Pultruded GRP Windows and How They Reduce CO2 Emissions

Let’s start with a question on sport! What is the common denominator between squash, fishing, golf, skiing, tennis, motor racing and pole vaulting?

All of these robust activities rely on the best equipment to achieve maximum performance. That equipment relies on FRP’s to deliver those results.

You might know them better as ‘Carbon Fibre’, ‘Graphite’, ‘Fibreglass’, ‘GRP’ or just ‘Composite material’. However, it all means effectively the same. Fibre reinforced polymers (FRP’s) combine two very strong materials to form an astonishingly tough and durable compound that combines light weight with outstanding strength and performance.

Thermosetting resin is a tough and durable compound whose chemical curing process cannot be reversed by the subsequent application of heat. Therefore it cannot soften or melt under even extreme conditions, unlike thermoplastics (e.g. PVCU) whose thermal curing cycle will be reversed upon the application of heat, at any stage of its life. This makes thermosets inherently stable, dimensionally, in their own right – but with the binding and strengthening addition of glass or carbon fibres, the overall result is one of extraordinary durability and performance.

Whilst Sports Equipment Manufacturers, as well as the Motor and Aeronautical Industries have been quick to appreciate the advantages of this material, the UK Building Industry has not. In fact, to encourage its greater usage, the Building Research Establishment (BRE) at Watford, set up a specific department (NGCC – Network Group for Composites in Construction) in 2001, to promote the use of FRP’s for all kinds of external applications, whether structural or not. Since then there have been numerous projects undertaken which demonstrate the enormous possibilities and benefits.

Examples include:-

* The entire roof of the Millennium Dome (one million square feet, one kilometre circumference) is fibreglass. The World’s largest covered structure.
* The heat resistant nose cone on the NASA Space Shuttle is FRP.
* A footbridge over the Barcelona to Madrid high speed rail link has won a prestigious design award and is 100% GRP.
* The entire lorry cab, most motor cycle fairings and all TVR sports and Formula 1 cars – all have a complete ‘composite’ body shell for strength and light weight to give maximum performance – and no corrosion.
* Even the new Boeing 787 will use FRP nano-composites for 94% of fuselage and wings, according to Russell Maquire, Boeing’s Technical Vice President.

So, clearly this is a material with enormous potential, not to be under-rated! And, of course, not to be categorised as merely “plastic”, which is an incorrect broad brush generic. High technology plastic composites like this are at the cutting edge of modern materials – and significantly out-lasting and out-performing other traditional materials used today in many external building applications.

Manufacturing processes have also developed in tandem with the material development, to further exploit their advantages. Whilst flat pressing and moulded shapes had become common-place by the 70’s and 80’s, another challenge was being addressed, namely, the production of fibreglass in long continuous lineal lengths for various applications, including window profiles. This required multiple strands of glass fibre rovings and continuous matt to pass through a die together with the viscous thermosetting polyester resin. PVCU window profile is formed by pushing the liquid thermoplastic out through a die in a process known as ‘extrusion’. With fibreglass, however, the strands can only be pulled through from the other side, hence the process is known as ‘pultrusion’. The resultant end product has represented the latest in plastics technology for external building components, since the late 1990’s in USA and Canada – and since the early 2000’s in UK.

Pultrusion Technology Fenestration

For over 25 years, there has been little change in window frame materials with timber, PVCU and aluminium dominating all market sectors and fulfilling most applications, whether for housing or commercial projects, refurbishment or new build

However, Climate Change, environmental concerns and the consequences of Global Warming are causing a major re-think by leading specifiers, architects and designers. Initiatives by International Government’s to reduce fossil fuel burning and the generation of greenhouse gases, through improved thermal insulation, are also making the entire building industry re-evaluate the products being used today in order to improve thermal performance and longevity. Events as recently as the Montreal Conference in December 2005, to ratify the Kyoto Protocol, at which even the USA finally agreed to take the reduction of CO2 emissions as a serious necessity, emphasises that only by a common unified effort by everyone in their own personal sphere of influence can we collectively have any effect.

Each of the incumbent window frame materials used today, is a growing cause of major concern for specifiers, from an environmental viewpoint:-

* PVCU releases the ozone depleting greenhouse gas, chlorine, during manufacture and the end product is a poor thermal insulator due to the essential metal reinforcement inside, which acts as a cold thermal bridge.
* Aluminium has a high ’embodied energy’ from the original bauxite mining and then the enormous heat of the smelting process essential to its manufacture. The resultant end product is a very poor insulator since aluminium is, ironically, an excellent conductor.
* Hardwood used is invariably ‘Mahogany’ which only grows in the World’s dwindling Tropical rainforests (the lungs of the World) which already need protection from over zealous deforestation. Once again, the end product does not insulate too well and also creates the need for regular maintenance which itself has environmental consequences.
* Softwood does come from a sustainable source but the maintenance implications are appalling, both in terms of financial cost, as well as environmentally, from countless teams of maintenance engineers driving around to survey, paint and repair windows, in an attempt to stop them from biodegrading prematurely.

It was, of course, to put an end to this continual maintenance, in the mid 1980’s, that PVC windows were introduced in the first place! By comparison, pultruded fibreglass is nine times stronger than PVCU thus requiring no metal reinforcement, nor suffering the resultant cold bridging. It is stronger than steel and aluminium, weight for weight and bends less easily than either; it is non-toxic in manufacture and inert thereafter; requires zero maintenance – and insulates especially well, typically achieving ‘U’ values of 0.9 – 1.5 W/M2K. Life expectancy is 50 – 75 years. Co-efficient of expansion is negligible, being similar to glass itself. It is indestructible by natural forces and cannot biodegrade. Upon disposal it can be ground down and used as a filler in concrete, since the glass fibres improve the binding capability of the mix.

Cost: New technology products invariably cost more in order to help recoup some of the extensive R&D initial development costs that created them. However, it is reasonable to expect that there should also be some practical advantages to offset this higher cost. Fibreglass is no exception:-

* A formal Whole Life Cost study undertaken by BRE has shown that the longer life expectancy of Pultruded Fibreglass, over PVCU, makes it better ‘value’ over the 30 year period of the study, even though the initial capital cost is higher. Additionally, fibreglass has a further 20 – 45 years of life remaining, whilst the PVC has already had to be replaced – and may well have to be again during the life of the fibreglass alternative.
* Despite the performance, environmental and thermal advantages of Fibreglass over aluminium, it invariably offers an actual reduction in cost over most like for like aluminium window designs, despite the significantly lower insulation U values and longer life.

This concept is no longer embryonic but is commencing in full production on both sides of the Atlantic. For example, in USA, fibreglass has become the ‘window of choice’ for the high end residential market and the fastest growing material in the Commercial sector. Reflecting this, the two leading timber window manufacturers have both invested heavily in this ‘new’ technology and built huge 200,000 sq feet production plants dedicated solely to pultruded fibreglass windows. Clearly, this product is here to stay!