Cladding – huh – what is it good for…?
Too many buildings are constructed and decorated in a time warp, with scant consideration for the realities of weathering, ageing or wear and tear. DR HILARY DAVIES presents some tips for improving building longevity.
Is it possible to construct a building that looks as good after 10 years as it did when new? Surely we shouldn’t have buildings that are barely a year old showing ugly staining of their façade. The Melbourne Recital Centre at Southbank (see photos right and below), officially opened in February 2009, won the National Award for Public Buildings at the 2009 Property Council of Australia Rider Levett Bucknall Awards for Innovation and Excellence. Yet, one year on, the black composite cladding already has signs of weather-related staining, blotchy white cobwebs at many of the joints, and the beginnings of streaky discolouration.
I think all designers and architects should undertake a course in maintenance and building defects. Maybe, just maybe, we then would have buildings that stand the test of time. Many building managers are being forced to renovate or renew external cladding after just one or two years. What a hopeless expense and an unnecessary imposition on tenants and landlords alike.
Cladding is a costly and critical element of buildings. It has three functions – to look good, to keep out the weather and to transfer any dynamic wind loads to the structure. They tend to be interrelated. If the ‘weather’ in the form of rain, wind or humidity gets behind or into the cladding façade, it can lead to a range of problems – and then the aesthetic function is usually compromised or, worse, fixings fail through corrosion or fatigue, leading to cladding detachment. A further common problem is joint detailing failures that allow wind or rain penetration and consequent deterioration of the internal environment.
It only takes a basic understanding of materials science (and a degree of common sense) to think about some of the requirements for successful cladding assemblies to avoid the excessive cleaning bills or even the enormous costs of early replacement of façades.
CLEAN, REPAIR REPLACE
The mantra that was instilled into me when learning the basics of building maintenance was: ‘Can it be cleaned? Can it be repaired? Can it be replaced?’ An essential adjunct to this was ease of access. Maybe I look at buildings with a different eye, but I often look for the attachments for cleaning cradles. Then again, perhaps this isn’t such an essential feature – I remember articles in the newspaper in Hong Kong extolling abseiling cleaners. Some of the complex façades created with overhangs (I’m thinking here of Hong Kong’s Lippo Building, in particular) do not really allow for cleaning from cradles, and I also remember window cleaners coming to my office, attaching a hook to an eye bolted into the ceiling and swinging outside the window on a harness. Not perhaps usual practice in Australia (but at least they had thought of cleaning needs and built in hooks – unless of course this was a retrofit!).
There are, however, some new developments in glass cleaning technology that may warrant investigation. There are hydrophobic or hydrophilic films that make glass self-cleaning. The online portal GlassOnWeb gives some links to glass manufacturers’ products and some details on the technology1. And Iku Windows2 has developed a cleaning system integrated into the façade, so that water and detergent are dispensed and wipers clean the façade automatically – essential if you have any building-integrated photovoltaics that need to be clean for better solar performance.
Maintaining appearance is vital for any façade. Some materials naturally weather better than others. Brick rarely needs cleaning and seems to improve with age, but stone and concrete will generate staining patterns related to uneven rain washing of dirt deposited from pollution. Corners of buildings will get less exposure, as will the underside of any sills or projections, and consequently they may be susceptible to more staining. Yes, buildings can be cleaned, but the costs of scaffolding may prove excessive if there is a high frequency of cleaning, and careful choice of chemicals is needed, otherwise this can generate more problems.
For example, aluminium gets pitted over time, especially in a marine environment. One method for cleaning is with highly reactive and toxic hydrofluoric acid – it requires care, and not just for the users. For instance, during cleaning of the BBC headquarters in London, some spray etched the BMW cars parked on the podium! Excessive use of water to wash buildings of their grime can lead to moisture penetration and then corrosion of fixings. Washing or even just rain can set off efflorescence on both the surface of permeable materials or at joints, causing more staining from salt crystallisation. But maybe we won’t need to clean buildings of the future. How about self-cleaning metal façades3, or self-cleaning tiles with a titanium dioxide coating4, or self-cleaning coatings for masonry that are guaranteed for 15 years5? Cleaning could become so much simpler.
Deficient fixing detailing is probably the most serious of the problems with cladding. The fact that these fixings are usually hidden makes inspection difficult (and often impractical), and defects may only be revealed catastrophically. What is often not properly accounted for in joints is the daily and seasonal thermal and moisture movement of materials. Heavy cladding materials like stone and concrete have a natural inbuilt tying-in effect from their own weight. Not so for thin composites. These are lightweight and, if dark and insulated, will absorb heat concentrated into the surface and expand. The effects create cracking and spalling, especially at corners where the movements are less restricted.
So are there any messages here? The usual one is to get the FM involved in the design, so that cleaning, maintenance and repair are considered at the design stage. Maybe we should be avoiding complex façades that make cleaning difficult, and pay more attention to basic physics and chemistry – and appreciate their impact on building materials’ movement and deterioration. There are too many ‘design focused’ buildings and refurbishments being undertaken with little attention given to future maintenance or replacement costs. This is not good value for the building owners.
Dr Hilary Davies is a senior lecturer in Facilities Management and Construction Management at Deakin University in the School of Architecture and Building. Deakin University will be offering a Masters in Facilities Management from 2011.
The above article was first published in the Dec 10-Jan 11 issue of Facility Management, in Dr Hilary Davies’ regular column Future FM.