CPD articles

CPD: Translucent Polycarbonate Panels

3 March 2014

Tougher than glass, lighter than steel, translucent polycarbonate panels should be on every facade specifier's list, says Graham Kent-Jackson.

Translucent polycarbonate panels were pioneered as far back as 1971 and eye-catching examples of their use can be found on a range of building projects throughout the world. The toughness of the material, durability and lightness are some of the main advantages.

The panels are primarily used as an alternative to glass or GRP (glass reinforced plastic) for facade applications for new-build and refurbishment projects in the commercial, industrial, retail, education, healthcare and sports and leisure sectors.

The panels can be used to provide large-scale rainscreens or curtain walling that bring a monolithic element to the building envelope, to glazing elements such as light bands or window strips. They can also be used for roofing, canopies, rooflights and interior design elements. By backlighting with LED or ambient lighting systems polycarbonate panels can also bring a wow factor to a building.

Polycarbonate panels are also popular because they perform well on a variety of fronts. Thermally, they can they can be manufactured with U-values as low as 0.71-0.77 W/m²K as a single-wall construction and 0.36-0.43 W/m²K as a double-wall construction. As such, they can be used to allow natural daylight (with light transmission of up to 66%) into a building without compromising its thermal integrity. Panels with U-values as low as 0.36 W/m²K, compared to double glazing at 2.8 W/m²K and single glazing at 5.8 W/m²K, are capable of reducing energy losses by up to 80%.

They also perform to a high level acoustically, despite their light weight, with a sound insulation value of up to 27dB – meeting DIN EN ISO 1640-3 in test facility conditions. A value of up to 43dB is achievable with a double-wall construction. That said, they do not have the same sound reduction qualities as glass so consideration needs to be given if they are being considered for a sound sensitive area.

In addition, polycarbonate panels are:

Polycarbonate panels can be used in a wide range of applications

Though the material is highly flexible in use, it can be more expensive than glass and other plastic. Also, polycarbonate panels are not very resistant to scratching, marring and abrasive surfaces. As a result, denting is possible on the surface if care is not taken.

Polycarbonate panels are sensitive to abrasive cleaners, alkaline cleaning products and solvents. But the product can be cleaned with soapy water so there is no need for an abrasive material – which can also scratch glass. We would always advise clients wanting to, for instance, bond vinyl graphics to the surface of the material to use the right polycarbonate-compatible adhesive.

Standards

In addition to helping project teams meet key acoustic and thermal regulations and air and water permeability performance, polycarbonate panels have been tested and certified with regard to fire resistance. Depending on the thickness of the element and the composition of the material, typical products can meet DIN4102 B1 (low inflammability) or B2 (normal inflammability). Panels achieve class 1Y of BS 476 Part 7: Surface Spread of Flame, and polycarbonate ceilings meet class B-s1, d0 (the highest rating) of EN 13501.

They are tested to European standards for fire and have achieved Class B for ACR fragility tests.

Aesthetics

Translucent polycarbonate panels are available in a wide range of standard and bespoke colours and degrees of transparency. Blocks of coloured panels can be designed into patterns and illuminated facades created by combining them with LED or ambient lighting systems to give the ultimate design aesthetic. As a thermoplastic, polycarbonate can also be curved to create completely bespoke elevations.

They can also be specified where the interior panel is coloured differently than the exterior panel to give a 3D effect, where the actual panel is coloured differently through its own thickness, with a metallic-look pigmentation, or with a fluorescent surface that glows at night. All can be backlit for additional effect.

Roofing

All the qualities that made translucent polycarbonate panels eminently suitable for facade applications, also make them ideal for roofing ones.

These range from curved and flat rooflights and canopies, through north lights and gable roofs, to rooflights for corrugated sheet applications – all elements that introduce natural daylight, and the energy savings associated with that, into large or small interior or exterior covered spaces.

Translucent tiles suitable for roof pitches as low as 15˚ are available in a range of colours for all panel thicknesses between 30mm and 50mm and in flexible widths with closed edges. These give excellent U-values as well as the option for a special finish to minimise solar gain.

Canopies

Translucent flat and curved canopies are available for pitches and radiuses as low as 5˚ and 3m respectively using an aluminium glazing bar system that makes them especially suitable for high free spans and the bypassing of such. Customised sizes make them especially easy to incorporate into existing roof constructions with profiled sheeting or composite panels where maximum natural light is needed.

Rooflights

Like canopies, translucent flat and curved rooflights are available for pitches and radiuses as low as 5˚ and 3m respectively and in customised lengths and widths with closed edges, all of which are easily and quickly installed using prefabricated interlocking modules. Rooflight systems can be accessorised with flaps to aid natural smoke and heat ventilation while the absence of glazing bars and minimal use of alloy composites creates an almost seamless interior finish.

Manufacture

Polycarbonate is a thermoplastic – a polymer that becomes pliable or mouldable above a specific temperature and returns to a solid state upon cooling. It has a glass transition temperature of about 150 degrees C so it softens gradually above this point (the recommended processing temperature is around 280-300 degrees C).

It is a member of the group of “engineering thermoplastics” which are grouped together not because they are similar in chemical structure or morphology but more due to specific properties that allow them to be used in rigorous applications, particularly in the construction, electronics, automotive and manufacturing sectors. Polycarbonate is used in motorcycle helmets, for example, while acrylonitrile butadiene styrene is used to manufacture car bumpers and dashboard trim, and polyamides (nylons) are used for skis and ski boots.

Translucent polycarbonate panels are manufactured in a very similar way to many thermoplastic products.

To begin with, polycarbonate granules are fed into an extruder which heats them to flow temperature. The molten is then extruded through a die head in the shape of the panel. Colour and UV stabilisers are added via secondary or co-extrusions.

Then, as the panel moves along the automated line, a protective film is applied and the panel is trimmed to length. Polycarbonate does not require specialist tools for cutting, a fine-toothed circular saw is usually sufficient.

Extruding a panel uniformly, however, requires many variables which require strict control, primarily the cooling of the material and the speed of the process. If these variables are not controlled sufficiently, the panel’s shape and structure will be affected and irregular.

Polycarbonate is fully recyclable, with up to 30% of reworked or recycled material used in each panel produced. Polycarbonate scraps from industries such as luggage fabrication, car production, electronics and household appliances,
and digital storage media such as CDs and DVDs, are all a tradable commodity.

Installation

The tongue and groove coupling of a polycarbonate panel is an exemplar of modern and lean construction, with large-scale building widths of up to 500mm enabling facades of more than 200m long to be erected and panel heights of up to 25m to be mounted in one piece.

A typical polycarbonate wall system uses an air- and water-tight framing system comprising aluminium perimeter channels with head, base, side and corner sections, and front and rear thermoplastic elastomer gaskets.

Supplied anodised, mill-finished or polyester powder-coated to any RAL colour, this framing is fixed to the structure. The translucent panels are delivered, depending on the finish, with protective foil on one or both sides and this should be retained throughout the installation process.

The panel ends are sealed with a combination of aluminium/butyl tape and vent tape to prevent water, insects, gases and other fine particles from entering. All sealants and tapes have to be polycarbonate-compatible, and all silicone has to be neutral and solvent-free.

The first panel is inserted into the perimeter frame and held in place by an aluminium fastener that slots into the panel’s tongue and groove joint. Clips, continuous fasteners or translucent mullions may be used depending on wind loads, fixing centres and aesthetic requirements.

Once the fastener is fixed to a horizontal rail the next panel is inserted and pushed into the first panel which covers the aluminium fastener from external view. This process continues along the wall structure.

A key aspect of this method is that the panels are “retained” rather than fixed, allowing them to glide along the fasteners when thermal expansion and contraction takes place. The expansion coefficient for polycarbonate is 0.065mm per degree C per metre – three times the expansion coefficient of aluminium. As a rule of thumb, it expands 3mm per metre per 50 degrees C difference in temperature. cm

Graham Kent-Jackson is managing director of Rodeca


Panels get a piste of the action

Rodeca’s Deco-Colour polycarbonate panels were specified for the Chill Factor E centre in Manchester

FaulknerBrowns Architects was adamant it wanted to use Rodeca’s translucent cladding panels on the UK’s largest indoor ski/snowboard centre, Chill Factor E at Manchester’s Trafford Park.

Some 4,000 sq m of Rodeca’s Deco-Color polycarbonate panels were specified as a rainscreen system to the lower halves of the sides of the two main elements of the £31m centre – in sky blue for the main slope (at 180m, the longest in the UK) and raspberry red for the smaller training slope.

The 250,000 sq ft of internal floor area at Chill Factor E is divided into two distinctive zones: a warm Alpine streetscape containing bars, restaurants, shops and an ice climbing wall; and the snow slopes which are themselves divided into three pistes to cater for skiers and boarders of all abilities.

When it came to the specification of external envelope materials the Rodeca panels were up against metal cladding systems and GRP, but project architect/partner Ben Sykes said: “We resisted a lot of pressure to replace the cladding feature with a lower spec option.

“The Rodeca material is backlit by night and reveals the structural depth of the construction. It also has the ability to ‘lift’ the appearance of the more basic cladding components.”

Rodeca’s 500mm-wide panels are manufactured with a tongue and groove coupling and are typically fixed with aluminium fasteners.

At Chill Factor E, the exterior Deco-Colour panels were “lined” with Rodeca’s 40mm-thick Kristall panels by specialist contractor Lakesmere for main contractor Sir Robert McAlpine and client Extreme Cool. Lakesmere laid them vertically onto mill finished continuous aluminium fasteners spanning cladding rails at typically 1,800mm centres.

Graham Perrins of Lakesmere said: “The areas of Rodeca cladding to the bottom of the ski slopes where they were cantilevering were subject to severe wind loads from front and back so we were tasked with providing structure to these zones, capable of withstanding the imposed loads.

“The system is usually provided with individual aluminium clip fasteners, but a continuous fastener was specified due to the nature/height of this project and the wind loads subjected.”

The Studio at Magdalen College School

Oxford school sports a new facade

Translucent cladding panels from Rodeca feature on a new extension to an independent school in Oxford. Some 1,402m of Rodeca’s Kristall panels were specified by architect Original Field of Architecture for the first floor element of a new sports building that also incorporates three new classrooms and a new office for the geography department at Magdalen College School.

The sports department now features a new entrance to the sports hall, new offices, a team debrief and seminar area, and a sports analysis suite. But the most exciting addition has been the multi-function room – The Studio – which provides seating for up to 200 and with its sprung floor can be used for a wide range of activities from dance to table tennis and fencing. Here, the Rodeca panels are interspersed with feature windows of coloured and bi-coloured glass.

It is this element that features the 50mm thick Rodeca panels as cladding which was installed by Roclad Systems for main contractor Benfield & Loxley onto an anodised aluminium frame with 60mm clip fasteners.

The Kristall panels comprise 10 layers of polycarbonate capable of delivering U-values as low as 0.80 W/m2K, and in the case of Magdalen College School, were supplied with a 20-year UV guarantee.

Original Field of Architecture had not used Rodeca panels before and was impressed with their use on the Trinity Laban Conservatoire of Music and Dance in Greenwich, London.

Click here to be taken to the online CPD test paper for March 2014

Comments

Never use polycarbonate anywhere near a persons reach...so soft.

Guy Jackson, 6 March 2014

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