October 2008
A New Lease of Life
Widely accepted as a cost effective and efficient method of renovating a building, over-cladding enables a high quality exterior envelope to be provided while retaining the existing structure. William Harwood, director, T.I. Dynamic Facades, discusses key considerations in relation to this renovation technique and explains how recent advances in façade technology have broadened the choice of finishes that can be used when refreshing a structural exterior.
Architectural trends in the 1970s led to a steep increase in the number of high-rise buildings being constructed across the residential and commercial sectors. As concrete infill and spandrel panels were the most economical and efficient materials to install at the time, these were commonly used to erect the high-rise structures.
However, the advancement of building methods over recent years has facilitated the use of more stylish and aesthetic finishes and materials, resulting in the grey constructions of the 1970s appearing increasingly outdated against the modern city landscapes.
When approaching the regeneration of high-rise areas, developers have two choices – demolition or renovation. When the renovation route is selected, careful consideration is required regarding the compatibility of materials with the existing structure.
Considering Cladding
Historically, insulated render systems have been most commonly used for over-cladding. This is because their lightweight construction minimises the strain placed on a structure.
While system weight is a critical consideration for over-cladding, of equal importance is the integrity of the existing structure. This must be able to withstand the additional weight of a new exterior envelope, and if not, over-cladding cannot be used.
Once these factors have been assessed, and it is confirmed that the existing structure will deliver the required load bearing capacity, the next key consideration is the limitations on system depths. For example, windows and balconies will often determine the maximum overall system depth that can be achieved.
Modern Choices
Where an existing structure is sound, it makes commercial sense to change the façade appearance, rather than demolish a building. However, restrictions over the type of cladding that can be used, because of system weight and depth has, in the past, led some viable buildings to be demolished and replaced with a brand new structure.
Following a number of recent innovations in façade technology, it is anticipated that design-driven demolition will be prevented, as new systems have been launched that are lightweight and available in a wide range of finishes. This includes natural materials such as terracotta and stone, which have historically been too heavy to use as an over-clad on many existing developments.
Think Terracotta
Terracotta has long been a favourite natural façade finish, owing to its ability to blend in with surrounding brick and mortar constructions. While early terracotta cladding systems used a twin skin tile, the development of a thinner and lighter single skin product now makes it a practical and cost effective option for over-cladding.
In fact, the most advanced single skin systems weigh an average of 10kg per square metre less than traditional offerings, achieving strength and durability through an innovative manufacturing process rather than thickness. A porcelain base baked at a high temperature significantly reduces the water absorbency of the system, making it more resistant to the freeze/thaw phenomenon that causes some silicon sprayed alternatives to fail.
Stylish Stone
In the same way that terracotta has been engineered to be suitable for over-cladding, advances with stone façades have also been made.
Although stone is naturally a durable material, to deliver the required performance levels and provide a viable exterior finish, stone façades have traditionally had to be approximately 40mm thick. However, lighter weight systems have been launched to market 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 cost effectively overcome the practical constraints of an over-cladding project.
The renovation of high-rise structures remains a popular method for the regeneration of existing developments. However, the availability of a wider choice of high quality and lightweight façade systems facilitates greater flexibility in design, that will ultimately allow the creation of bright and modern skylines, where grey towers once stood.