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The market place for the production of window frames is vast. There are some fifty different timber and PVCu profiles manufactured in the UK alone. In 2009 The Glass and Glazing Federation (GGF) commissioned Palmer Market Research to undertake a survey to assess the annual window market value. To the year end, a total of £3.96 Billion was spent on private use and £1.4 Billion on commercial use giving a total worth of almost £5.4 billion per annum. If broken down to the types of materials used, this equates to 54% Poly Vinyl Chloride unplasticised (PVCu), 26% Aluminium and the remaining 20% of the window market begin timber.
The choice of materials for window profiles is now quite wide. Traditionally all windows were made from timber, the only sustainable material available. Using good quality timbers, traditional paints based on linseed oil and lead oxides, sealants such as lined oil putties and mastics, these windows lasted well. The advent of alternative materials during the twentieth century, initially steel and more recently polyvinyl chloride (PVC) has changed the nature of the window industry and not always for the best with regards to sustainability.
Timber window replacement contract- Sanctuary Housing Association
Crawford Place, W1
When selecting construction materials it would be ideal if we had products to chose from that were benign from both a planetary and human standpoint. However, in our complex industrialised society, our choices are rarely simple, so we must usually make compromises.
In one corner stands the PVC industry, represented by institutions such as the European Council for Vinyl Manufacturers (ECVM) and the British Plastics Federation (BPF), defending PVCu as a popular material, which is also friendly to the environment and according to their scientists the most benign material to use for window profiles is PVCu.
The BPF states the issue surrounding the energy used in PVCu production is very easily dismissed when you look at the science of the production process. It only requires 0.49 tonnes of crude oil constituents to make 1 tonne of PVCu. Following on from this, it must also be noted that because PVCu is such a light material, less energy is used to transport it once produced.
The plastic window manufacturers also claim their windows have energy advantages over some of their alternatives because they are so durable and require only minimal maintenance. Timber windows require regular painting, whereas PVCu windows require only the occasional wash. As well as energy savings, this also gives PVCu windows a distinct advantage over the "lifetime costs" of the window
However, on the other side of the fence environmental campaigners, such as Greenpeace and Friends of the Earth (FoE) are denouncing PVCu as environmentally damaging.
The UK Fire Brigades Union has expressed its concerns about the use of PVCu in building materials. Arnold Tarling, a surveyor with 22 years fire risk experience said that PVC windows failed long before timber windows, the frames expand (in fire) and when that happens internal linings bow allowing fire and smoke to get between them and the frame. With timber frames that doesn't happen. Further research was undertaken by the BRE. They found that "wooden window frames offer nine more minutes fire resistance to that of their plastic counterparts".
Environmental campaigners are now promoting the merits of timber. Greenpeace suggests that traditional materials, such as sustainably harvested wood are the best substitutes for PVCu products. Unlike just a decade ago, when logging of ancient or old growth forests lead to a decrease in biodiversity and as habitats were destroyed, the FoE looked at the association of timber with climate change.
The main problems with timber are commonly conceived to be "durability" and "maintenance cycles", but as a material for frame manufacture, timber offers a number of significant environmental and performance advantages. Timber is a renewable resource, particularly if originating from a well managed forest, unlike that of its counterpart which requires oil constituents for production. With appropriate design, installation, maintenance and suitable timber preservation system, timber windows are exceptionally durable.
The total production cycle for timber windows uses far less energy than that used in production of PVCu. Modern timber frames can offer the best thermal characteristics of any frame material currently available. Responsible forestry makes no overall contribution to climate change and may cause a net decrease.
Although, potentially, timber is an environmentally sensitive choice for construction of many building components, the environmental impact does depend on the sourcing of the timber. The world's rainforests are being decimated and the primary driving force for this is timber production. All independent studies show that claims of "sustainable" production are deceptive. The honourable exception is independently certified timber.
Many timbers and timber products are claimed to be the result of sustainable production and there are a number of certification schemes in existence, which purport to show this.
In the opinion of many leaders in the field of environmentally sensitive building, only independent certification means much. The Forestry Stewardship Council (FSC) is the only body providing independent certification of timber products as being sustainably sourced.
The FSC is growing rapidly and certified timbers are slowly becoming more widely available, although to date, some of the very large DIY outlets have tended to monopolise the supply chain making it relatively difficult for smaller producers to obtain reliable supplies at sensible prices. It is extremely important to be aware, when buying for example joinery products, that the producer of the product must themselves be FSC certified, it is not enough for a manufacturer to say they are using FSC timber. They must be certified themselves to provide a fully validated chain custody.
FIG: Certified timber logo, products only contain material from FSC certified forest that meets environmental and social standards of FSC
Source: FSC website - www.fsc.org.uk
If independently certified timber is not available, then the sensible choice is to avoid the problematic area, which include the tropical rainforests and areas where clear felling of old growth forest is being undertaken on a large scale. The latter includes timber imported from parts of Russia (for example Siberian Larch species) and certain other areas
Clients should however be aware there are many environmental considerations to take into account when assessing the "green" credentials of a product, such as ozone depletion and pollution to our air and water supply. For example, a product may have high-energy requirements for processing that will produce CO² and contribute to climate change, or it may lead to environmental problems through its maintenance or disposal.
Polyvinyl Chloride is marketed as popular, safe to use and widely used in a diverse range of products in the construction industry, including doors and window frames. The issues of concern, with regards to PVC, relate to the manufacture, use and disposal of the material and the additives that are combined with it to make PVC products. The points of concern include the production of poisonous by products during accidental burning at the end of the life stage and the use of additives such as plasticizers. These concerns are of the upmost importance.
In 2008 the Department for Environment, Food and Rural Affairs (DEFRA) undertook a study using a wide range of applications used during the production cycle of PVC. Analysis of the Summary of key inventory flows for window profiles shows that PVCu profile systems consume marginally more total primary energy than the timber profile.
PVCu Installation-Midwinter Court,
Shepherds Bush Housing Association
Like many manufacturing process, the production of PVCu involves the use of raw materials that can be hazardous if improperly handled. In day-to-day operations the PVC industry has a good record of safe operation.
The fossil CO² emission profiles, which are dominated by gas consumption, are similar for both products. The timber profile system benefits from biomass CO² uptake, due to tree growth and emission of CO² at the end-of-life during degradation. As a result, the overall CO² balance for the PVCu profile system is 15% greater than that of timber.
Over the life cycle of the products, the timber profile system generates 43% less waste than the PVCu profile system, due to lower waste generation rates in both the production and end-of-life phases. For the PVCu profile system, the higher waste generation in the production phase is due to waste arising from the production of raw materials. The greater waste generation at the end-of-life is due to the lack of degradation of PVC in the landfill. However more recent developments in recycling PVC may have an overall effect on this figure in time.
The PVC profile has greater air acidification impact than that of the timber profile system that is a result of SOx emissions attributable to PVCu manufacture, during the production phase.
Overall, the sentiments of the summary are that PVCu is not the most environmentally benign material to use for window profiles and does have effects on the environment, mainly due to the complexities of production, but that these impacts are not considered excessive, in relation to an alternative such as timber, which has environmental effects itself.
PVCu frames are popularly promoted as "maintenance free", but in fact do require regular cleaning to maintain their appearance and optimum performance. UV radiation from the sun causes degradation and eventual damage to PVCu frames, which become brittle and powdery. Environmentalists state that damage to PVCu frames is extremely difficult to repair, resulting in replacement, where timber frames could simply be repaired.
No window system can be regarded as being wholly free from some basic maintenance requirements. Many features, such as the hardware, glazing and weather strips are common to all windows, irrespective of the material used for the frame and these require inspection and maintenance.
There are therefore many areas were timber has an environmental advantage in comparison to other materials. It is renewable and can reproduce to maintain an infinite supply and it is energy efficient, having low embodied energy, as well as good insulation properties. Trees play a major role in the world's carbon cycle, and forests store huge amounts of carbon.
Timber has been used to manufacture windows for centuries, albeit without a competitive alternative. The versatility of wood, as a suitable material for windows, is well established. The quality of the finished product has improved significantly as technology has advanced. Its sustainability is far superior to its competitors and it should be promoted accordingly to these benefits LAPFAG (2001). A feature sadly absent from much of the timber industry literature, which instead devotes a large amount of space to targeting the weakness of other materials.
Until recently, used PVCu profiles were taken to landfill sites and often left to degrade, this in its self caused environmentalist to raise concerns of lead based stabilisers leaching and contaminating surrounding areas. In recent years developments of alternative methods of disposal have been explored. A recent study by the BRE confirms that "PVCu can be successfully recycled (100%) several times over". Recovinyl, Europe's largest European recycler is a leader within this field and works closely with many of the main manufactures of UPVC. In 2010 Recovinyl recycled 250,000 tonnes of post-consumer PVCu, of which 49,343 tonnes came from the UK alone.
The main problem left with the recycled PVC fraction is colour matching and some impurities. This material cannot be used for the outer layer of the window. PVCu window profiles do allow the use of this technique, provided that the outer layer is virgin material, is at least 0.5mm thick and that the recycled material is derived solely from window profiles. Additives can be used, as necessary, to enhance the impact resistance of the material and to restore durability.