildings a ‘new lease of life’, over-cladding is most commonly used with high-rise structures, where the alternative of demolition followed by a new build project can be both expensive and time consuming. William Harwood, director, T.I. Dynamic Facades discusses the drivers behind the rising trend in over-cladding, and highlights some of the key challenges when considering this refurbishment technique.
The first factor to review when considering over-cladding a structure is whether the existing exterior will withstand the loading imposed by an additional construction. This is broadly composed of two parts. Firstly the weight of the proposed over-clad system must be evaluated and confirmed whether it is within the calculated load bearing capacity of the building. Secondly, the integrity of the structure must be assessed, as it is this to which the new exterior will be fixed.
These first two points will qualify whether over-cladding is a viable option for a specific project. However, in addition to these, system depth must also be considered. For example, windows and balconies will often determine the maximum overall depth that can be achieved with the new exterior envelope.
Minimum Depth Maximum Impact
Early over-cladding projects tended to favour the use of insulated render systems, because their lightweight construction minimises the strain on a structure. Moreover, the overall depth of an insulated render system is often much shallower than traditional cladding systems such as terracotta rainscreens and stone façades.
As projects are increasingly driven by aesthetics, façade innovators have developed cladding solutions that minimise system depth, whilst simultaneously maximising the design impact that can be achieved.
When tackling over-cladding, the developer should consider the thickness of the tile as well as the depth required for a carrier framework. Some advanced ‘clinch’ carrier systems have been specifically designed for the over-cladding of structures. Engineered to deliver a tight construction, these clinch rails help deliver a high quality exterior finish whilst minimising overall system depth. With new build cladding projects this maximises the available internal floor space, but where over-cladding is concerned, it facilitates use on buildings where the window recess depths are limited.
Where finishes are concerned, over-cladding has historically been extremely restricted over the types of materials that can be used. This is because the thickness of many popular natural finishes, such as terracotta and stone, has caused the overall system depth to fall outside of project parameters. Again, recent developments in façade technology have seen the launch of natural materials that are manufactured to be much thinner and lighter than traditional alternatives, and can also be used with the clinch rail to provide minimal construction depth.
Final Finishes
Many structures that are considered for over-cladding consist of concrete infills and spandrel panels. These are ideal from a build perspective, as they can often withstand high loads and the construction weathers well over time. However, the final finish of these economical constructions now appears outdated against more modern city landscapes. As such, when planning the regeneration of high-rise concrete buildings, aesthetics have become as important as practicality. This has led viable buildings to be demolished in the past because architectural visions could not be realised using traditional over-cladding techniques.
Following the recent innovations in façade technology, it is anticipated that design-driven demolition will be prevented, as the new systems being launched are lightweight and available in a wide range of finishes. For example, the development of a thinner and lighter single skin terracotta rainscreen product now makes it a practical and cost effective option for over-cladding. Previously, terracotta rainscreens needed a twin skin tile construction in order to deliver the required performance, which made the tiles too thick for use on many over-cladding projects.
Stone has also been re-engineered so that it can cost effectively overcome the practical constraints of an over-cladding project. While traditional stone façades had to be approximately 40mm thick, lighter weight systems have been developed that can be manufactured to between 6mm and 15mm thick.
System strength is achieved by bonding the stone facing to a reinforced backing, such as fibreglass, aluminium or aluminium honeycomb. By making the system lighter weight and much thinner, stone for the first time can be considered as a viable option when over-cladding.
When approaching the regeneration of high-rise areas, developers have two choices – demolition or renovation. For the cladding industry, the wider choice of finishes that are now available, as well as the practical advantages that these are proven to deliver, means cladding renovation can now be fully considered as a cost effective option and at the same time achieve a high quality finish to rival even the most premium of new builds.
