CPD 08 2024: Polycarbonate facades for sustainability

Buildings consume far more energy than needed, and there is an increasing responsibility to design buildings that operate sustainably. Buildings account for approximately 41% of the world’s energy consumption, while lighting accounts for more than 20% of the world’s electricity consumption — more than the electricity generated by all nuclear power stations combined.

A study by Innovate UK of 49 “leading-edge, modern buildings” found that non-domestic buildings routinely use 3.6 times the amount of energy they are designed to consume and rarely live up to performance expectations.

Well-considered daylight designs and the optimised use of natural light reduce the need for artificial light, heat and cooling and are vital components for designers looking to reduce the building’s utility costs and carbon footprint. Studies also show that well daylit buildings improve productivity, focus and psychological wellbeing.

Learning objectives

• Understand the benefits of natural light to building costs and occupant wellbeing
• Explore polycarbonate as a potential solution to help maximise daylight
• Know the component features and sustainability of multiwall polycarbonate and plastics
• Aquire awareness of the considerations for polycarbonate facade design covering regulations, applications, installation and maintenance

Daylight makes a difference

We spend around 90% of our time indoors, which means the use of natural light in the form of a daylight strategy is a key component in modern building design, regardless of use or building type. Studies show that good access to natural light can improve productivity by 6% and creativity by 15%. This data is from the same 2015 Global Human Spaces report that showed two-thirds of UK-based office workers feel they do not have access to enough natural light.

Daylighting has been associated with improved mood, enhanced morale, less fatigue, and reduced eyestrain. Another benefit is faster recovery times in hospitals, with patients in rooms with access to natural light recovering on average 8% quicker than those in internal, artificially lit rooms

Maximising curtain walling and using more glass on the facade would increase daylight availability without reliance on artificial light. However, if not well considered, this approach can cause issues.

The sun is predictable but dynamic, moving from east to west. Depending on the time of day and year, the sun’s altering height results in glare and heat gain on different building elements. This means a shading device is required to protect the building’s occupants, be it brises-soleils externally, less effective manual shades internally, or automated shades that are effective but can be costly to maintain. If the glass is shaded, natural daylight is removed, lights are on, and the building’s energy consumption increases.

Choosing polycarbonate

Polycarbonates are a group of thermoplastic polymers containing carbonate groups in their chemical structures. The material is strong, and some grades are optically transparent, making them a potential solution to help maximise daylight in building design.

Features of polycarbonate facades include:

• Excellent strength/weight ratio – it is three times lighter than the average rainscreen.
• Very high impact resistance – up to 200 times that of glass.
• U-values as low as 0.49 are equivalent to centre-pane measurement. Some systems in vertical glazing offer a total U-value of 0.99. UV protective coatings are applied, controlling up to 99% of this harmful part of the solar spectrum.
• Design flexibility – it can be coloured, tinted and treated as glare or thermal control.
• The benefits of natural daylight are embraced with high light transmission, up to 52%.
• Installation of this type of system is quick, helping to de-risk the project and allow for faster air- and watertightness of the building envelope.
• A natural ability to be cold curved, allowing for a wider design aesthetic and functionality on site.
• Polycarbonates are easily moulded and thermoformed, making them applications such as glazing, cladding and rooflights. Any product considered should be independently tested to fire classification EN13501-1.

Sustainability

It has been widely perceived that plastic is not a sustainable material. However, new developments in polymer science are proving to be a gamechanger for sustainability in the manufacturing of polycarbonate facades.

Designers can considerably lower the facade’s embodied carbon by specifying a climate-neutral bio-based polycarbonate resin. The resin is produced using bio-circular feedstocks generated from used cooking oils and other bio sources which replace the normal fossil-based material.

Some manufacturers supply polycarbonate sheets manufactured from resin, with up to 89% of traditional fossil-based material replaced by sustainable bio-circular material. To achieve carbon savings, choosing a supplier that uses renewable energy for resin production is advisable.

Technological developments now allow facade glazing to be extruded with renewable energy generated on site. Brett Martin has a dedicated solar farm and wind turbine for this task. The net effect is a reduction in embodied carbon in the glazing panels by more than 80%.

This development has been made possible by the operation of a mass-balanced approach in the polymer industry, which is audited by the ISCC Plus certification system to confirm that the bio-circular material has been sourced sustainably and allocated via the company mass balancing system.

Regarding end-of-life options, it is important to check with your chosen supplier to ensure that the products specified are fully REACH and RoShcompliant and can be fully recycled.

Polycarbonate in use

Although using it as a glass replacement is the most useful application, with the highest payback in terms of utility cost reduction and occupant comfort, there are various applications for the specification of polycarbonate. The material can be used in the building envelope for glazing, cladding, wall lights, northlights and various other applications. The product’s versatility allows designers to create bespoke exteriors that meet their client’s goals. Below are specific examples of polycarbonate in use, which are also pictured.

Minimising compromises

An art studio in the Royal College of Art in London (pictured above) demonstrates the effective use of polycarbonate, minimising compromises at the facade. Glazing is at a low level, maintaining occupants’ connection with the environment, and the glare can be managed by lowering shades. However, instead of lights burning energy to compensate and maintain a working lux level, the polycarbonate above floods diffused light into the space without shade and artificial light. In addition, there is no compromise to design aesthetic, no excessive capital cost at build, no ongoing cost through use and no compromise on sustainable building materials.

Glazing

The ability to play indoor sports unhindered by glare is paramount to success. Use of polycarbonate facades in these kinds of spaces allows huge amounts of natural light to flood the playing surface without causing a glare issue. At Sports Ireland National Indoor Arena, in Dublin, no internal lights were required, creating a sustainable space that maximised the occupants’ playing ability.

Cladding Polycarbonate can also be used to finish more unusual industrial and commercial buildings due to its ability to follow curves and unusual shapes. The Centrocor Factory building, near Porto in Portugal, was clad with a clean, uncomplicated feel to mimic the needs of the internal environment.

Wall lights

The use of polycarbonate on the building envelope of Cardiff’s ice skating venue Vindico Arena is well showcased. The product’s versatility is evident, from colours to cladding, glazing panels and backlit wall lights. Differences in translucency, colour, and finish allow the same product to create vastly different aesthetics across the same space.

Northlights

A more traditional use of polycarbonate can be seen at the Seaflex warehouse on the Isle of Wight as a structured northlight in the roof rather than a sheet in an industrial built-up roof. Against glass, the weight savings make for a huge saving in the supporting structure yet flood a consistent light across the floorplate below with no glare and no high contrast between shade and light.

Beyond standardisation

The Floating Farm at Rotterdam, in the Netherlands, is a demonstration of an unusual design without compromise. For obvious reasons, weight is a key issue in this design, yet light entry to all areas is fully maintained through the use of polycarbonate in both the vertical plane and curved across the roof.

There are many other applications that showcase the versatility of polycarbonate, from multiple colours in one elevation and shaped finishes for aesthetics both externally and internally, to full corner tight radius curves that allow a seamless movement from one elevation to the next without the intrusion of steel.

Relevant regulations

Any manufacturer considered for a project should have independent, third-party fire testing completed to the EN 13501-1 standard. The importance of this cannot be overstated. Building facade material manufacturers, building designers, and the construction industry as a whole have an obligation to ensure the materials specified are safe to use for the intended application.

With regard to U-values, Part L of the Building Regulations was updated in 2023 and now requires that buildings conform to a minimum standard or maximum U-value of 2W/m2K. This means that for every degree difference between the inside and outside temperature, 2W of energy is transmitted through every square metre of that building element. The intention is to limit the use of mechanical cooling through the summer months. Some manufacturers of polycarbonate can reach figures as low as 0.99 – very thermally efficient.

There is inevitably a crossover between regulation, standards and design requirements. Other key considerations in facade design, to be explored further in the following section, include light transmission, sound insulation, water tightness, thermal bridging and connection to heat insulation.

Other design considerations

Light transmission

Interaction between polycarbonate and traditional glazing provides occupants with consistent internal light while maintaining a view to the exterior. Rather than negating the use of glass, in many cases, it can complement the polycarbonate glazing to offer best practice in daylight strategy across any building.

The same product can produce dramatically different results depending on the application. It is clear that polycarbonate vertical facade systems have a big impact on the interior of the building. However, a more effective approach would be to bring light in through the roof alongside vertical openings where the lightfall is clean, consistent and free of glare.

Another point of note is that high-contrast areas of light and shade can cause confusion and agitation. Polycarbonate systems in care homes, dementia care, and specialist schools can help where calm, consistent lightfall is incredibly beneficial to the building’s occupants.

Sound insulation

Carrying out the sound testing process is relatively straightforward. The test aims to ensure that the new development or conversion meets or exceeds the Building Regulation’s Part E standards and takes place before rather than after the development’s completion.

The testing process involves carrying out an airborne sound insulation test on party walls in adjoining properties. For flats, the process includes an airborne sound insulation test on party walls and an impact sound transmission test on floors. A report details the test results as well as any recommendations made, and it is used to certify building completion.

Watertightness

Watertightness testing is split into offsite and onsite testing. Offsite testing is performed at a testing centre during the facade design stage and is part of a bigger process to determine the facade’s performance and how it will react in use. Offsite performance mock-up testing is to understand the overall performance and functionality of the facade.

Onsite testing differs from offsite testing as it is used to check workmanship on a construction site. The main tests performed are hose tests and spray bar tests. Hose testing is used on closed-jointed systems, while spray-bar testing is used on open-jointed systems, windows, doors and cladding.

It is important to ensure that systems considered have well-designed drainage and watertightness to avoid condensation buildup. In some instances, extra steps can be taken in high-moisture areas to prevent this. This is similar for water transfer to the internal framework and space. Careful consideration is needed to ensure none of the above solutions affect the building’s finished aesthetic.

Thermal bridging

Thermal bridges are weak points (or areas) in the building envelope which allow heat to pass through more easily. Any interaction on the building envelope risks thermal bridging between the different elements. However, a thermally broken profile prevents this bridging effect.

Unlike some curtain wall glazing systems, the clips that connect the vertical panels to the purlins are independent, have no connection to the aluminium profile surround, and therefore do not offer the possibility of thermal bridging. This protects the U-value characteristics and allows the building to perform as built.

Light transmission causes glare, which is formed from the visible wavelength of the total solar wave. Solar heat gain is formed from solar energy passing through an object, such as glazing, in three ways: direct transmission, absorption and reradiation. This final area is created by the changing in wavelength from short to long that occurs after sunlight has passed through a clear material and is reflected off a surface. It alters the wavelength, which cannot pass back out of the space, and creates heat. In regard to U-values, the higher the rating, the worse the effect.

An additional element to consider is the infrared aspect of the solar wavelength. Unobstructed, you are seven times more susceptible to this infrared area than to air temperature, so people sitting at the perimeter of a building require additional air-conditioning, and those sitting deeper into the floorplate require the heating to be turned on.

All of these areas need careful consideration and depend on the use of space, people’s proximity to the facade, and the building’s performance needs. Polycarbonate has recognised values that not only can assist with all these components but also help drive down the cost of maintaining comfort, as it is an entirely passive response to a dynamic problem.

Lighting

Most common areas of internal workspace look for an internal lux level 300-500 lux, which is easily achievable through curtain walls in natural light but does not account for glare or heat gain issues. Polycarbonate allows light transmission to be maximised while avoiding heat and glare.

This type of system is not designed to replace traditional glazing in all areas but rather to complement glass and maximise the use of light, creating a comfortable working environment while passively reducing the building’s running costs.

Final thoughts

Budget is a key project factor, so it is noteworthy that glass is typically four times the cost of translucent polycarbonate glazing. Cold curving and the variety of shapes and colours it can achieve make it an attractive option for building designers.

A manufacturer offering bio-based materials and using renewable energy in its processes can largely overcome the materials’ environmental impact. This is coupled with the speed of installation for polycarbonate, which is up to 60% faster than glass.

The expected lifespan for polycarbonate systems is 20-25 years, with simple panel replacement available in accordance with a change of building use or client needs. Engaging with your chosen manufacturer early in the design process can help.

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