Plastic and Composite Windows - The Way Ahead




Text of a paper given by Dr Robin Kent at BRE/RAPRA Conference on "Composites and Plastics in Construction", November 1999

Part 1 - The market issues - Where is the market heading?

Part 2 - The technology issues - What are the critical technologies?

Part 3 - The materials issues: What are the materials choices?

Part 4 - The emerging driving forces - What will affect the whole market?

Part 1 - The market issues - Where is the market heading?

Windows, primarily manufactured from PVC-U, represent one of the largest markets for plastics in the European construction sector and one of the largest single markets for bulk polymers. In fact PVC accounts for over 90% of plastics extrusions in the profile and tube products areas for Europe. This category of "plastics profiles and tubes" excludes the usage of materials for pipe where the majority of the materials used are polyolefins (PE-HD, PE-LD and a variety of other similar products).

Total market volume 1,300,000 tonnes
(Source: AMI)

In 1998 the production of plastics profiles and tube products exceeded 1.3 million tonnes and nearly 90% was used in the construction industry with window applications using 56% of the total production (over 700,000 tonnes).

Total market volume 1,300,000 tonnes
(Source: AMI)

Other plastics materials used in construction profiles include PE, PP and PS but these are all minor in comparison to PVC-U in the sector as defined.

The average annual volume growth for PVC applications is forecast to be 4% for the next five years and PVC is here to stay as a material in construction and window applications. On a European scale PVC-U windows accounted for 37% of all the windows produced in 1998, whereas in the UK this was doubled and PVC-U accounts for approximately 75% of the total windows produced. This does not mean that the market is stable and new materials are now appearing that could challenge, or at the very least change, the dominance of PVC-U in the manufacture of window frames.

1.1 The market sectors and the strengths

The UK market growth for PVC-U windows in the 1980s and 1990s was both significant and rapid. From a market penetration of almost zero (with similar consumer confidence) in 1980, the market has grown such that in 1999 the overwhelming bulk of domestic replacement windows are manufactured from PVC-U and it is the first material that consumers think of when discussing "double glazing". In fact, "double glazing" is almost synonymous in the consumer mind with PVC-U. As an industrial case study, the industry is a classic tale of a good product and exceptional marketing. The market is now reaching a crossroads in development terms and is rapidly approaching maturity. This opens up serious discussions about "The way ahead" and the way the industry will approach the future.

The market structure

The PVC-U window market is an aggressive sales market, as we all know, and the industry is closely focused on today's sales rather than on specific developments for the future. Long term planning in the market largely consists of solving the reason for losing today's sale. The market is highly consumer driven and because almost all PVC-U windows are made to order it is highly customer focused. The market structure in the UK and Europe is still young (less than 25 years in the UK) it is very distinct and is rapidly changing as consolidation takes place. The structure is outlined below.

 The domestic market

PVC-U dominates the UK domestic replacement window market and is the material of choice for most homeowners. Whilst strong regional differences are evident, a national average of approximately 80% of replacement windows installed were PVC-U. The majority of these were installed for complete houses.

Over 80% of the windows being replaced are timber with approximately 8% and 10% being aluminium and steel respectively.

The rate of replacement is now so high and so rapid that several questions must be asked by the PVC-U replacement window industry. The most important of these is what happens when there are no more timber or aluminium windows to replace?

The new build market

Having effectively dominated the replacement window market for nearly 10 years PVC-U manufacturers sought new markets in the early 1990's. An obvious target was the remaining stronghold of softwood windows - the new build housing market. Softwood windows had dominated this market for many years and there were several technical and cultural barriers to market entry. These were:

The rapid development of window former systems which act as cavity closers and window acceptors improved the installation times and allowed PVC-U windows to be delivered "ready to fit" to the site. PVC-U manufacturers also began working with the larger builders and in 1999 over 75% of PVC-U windows were fitted by the suppliers for the builder.

These technical improvements coincided with:

The market share of PVC-U windows has grown rapidly and larger housebuilders (those building over 500 houses per annum) have largely overcome the technical and cultural difficulties to make the leap to having PVC-U windows installed. In 1998 82% of windows installed in new houses by larger housebuilders were PVC-U but this dropped to a penetration of 42% for the smaller builders. To quote the phrase "size does matter".

As with many changes in the construction market the cost is a significant driving force and in 1998 the average installed price for PVC-U was approximately 1 less than that for softwood windows.

One change in the market is that the large builders expect the windows to be installed by the supplier, thereby contracting out the complete window installation section of the work.

This does not mean that the softwood window is dead and buried because work by the British Woodworking Federation via the Accredited Window Scheme has greatly raised the quality and performance of wooden windows. The market is not static and changes in the pattern are expected in the future. Factory finished high performance coated wooden windows are predicted to retain a significant share of the market and even to grow at the expense of other materials.

The rise of PVC-U in the new build market raises the question of market saturation again. If the windows being initially installed are PVC-U, then where are the windows to be replaced tomorrow going to come from?

The commercial market

The commercial market is very hard to define and the penetration of PVC-U into this market is also hard to define. For simple replacement windows, such as flats and commercial buildings where the windows are installed into an aperture, the penetration of PVC-U is high and increasing on a daily basis. For more complex buildings, such as those that involve curtain wall types of structures, PVC-U has made little impact. The need for PVC-U to have reinforcement and supporting structures means that aluminium systems are still dominant in this sector and are unlikely to be replaced by PVC-U in the near future.

1.2 Current capacity for plastic and composite windows

The current market capacity for PVC-U far outstrips the demand and significant consolidation is taking place daily at all levels of the supply chain. It is conservatively estimated that the over-capacity exceeds 40% at virtually all levels of the industry. The market demand is also forecast to decrease significantly as the bulk of the windows suitable for replacement are replaced - the future for the industry is one of excess capacity and shrinking demand unless new strategies and growth areas are found quickly. The effects of over-capacity rapidly become critical as soon as demand is reduced!

Consolidation of the industry

Consolidation of the industry is taking place at a rapid rate and approximately 30% of the building profiles market is accounted for by just 10 leading extrusion organisations, such as the large continental companies Veka, Kommerling, REHAU and Deceuninck and the rapidly growing Heywood Williams group in the UK. Many of the major systems suppliers are either for sale or have been sold, merged or closed in the last 12 months. The same consolidation pressure is rapidly making itself felt at the fabrication end of the market.

The price pressure in the industry is intense and in 1999 prices in the market are down to 50% of the early 1980s prices, even ignoring the effect of inflation. In real terms the prices have dropped to below 30% of the prices achieved in the early 1980s and the product being sold for these prices has improved in terms of security, manufacturing quality and performance.

The driving forces of competition for market share, changing consumer behaviour and over-capacity have combined to reduce considerably margins. The industry response has been to improve manufacturing techniques, improve management skills and to look for economies of scale. In the early 1980s a large window manufacturer was making 200 windows per week - now a large manufacturer (the super-fabricators) are making 2500 windows per week and growing bigger. The largest of these claim to have capacity for up to 10,000 windows per week but it is doubtful that they are really filling the total capacity. The growth of the super-fabricator is such that they regard their potential customers as fabricators who currently manufacture 200 windows per week, the large window fabricator in the 1980s. There is still growth in the market as a whole and for individual fabricators but the market will never return to the growth and price levels of the 1980s.

Consolidation is likely to continue because the long-term erosion of real price levels has reduced profitability and capacity has outstripped demand.

Part 2 - The technology issues - What are the critical technologies?

2.1 Industry Issues

Several technology issues, both current and future, will affect the market and the product (independent of frame material). The two most important current issues are security and standards.


Increased security requirements (and the increased consumer demand for secure products) have changed both the design and manufacturing methods used for all window products and have had even more impact on the hardware suppliers to the industry. The major driving forces for this were rising consumer concerns about crimes against property and the fact that in most burglaries entry was achieved via windows and doors. This was amplified by increased promotion given to the "Secured by Design" initiative and by Crime Prevention Officers who had needed guidance to give consumers in the choice of windows and doors with improved security properties. The collaborative industry development of the Product Approval Scheme PAS 011 and the later transition of this into the British Standard BS 7950 for "Enhanced Security of Windows" provided a method for independently assessing the security resistance of windows and doors

The production of the standards curbed the wilder claims of some sectors of the industry regarding burglar resistance and accelerated the development of window systems and hardware to meet the standards. Systems were changed or developed to allow "internal beading" and hardware was greatly improved to meet the new standards. With this development the industry itself changed and the traditional externally beaded PVC-U window rapidly became a minority in certain areas rather than a majority as previously.

The total cost of improvements to meet the security requirements would be conservatively estimated to be in the region of 30 million and the cost is still rising. Despite this consumer prices remained largely unchanged.

As a contrary note to the whole "security" debate it is noteworthy that:


The PVC-U window industry has, for many years, been exceptionally standards and specification conscious, despite (or perhaps because of) what is published in the press. The industry has worked hard to create and implement standards across a wide range of products and processes. The industry associations, notably the British Plastics Federation Windows Group (BPFWG), have largely driven this process, and many of the BPFWG Trade Standards have been translated into British Standards.

This standards process has raised the quality and consistency of the product and processes in an extremely competitive market but for some companies it has become a "rod for their own back". One company has ten Kitemarks and is actively seeking two more - at a cost of anything up to 20,000 to achieve a specific Kitemark and annual running costs of up to 5,000 per Kitemark this is a significant investment in the standards process. The industry costs are very significant and there are indications that some companies are no longer prepared to pay the costs. After all, "certification is a game to be played between consenting adults".

The table below shows the number of Kitemarks issued to PVC-U companies for the relevant standards compared to those issued to aluminium and timber window companies for the relevant standards. It is relevant to note that achievement of a Kitemark for any specific standard automatically requires attainment of the relevant ISO 9000 standard.

Kitemarks™ issued (as at April 19, 1999)

Standard Number




BS 7412

White PVC-U window fabrication



BS 7412/7950

White PVC-U windows/security



BS 7413

White PVC-U profiles - systems



BS 7413/7950

White PVC-U systems/security



BS 4873

Aluminium windows



BS 4873

Aluminium windows/security



BS 644: Part 1

Timber windows



BS 644/7950

Timber windows/security



The investment of the PVC-U window industry in the attainment of standards is significant both in terms of initial and maintenance costs. This has not generally been passed on to the consumer in any way and certification to standards is now accepted as part of the cost of staying in the market.

Work has been taking place in Europe for many years on the production of EN standards for windows and related products and it is only now that the impact of the EU and standards harmonisation is starting to be felt. The work of the early 1990s is coming to fruition and the pace of issued ENs is increasing. These are replacing the current British Standards and are starting to have an increasing impact in both design and specification. This will have large (and potentially costly) effects on both the design and production of PVC-U windows in the UK.

One particularly important area is in the wall thickness of the PVC-U profile. Windows in the UK tend to be smaller and broken into more sections than windows on the Continent. This means that they do not require the same wall thickness of PVC-U to function correctly. Despite this, the Continental consensus is that wall thickness should be specified in the EN for PVC-U windows, even if only as a grading mechanism. This simple "prescription" based approach to the standard (rather than a "performance" based standard) will potentially cost the UK industry more than the security issue and with no real benefit to the consumer.

Part 3 - The materials issues: What are the materials choices?

3.1 The ideal window material

The ideal window material has the following characteristics:

Existing frame materials meet many of these requirements but there are still areas for new materials developments to meet specific applications and needs. The market is not static and there is still the possibility of a "new PVC-U" which will change the complete market structure.

3.2 The existing materials


A SWOT analysis for PVC-U is given below to examine the potential for the future:




  • Low maintenance load but not maintenance free!
  • Unaffected by moisture.
  • Good thermal insulation.
  • Lightweight.
  • Easy to machine and process.
  • Highly certified/accredited industry.
  • Low mechanical strength.
  • High thermal expansion.
  • Over capacity of sector and fragmentation at all levels.
  • Decreasing gross margin at all levels.
  • Volatility of raw materials costs.
  • Structure of industry.



  • Increased penetration of new build sector.
  • Rapid fitment methods.
  • Wide range of styles.
  • New finishes to provide colour options.
  • Small scale curtain walling applications.
  • Retail replacement market slowing due to saturation and slow housing market.
  • Volatile raw material prices.
  • Fragmented market at all levels with emerging signs of consolidation.
  • Extreme price pressure at all levels of market.
  • Environmental pressure on the use of PVC-U as a material.


The timber window industry is undergoing a renaissance due to dynamic initiatives to regain market share in the sector and this is being lead by the British Woodworking Federation through their Accredited Window Scheme. Some pressure groups also see the wooden window as being more "environmentally friendly" and "architecturally sensitive".

For timber windows there are two important sectors i.e. the softwood sector which provides volume products and is under severe attack from the PVC-U sector and the hardwood sector which continues to be strong and a material of choice for high cost and prestigious buildings.

A SWOT analysis for timber windows (both sectors combined) is given below to examine the potential for the future:




  • Well known and traditional material.
  • Low perceived cost (at first installation).
  • Stable and well established supply chain.
  • Easily modified on site.
  • Good thermal and sound insulation.
  • Easy for end-used to repair and maintain.
  • Doors have high consumer appeal and traditional base.
  • Appearance can be modified by consumer
  • Higher maintenance load for end-user if not treated correctly.
  • Expands and contracts due to the presence of moisture and can give interference problems.
  • Industry is under attack by alternative materials, is in general decline and activity is low.



  • Private sector housing and extensions have always provided volume usage.
  • Improvements in surface coating techniques to reduce maintenance loads.
  • Use of composite materials / layer techniques to give lower cost, more efficient materials usage.
  • Surface coatings applied in factory to give factory finished products ready to install.
  • Continued growth of alternative materials in new build sector.
  • Materials price increases for both types of raw material.
  • Sustainability issue and environmental action for tropical hardwoods.
  • Price decreases for alternative materials (at first installation).


The steel window industry is not currently based in the domestic sector but concentrates mainly in the commercial sector where the particular mechanical strengths of the product are best utilised.

A SWOT analysis for steel windows is given below to examine the potential for the future:




  • High mechanical strength.
  • Slim sight lines due to exceptional mechanical strength.
  • Excellent fire resistance in conventional tests.
  • Low thermal insulation unless used in combination with other materials.
  • High maintenance load after initial coating.
  • Transport difficulties
  • Small supplier base.
  • Difficult to make bespoke products.
  • On-site modification is difficult.



  • High strength gives excellent security and mechanical response.
  • Door products using high mechanical strength to advantage i.e. composite doors.
  • Commercial work presents best opportunity.
  • Thermal assessments may prove surprising for new ranges of windows.
  • Continued inroads by alternative materials.
  • Fashion moving away from steel as framing material.


Aluminium has an inherent corrosion and rot resistance and was the first of the new window framing materials. Although the product has been in use for many years (it was used for spandrel panels and storefronts on the Empire State Building in 1929) the period of rapid growth began in the 1970’s with the development of the domestic double glazing market. Aluminium has suffered by the development of the PVC-U market and most domestic work has been replaced by PVC-U. A notable exception is the London area where aluminium continues to be strong in domestic replacement windows.

A SWOT analysis for aluminium is given below to examine the potential for the future:




  • Low maintenance load but not maintenance free!
  • High inherent corrosion resistance.
  • Lightweight products.
  • Fire resistance.
  • Good security results.
  • Recyclability of raw material.
  • High mechanical strength allows curtain walling and commercial applications without additional reinforcement.
  • Raw material costs.
  • Low thermal insulation unless thermally broken or clad with additional materials.
  • On-site modification is difficult, difficult to work with once fabricated.



  • Composite windows with good thermal properties and attractive finishes.
  • Curtain walling and large commercial structures in coloured products.
  • PVC-U has mainly taken domestic market and commercial market is now being threatened by the development of PVC-U based curtain wall structures (for small developments only).
  • Revival of wooden windows (with improved surface coatings).

 3.3 The new materials

The future for most of the alternative materials is in a state of flux as new materials are developed or older technologies see the window industry as a target for applications.

All new products, including window frame materials, fall into the S-curve concept of product or process development. This concept states that every technology follows an S-curve; initial developments are costly for little real improvement in operating performance and the initial performance may actually be less than that of the existing technology in some important respect. As times passes the new technology enters a region of development where improvements achieved are very cost-effective and the performance overtakes that of the existing technology. At the end of the cycle the cost of developments increases for small improvements actually achieved and a new technology is developed.

Many of the new window frame materials are at the lower end of the new technology development curve and are ready to experience the rapid growth section, provided they are able to achieve the critical mass and the necessary route to market. This is not an easy task given the current structure of the window market.

The development costs and polymer chemistry make it unlikely that any simple new bulk polymer will be developed and used for window frame applications. The key developments are those using low cost fillers to marginally stiffen and fill the matrix or high cost reinforcements to greatly stiffen and reinforce the matrix. The structure of the market makes penetration by new materials difficult but a variety of new materials are now appearing to present the market with a range of options.

Pultrusion: Resins and glass fibres

One of the most promising of the newer materials processes is pultrusion. The process has been investigated many times over the past 20 years but is yet to achieve a strong market commercialisation in the window frame area. The extremely high dimensional stability, low thermal conductivity, high corrosion resistance, high modulus and colour possibilities make pultrusion a good candidate for some window applications.

The main disadvantages are high cost, low workability (all corners must be mechanically jointed) and the previous difficulty in producing the fine surface details needed for some profiles. These disadvantages have not stopped the development of window and patio door systems in both the UK and USA and products from this material will continue to be developed for products where the advantages offered far exceed the disadvantages. The cost of the pultrusion itself may be higher than an equivalent length of PVC-U but the high stiffness means that no metal reinforcement is needed and this effectively reduces both the raw materials and labour costs for the final product.

An alternative to the standard pultrusion is the Owens-Corning process of CLM (continuous lineal moulding) which is pultrusion over an insulating core of dense glass fibre wool. This process greatly improves the thermal response of the product whilst maintaining all the other advantages of pultrusion.

Potential applications are for windows and similar products where high stiffness properties, high load bearing properties and extreme chemical or thermal inertness are required.



  • Extremely high dimensional stability
  • Low thermal conductivity
  • High corrosion resistance
  • High modulus
  • Colour possibilities
  • High perceived cost
  • Low workability
  • Some difficulty with fine surface details
  • Surface finish

A process with great potential for window and door applications where the high stiffness greatly improves the product characteristics.

Thermoplastic pultrusion - PVC-U and glass fibres

A recent PERA Craft Project (BES-5202) involving a consortium of UK, German and Italian companies has resulted in the development of a "PVC-U extrusion locally stiffened by continuous glass fibre" and patents have been applied for the resulting process and products. This product uses a localised glass fibre reinforcing encapsulated via co-extrusion into a PVC-U matrix. The localised glass fibres allow the precise placement of the fibres to obtain a high modulus composite with the glass fibres adding the strength and the PVC-U providing the matrix. The PVC-U enables details and surface finishes to be formed similar to conventional extrusions and the technology is essentially that of extrusion.

The product cannot be structurally welded as with standard PVC-U because of the presence of the glass fibres but a cosmetic weld is said to possible. Mechanical strength requires additional fastening.

Potential applications include conservatory roof bars and similar products that do not require welding to form a frame structure.



  • Localised glass fibres give high stiffness and high modulus
  • Conventional PVC-U surface details possible
  • Conventional process technology
  • Other properties as per PVC-U
  • Cannot be structurally welded
  • Development project only with no commercialisation at this stage

A process with great potential for specific projects such as conservatory roofs and similar products.

Polystyrene based materials

Extruded polystyrene structural foams, such as "Polywood" (and other earlier types such as "Timbron"), have frequently been proposed as possible window frame materials. These materials have a good "wood like" finish and have advantages such as a workability similar to wood, low cost and the ability to be produced on conventional single screw extrusion lines.

The greatest disadvantage is the fire response of the product, adding fire retardant to the product improves the fire response and the material can achieve Class 2 of BS 476: Part 7: 1987. The material will, however, "drip and burn" when subjected to real flame testing and this may restrict the potential for window frame applications.



  • Good workability
  • Low cost tooling and processing
  • Wood like finish
  • Concerns with fire response
  • No successful commercial window applications known to date

A process that has been in existence for some years and current products suffer from the experience of poor performance with earlier similar products.

ABS based materials

GE Plastics have released and promoted the use of ABS as a window frame material, this product also uses an ASA co-extruded outer layer to improve the weather resistance to usable levels. Despite the current price difference between PVC-U and ABS/ASA, GE has claimed that the ABS/ASA composites can use much the same production machinery but the products can be thinner walled, run faster (30-40% faster) and have better physical properties than equivalent PVC-U products.

The process has been developed and tested with trial products in the USA but little progress has yet been made in Europe with these materials.



  • Light weight
  • Conventional process technology but runs faster than PVC-U
  • Lighter weight than PVC-U for same stiffness
  • Good surface finish
  • Higher cost than PVC-U
  • Needs ASA layer for UV and weather resistance but ABA gives exceptional performance as surface
  • Cannot be structurally welded

A conventional process using a newly developed material and technology in an attempt to enter the window market. Probably matched in all benefits by other materials which are better established and cheaper.

PVC cellular products

Cellular PVC (PVC-UE) has long been used in the UK for many types of trim and finishing applications but is now being used in the USA for main frame window products. The products can be treated like wood (nailed, planed and screwed) but have many of the properties of PVC-U with regard to corrosion and fungus resistance.

The cost is low, the mechanical properties good and the technology is common with the existing extrusion technology.



  • High thermal efficiency
  • Can be nailed, screwed and treated as wood
  • Conventional process technology
  • Other properties as per PVC-U
  • Cannot be structurally welded
  • Lack of detailed surface features
  • Price may be a disadvantage

A process already used for “roofline” and trim products but not yet used in the UK for full window and door systems. Good possibilities for the future.

Plastics and biological material composites

New materials are being developed in this area and cover a wide range of polymer matrix types as well as a wide range of biological fillers and stiffeners. The plastics used include PP, PE and PVC and the fillers used include wood flour, flax, jute and other cellulose based fibre fillers. The range of materials used is wide and only a summary can be attempted in this short paper. The high wood flour content of some products (up to 70%) may lead to some confusion in the market - is it wood or is it plastic? The wood and plastics window industries may not only reach an accord but also come together in a more intimate sense as wood product companies transform themselves into composites companies.

The majority of the current work being carried out is in the USA where significant advances are being made and finished products are already being released onto the market. As yet there is little commercial activity in the UK but this will undoubtedly come as the benefits of the materials are recognised in the UK. The market in the USA is also made more difficult because of ongoing patent disputes over various aspects of the technology and this makes reliable information on the exact technology difficult to obtain.

In some cases the producers are existing timber window manufacturers who have access to large quantities of sawdust and scrap wood products suitable for treatment and inclusion in this type of product. This means that no wood resources are depleted in producing the products and wood waste disposal concerns are removed. The sources of the base plastic vary but range from recycled PE bags to recycled PP battery case materials. The recycling ethos is employed in these products to use materials from short life cycle applications in long life cycle applications.

One of the major barriers to development is the difficulty in combining a hydrophobic material (most plastics) with a hygroscopic and hydrophilic materials (most cellulose based fibre products. This results in difficulties in compounding of the materials and poor stress transfer characteristics of the combined products. The general technique is to use a "compatibiliser" or "coupling agent" to improve the blending of the products and the interfacial interaction of the two phases. A typical compatibiliser is maleic anhydride modified polypropylene (MAAP) which can be used to treat polyolefins and cellulose products to give improvements in the processability and mechanical strength of the final product. The exact content of most compatibilisers is confidential and MAAP is generally not the only agent used in the compound.

The PE based products are cheaper have a higher heat distortion temperature than PVC based products but the PVC products do not suffer form the low surface energy of the PE products which makes painting and post-treatment difficult. In both cases the cellulose products improve extrusion speeds because of the higher heat transfer rates from the cellulose materials.

These composite products can generally be nailed, painted and otherwise treated as wood whilst retaining many of the benefits of plastics in the areas of fungus and corrosion resistance.

Cellulose based materials reduce costs, increase production rates and offer a host of benefits to the profile production.

CertaWood - CertainTeed

CertaWood is a coextruded wood-plastic compound that can be stained painted and is marketed at slightly higher prices than conventional PVC-U windows. This product uses a PVC core with a wood-PVC extruded outer layer to give the decorative and handling characteristics of wood products. The company generates all wood for the process from other operations.

Fibrex - Andersen Corp.

Andersen launched their first wood-fibre reinforced PVC profiles in 1993 under the name of Fibrex. This is a base of wood filled plastic with a virgin PVC outer layer coextruded onto the core. The approximate ratio is 60% PVC-U and 40% wood fibres generated by the company from other operations.

MikronWood - Mikron Industries

This is available in two formats: a high density PVC alloy with 10-70% wood flour content and a low density product with a foam interior. The product is run on standard PVC-U processing equipment but the stiffer product gives faster processing speeds. The high wood content has lead some fabricators to market the products as "wood windows", the opportunity for confusion is immense!

Comptrusion Corp.

Produces products based on the Strandex licence and makes window and door profiles using hardwood and softwood flour in PE and PVC. These generally have a coextruded outer layer of PVC.

TimberTech - Crane Plastics

This is a 50% wood-filled PE-HD profile used for decking and windows and doors parts.



  • Low cost and plentiful raw materials
  • Recycled raw materials
  • Hybrid materials - combine the best properties of both the biological materials and polymers.
  • Good stiffness
  • Compatibilisers raise costs
  • Affects all current technology investments
  • Need to learn how to handle new materials (powder and dust)

These may well be the “new composite materials” for windows with a wide range of features and benefits. Plethora of processes and patents may well restrict development until the market settles down.

What now?

Low cost materials in this area will revitalise the industry and give a huge advantage to the first companies to develop the products. Many companies in the UK are not developing products purely because of their current investment in existing technology. This will change in the future as low cost materials enter the market and compete against the existing materials. Staying in a particular technology simply because of your investment in the technology is not a recipe for success in any fast moving market and the window market is no exception.

Part 4 - The emerging driving forces - What will affect the whole market?

The earlier driving forces for rapid market expansion largely related to individual decisions by domestic owners to choose low maintenance materials in preference to higher maintenance materials. The purchases were classic "distress" purchases and this influenced the consumers view of the market. In the future new driving forces will emerge and these are predicted to be:

4.1 Environmental issues

The increasing pressure from environmental groups against PVC-U and hardwoods as materials is starting to have an effect in the market. This pressure will continue to grow in importance for as long as the industry continues to respond to the criticisms in the current method. A new strategy is needed to convince the consumer and government that the materials, when used correctly, are both safe and environmentally benign.

The current pressures on PVC-U are considerable. The basic scientific information shows that PVC-U is a safe and reliable material that can be recycled and is environmentally benign. This is not making a real impact in the perception of the product because some groups would rather deal in spurious arguments and half-truths than in facts.

Measurement and regulations

There is currently no legislation in this area other than the standard waste disposal acts and the environmental protection acts that every industry must comply with. There are sporadic incidents of Local Authorities taking a position against PVC-U for a variety of reasons but the British Plastics Federation or other interested groups deal these with on a local basis.

Life Cycle Analysis (LCA)

There is much ill informed criticism regarding the suitability of PVC for use in windows and other building products. The claims of certain environmental groups, particularly Greenpeace, are based largely on emotional arguments regarding PVC and chlorine - the "devil's element".

LCA studies on window profile materials by Novak and Ecker compared PVC, aluminium and wood as window frame construction materials and concluded that there was no basis for recommending any particular material on environmental impact grounds. Any firm conclusions on environmental impact required an analysis of the specific requirements of the application.

Some key points of these and other reports are:

The future

The environmental criticism of the use of PVC products in either short or long term applications appears to be the product of emotion rather than science. Similar environmental pressures are being felt for hardwood in terms of managed forests and destruction of the rainforests.

The environment will continue to grow in importance but the benefits of correctly designed windows in reducing energy usage need to be publicised.

4.2 Energy Issues

The increasing concern regarding the energy consumption and CO2 generation that relates directly to the use of windows with a low energy efficiency. Windows are often only seen as a source of energy loss from a house and the current Building Regulations serve to reinforce and codify this attitude. In reality windows can provide a net energy gain to a dwelling and this needs to be accepted and utilised in both the design of windows and houses. Energy rating of windows to consider the overall effect of the window on the energy usage of housing will be an emerging driving force in the selection of windows. This concern with energy efficiency is seen in the new proposals for the Building Regulations but even the new Regulations continue to make the same erroneous assumption of windows being a "loss only" element of the building fabric.

Initial selling of PVC-U windows in the UK concentrated on the reduction of heat losses and the energy savings possible from this. With the fluid housing market in the UK and the pay-back period involved the person who has the windows fitted is rarely still the occupier by the time the windows have returned the investment. For this reason the sales strategy turned to the low maintenance and away from heat losses. Despite this, most purchasers acknowledge that PVC-U and double-glazing reduces energy bills and improves the comfort of the house.

The current Building Regulations have a very basic approach to thermal transmission and set a simple maximum U-value requirement for each component and then link this to the allowable area for the component. For windows, roof lights and doors the requirements are satisfied if the average U-value of 3.0 or 3.3 is linked to an overall area of glazing not exceeding 22.5% of the floor area of the dwelling. The essential point is that double-glazing becomes the minimum acceptable glazing method for new buildings. This current U-value of 3.3 is very high in comparison to European levels where much lower values are required and there are significant efforts being made in the UK to reduce this to the 1.5-2.0 level.




The energy flow in a window consists of three major components - the solar heat gain (SHGC) in the form of radiation, the non-solar heat losses and gains from conduction, convection and radiation of all of the components of the window (not simply the glass) and airflow through the window both designed (ventilation) and unintentional (infiltration).

The thermal losses from a building are not simply the losses from the glazing (although this is a major loss area) but also from air infiltration and losses through the frame. The frame contribution is currently ignored whatever the material.

Windows have been traditionally regarded as energy losers and current Building Regulations encourage this viewpoint by only looking at the negative or loss aspects of windows. Windows can actually add energy to the building system and this is easily proved - sit in front of a window on a sunny day and the sun's radiation will instantly warm you. The window is gaining energy from the solar radiation! Yet when the current Building Regulations consider windows they ignore the solar heat gain and concentrate on entirely the energy losses - this about as sensible as trying to assess how fuel efficient a car is by looking at the weight of the car! The inclusion of a Solar Heat Gain Co-efficient (SHGC) into the effect of windows on buildings will radically change the way we calculate the energy efficiency of buildings and can lead to larger windows being used in building.

The energy and CO2 issues

The current Government, as part of the Kyoto, agreements, has pledged to reduce CO2 emissions by 20% by 2010. Buildings use 50.5% of all energy in the UK and 34% of all energy used in the UK is used in housing. This high energy use means that domestic housing creates twice as much CO2 as cars (40 million tonnes from housing as compared to 20 million tonnes from car usage) and creates over 30% of the CO2 emissions in the UK. CO2 savings are very much on the Government agenda!

The Government is putting considerable amounts of money into reducing the energy use of buildings and this is being channelled via the Energy Saving Trust and a range of energy saving measures and projects. One of these is the British Fenestration Rating Council (BFRC) PIT project part-funded by the Department of Environment Transport and Regions (DETR). This project aims to create a system for the energy rating of windows based on the successful schemes already established in the USA, Canada and Australia. This will probably be a simulation based system rather than a hot-box based system to reduce the manufacturers costs. Full details are available on the project Web Site located at This will have an impact on the materials and design of frames because for the first time it will be possible to directly compare the thermal efficiency of the complete window unit for various manufacturers and materials.

Proposals for action at government levels

There is considerable pressure on the Government and other advisory bodies involved with the Building Regulations to change the current regulations at the earliest possible opportunity. Typical proposals are:

Other groups are working to tax energy saving materials at the same or at lower rates than energy. Currently VAT on domestic energy is at a reduced rate and yet VAT on energy saving items is at the standard rate - if the government really wants to save energy then this will be a very powerful driving force (as with the drive to convert cars to unleaded fuel).


The way ahead for plastic and composite windows is not a simple one. A combination of market forces in the shape of security, standards and increased environmental pressures will meet an industry struggling with low margins, consolidation, new materials and a decreasing market. It may not be a rosy future but it will certainly be interesting.


Last edited: 20/05/15

Tangram Technology Ltd. 1999

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