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Theme: cladding

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The potential for a new, revolutionary relationship between architects and material scientists is set to inspire a 21st-century renaissance of the built environment, promoting an alliance of digital design and emergent materials, and finally giving cladding the attention it deserves.

The built environment of the 21st century will be transformed by nanotechnology and mass customisation. Standardisation, so beloved by policy makers in the UK, which resulted from a misunderstanding of the potential of the industrial revolution and arguably was never applied successfully to architecture, is obsolete. This is now the post-Ford, post-Egan era, with the potential for a new relationship between architects and material scientists that will reinvigorate the role of architects within construction. The alliance of digital design technology and emergent materials has the potential to create a revolutionary dynamism within architecture.

Architects James Timberlake and Stephen Kieran of Kieran Timberlake Associates, Philadelphia, who are known for their sophisticated designs for 'Ivy League' universities, have been researching this proposition for the past four year, having received the first Benjamin Henry Latrobe Fellowship from the American Institute of Architects. But how do you demonstrate the potential of nanotechnology and mass customisation?

Kieran Timberlake's answer is the SmartWrap Pavilion, which was on display at Cooper Hewitt National Design Museum, New York, from 5 August-10 October 2003.

The SmartWrap concept will deliver shelter, climate control, lighting, information display and power with a printed and layered polymer composite. The aluminiumframed pavilion is clad in a printed skin based on a combination of polyester and its derivative polyethylenetelepthalate (PET), which was developed with DuPont. Fully developed SmartWrap will incorporate phase-change materials to mimic thermal mass and act as thermal regulators. Phasechange materials can store five to 14 times more heat per volume than naturally occurring latent heat stores such as water, masonry or rock. Lighting and information displays are delivered by organic light-emitting diodes (OLED), which are thin, flexible and self-emissive. The OLEDs were developed with DuPont Displays. Shelter is provided by the PET film, which is colourless and transparent. Entrapped pockets of aerogel, supplied by Aspen Aerogels, provide thermal resistance. This layered assembly achieves the thermal resistance of an insulated 400mm concrete-block cavity wall at approximately one-hundredth of the weight.

Noting the major power blackout experienced this summer in North America, including New York, it is reassuring to note that SmartWrap also incorporates organic photovoltaic cells to generate electricity. The curator of the exhibition, Matilda McQuaid, stated that the pavilion 'is intended as a kind of provocation to designers and architects'.

She also noted that SmartWrap should be available commercially within five to ten years. The main pavilion is printed with a mass customisable pattern, which represents the proposed layered assembly. A 2.4m square panel next to the pavilion demonstrates the working components of SmartWrap. Although this is currently a future product, it demonstrates a highly integrated use of nanotechnology, which can be tailored to suit specific site conditions and a wide range of building typologies.

Polymer composites The layered and composite quality of fibrereinforced polymers (FRP) facilitates the introduction of resins, fibres and layers with specific additional attributes, including thermo-chromic pigments and electro-luminescence. Polymer composites can facilitate the delivery of nanotechnology, creating building components that incorporate as-yet-unseen functionality. Brookes Stacey Randall researched two complementary techniques for a new set of exhibition spaces for Woking Galleries. The client's vision for the town's new cultural centre set out a diverse agenda to serve the widest possible constituency of local people. Brookes Stacey Randall's design comprises a set of articulated 'pavilions', which express the diverse functions of the brief, yet, read as a totality, to represent Woking Galleries as a legible and inclusive institute.

The 'beam' houses the history and exhibition galleries, and administrative accommodation.

In a gallery for the display of art, receiving international touring exhibitions, the internal temperature needs to be controlled closely, and the light levels adjusted gradually from entry to the viewing of the painting or drawing. Thus a high proportion of the gallery wall is opaque. We thought it was essential to animate this building externally, to transform the 'black box'. The cantilevered galleries are clad with an iridescent and environmentally responsive FRP rainscreen skin, creating a dramatic and memorable profile, which would always be different at each time of day or each visit.

The gel coat of the polymer-composite rainscreen panels incorporates thermochromic pigments. The panels, when warmed by the sun, gradually change colour. Three colour 'states' were incorporated in the pigmented layer of each panel. Even on an overcast English day, changes in environmental temperature would cause the panels to change colour depending on their location within the facade. The intention is that the gallery should shimmer whilst providing ideal conditions for the display of art internally.

Brookes Stacey Randall also researched the use of electro-luminescent panels, forming the soffit of the 'beam'. Lighting and circuitry were integrated directly into the polymer-composite panels. An extremely thin phosphorescent sheet with all the circuitry screen-printed onto woven glass cloth enables the panels to act as glowing planes of light. Electro-luminescence and thermochromic pigments are only two initial examples of the diverse 'intelligence' it is possible to embed into polymer composites.

UV stability UV stability is a vital performance criterion critical for all external applications of polymer composites. Early polymers suffered from yellowing, chalking and fading of strong colours such as blues and reds. The weathering of a polymer composite is a result of the combination of UV radiation, moisture and heat. To ensure long-term durability it is critical to avoid embrittlement of the polymer and loss of structural capacity.

I am concerned that too many architects are influenced by highly publicised past failures, whereas today there are two distinct advantages when considering the selection of polymer composites. Firstly, we have the experience gained from projects such as Mondial House, built in 1975, which demonstrates that the polymer-composite cladding has proved durable for over 25 years. When it was re-inspected in 1997 no signs of structural damage were found and only minor surface degradation was identified 1. Part of the success of Mondial House is based on the use of a fire-resistant GRP with a 'marine-grade gel coat'. The complete system complies with BS476 Part & Class 1 and Class O requirements of the UK Building Regulations.

Secondly, since 1975 companies such as Scott Bader, which supplied the resins for Mondial House, have continued to develop and test resin systems for external use. This has included long-term testing in sites of high insolation, high moisture and temperature extremes such as Florida, and accelerated UV stability testing using the EMMAQA test method. This test uses mirrors to intensify sunlight, testing for yellowing and loss of gloss. Progress on durability has been evolutionary and not a new revolution in the chemistry of polymer composites. However, the durability timescale has effectively doubled in the past 25 years, with improvements in gloss retention and colour stability.

The Network Group for Composites in Construction (NGCC) was founded in 2000 to foster communication and partnering with the aim of encouraging the use of composites in construction. For more information see www. ngcc. org. uk.

Arup gets blisters Shepherd Robson has specified polymer composites for the re-cladding of Arup's headquarters building at Fitzroy Square. The meeting room 'blisters' are doubly curved polymer composite cladding supplied and erected by GIG Fassadenbau. The cladding was manufactured in Germany and post finished, following extensive hand sanding, with a dark green spray-applied PVDF. The colour of the cladding is inspired by German cars, to match directly Audi Green and Polo 'Mint Green'. The physical realisation of architectural ideas is dependent on the bringing together of concepts, processes and materials. Polymer composites offer a provocative route for delivering design intent. This group of materials and manufacturing processes excels at all scales of production - from the bespoke or one-off and serial or batch production to mass production.

Offering an almost infinite matrix of possibilities, polymer composites are truly a designer material for the 21st Century, capable of realising almost any form architects can conceive and digital design tools describe. The interest and exploration of curvilinear form is driving renewed interest in polymer composites, a market-led demand to which further major curtain walling suppliers will probably respond.

In case of fire Understandably, fire is one of the most emotive subjects in the built environment. The selection of appropriate construction is too often dogged by myths and misinformation.

The Building Regulations focus on the lifecritical aspects but the past 10 years have also seen an increasing emphasis placed on the need to minimise the economic risk of loss of property, driven primarily by insurance companies and research organisations. This has had a significant effect on the use of composite metal panels (or sandwich panels). The Association of British Insurers (ABI) has produced a useful Technical Briefing: Fire Performance of Sandwich Panel Systems, May 2003. This focuses on the use of composite panels in factories, particularly food factories. Written by the Building Research Establishment (BRE), it is primarily intended to be read by commercial property insurers, although the briefing notes that 'the findings will also be of interest to construction professionals'. This is a useful introduction to fire-rated composite construction and the role of the Loss Prevention Certification Board, which is owned by BRE.

The development of fire-rated composite panels has been driven by well-documented fires and the need for fire-rated cladding within one metre of a property boundary.

An apparent dichotomy has developed between fire engineering and prescription.

Fire engineering is now well recognised as a strategic design activity that can help deliver the original spatial intent, potentially reducing the overall cost of building, whilst maintaining fire safety. It is still possible, however, to encounter 'knee jerk' reactions to fire risks. For example, I recently received the Employer Requirements for the design and construction of a major new factory, which simply stated 'no foam shall be used in the cladding'. This misunderstands the materials science of a range of foamed materials used to form composite panels, with well-tested fire performance. The ABI report also notes that one of the major causes of fires was poor management of fire risk: 'Experience from fires in food factories has indicated that fires start often because of poor standards of fire safety management'. The core material that has caused the greatest concern is expanded polystyrene (EPS), especially when used to form insulating internal partitions in applications such as cold stores and clean rooms.

Composite construction can be defined as the bringing together of materials with very different physical properties to form a single component. Combining these materials creates an element of significantly higher performance. The incorporation of fire resistance by the choice of core material and facing skins, whilst maintaining strength and thermal performance, is an excellent example of the application of material science to create affordable high-performance cladding components.

If you are considering specifying firerated composite cladding, there is now a wide range of core types:

l mineral wool lamella;

l Foamglas;

l polyisocyanurate (PIR);

l dual core of PIR and mineral wool;

l phenolic/expanded polystyrene hybrid.

It is important to establish which systems have been tested and have received LPCB or Factory Mutual Research Corporation approval. Many manufacturers sell nonaccredited ranges alongside their tested products. It is also essential that the product is unchanged from the one tested, so it is essential to check this prior to specification.

Fire-rated composite panels with steel skins laminated to a mineral-wool lamella core are produced by a range of manufacturers including Corus Panels & Profiles, Paroc and Panel Systems. Paroc panels are manufactured in Finland and the United Kingdom. This year, Euroclad has opened a £4 million manufacturing facility in Cardiff, which is a fully automated line for the production of laminated mineral wool lamella-cored fire-rated panels. The laminating line can produce panels up to 12m in length and 200mm thick. An 86mm-thick Euroclad FireMaster panel, when steel-faced, offers the following fire performance: 60 minutes integrity and 60 minutes insulation when tested to BS 476 Part 22. Hunter Douglas has established that it is possible to achieve 60 minutes fire resistance with a composite panel that has an aluminium skins and a mineral-wool core. Its Luxalon Pyropanel achieved this when it was tested to BS 476 Part 22 at Warrington Fire Research.

The primary advantage of using mineralwool lamella as core material is its non-combustibility. However, it does also provide acoustic separation. For example, an 86mmthick Euroclad FireMaster panel provides a 30dB reduction in frequencies between 100 and 5000 Hz. The disadvantages of mineral wool are that it provides approximately 50 per cent less thermal resistance when compared to polyisocyanurate (PIR) and it is a relatively dense material. Thus mineralwool-based panels are thicker and significantly heavier than foam-cored panels.

Broadly speaking, to achieve the same thermal performance (U-value), a mineral-wool lamella-based panel is twice as thick and twice as heavy when compared to a PIR-based panel. Metecno's response to this dilemma is the FireMet panel, manufactured with a dual core, which is 25 per cent mineral wool and 75 per cent PIR. An 80mm-thick FireMet panel achieves a U-value of 0.25W/m 2K and a fire resistance equating to LPS1181 Grade A with only a 27 per cent increase in weight compared to a PIR-based panel.

Panel Systems markets a system that is based on a Foamglas core. This was developed jointly with Pittsburgh Corning, the producer of Foamglas. Kingspan has manufactured continuous foamed in-situ panels using polyisocyanurate (PIR) since 1986, achieving LPC approval for its KS 1000RW panel system in December 1996. This now forms part of its Firesafe range.

EDM Spanwall set itself the challenge of developing a core material that would not add to the fire load of a building, and that would pass the FM 4880 and LPC1181 tests.

It also set the goal of out-performing the thermal and structural characteristics of polystyrene. The core material, named Spancore, is a matrix of Expanded Polystyrene (EPS), phenolic resin and 'other fire retardant materials' 2. Although denser than EPS, the core is significantly lighter than mineral wool, and it also offers good thermal and strength characteristics.

Exploiting the rainscreen The emphasis on non-combustible facades has also resulted in increased usage of rainscreen cladding with fire-rated internal walls.

Ame reports that 80 per cent of its production in 2002-03 was rainscreen cladding. One advantage of rainscreen cladding over an insulated composite system is the minimisation of thermal bowing, as a rainscreen panel has a much smaller thermal gradient through the panel. Ame has developed with VM a zincfaced composite rainscreen panel system - the rear of the zinc coil is precoated with an 'intermediate' layer that enables it to be bonded successfully to an aluminium honeycomb core.

The balancing internal sheet is typically of coated steel. These zinc-faced Proteus hr panels have been used to clad the new Ebor Stand at York Racecourse. The drawing on page 28 shows the build up of Ame's Proteus hr panel system, illustrating the aluminium honeycomb core and aluminium carrier system.

Corus Panels and Profiles has developed bi-metallic sheets, which can be used for standing-seam zinc roofing and cladding.

Rainscreen panels can also be produced, but the maximum width is limited currently by the 670mm coil width. Using the patented Pegal process, Corus apply 8 microns of zinc to an aluminium substrate, which is 0.7 or 1mm thick. Sold under the trade name Falzinc, this product has a number of advantages when compared to through-thickness zinc sheet. It is about three times lighter, it can be formed on site to below -35°C (any cold weather that is tolerable to site workers is a more reasonable parameter than this material science 'fact') and, importantly, it avoids sweat corrosion without the need for separating layers. Corus can also use the Pegal process to coat aluminium with titanium, so Gehryesque dreams should now be more affordable and flatter!

Working with wood The past five years have seen a renaissance in the use of timber cladding, with many of the applications going well beyond conventional weatherboarding. The TRADA guide to External Timber Cladding (2000), written by PJ Hislop, is a useful starting point for anyone considering specifying timber cladding. For example, it warns that European oak will exude tannin as it dries, and this will appear as black deposits on the face of the oak cladding. Rainwater will wash the tannin down the face of the cladding and can stain surfaces below, particularly masonry or concrete. The corrosive potential of the tannin means that it is wise to use corrosion-resistant fixings.

Brookes Stacey Randall Consultants advised Bennetts Associates on the timber cladding of Hampstead Theatre (AJ 6.3.03).

This is a highly integrated assembly faced with a warm-coloured hardwood, called jatoba. Ecotimber of Cardiff supplied the timber with Forest Stewardship Council (FSC) certification as evidence that it came from a sustainable source. Bennetts sought a horizontal expression of timber slats for both the rainscreen cladding and the window louvres. The shading devices were both fixed and moveable, requiring very careful integration with the Reynaers Aluminium curtain walling. The rainscreen was panellised and fixed back, using proprietary aluminium fix cleats and rails that made full allowance for thermal and moisture movements. In essence an apparently complex facade was made as simple and buildable as possible, whilst fully respecting the original visual design intentions, by a careful collaboration with Bennetts and all the suppliers.

I am concerned that in recent times cladding has not received an appropriate level of attention from the architectural profession.

Many of Palladio's projects in Vicenza and Gaudi's in Barcelona are 'only' overcladding.

At Enschede Textile Centrum, (AJ 12.2.02), Brookes Stacey Randall, with IAA, revitalised a failing textile school. The western red cedar cladding had a vital role to play - the laboratory block is clad in reconstituted black granite, which is typically used for paving. The former factory is shaded by cedar and on the right the bike store and electricity substation are clad in simple slats of cedar. Even the humblest of building types can be transformed by carefully considered cladding.

Michael Stacey is the author of Component Design, a founding partner of Brookes Stacey Randall Architects, academic leader at London Metropolitan University Department of Architecture & Spatial Design, and research professor at University of Waterloo, Ontario

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