When builders now consider more modern replacements for window frames, they often plump for one of aluminum's main rival – uPVC. For overall clarity, PVC (short for polyvinyl chloride) is a plastic commonly used in construction and building materials. Plasticizers make it more flexible so it can be used to form pipes. It's also used as an insulator for electrical cables. There are some concerns about toxins and radiation, and three of the chemicals used in PVC have been banned by the EU.
uPVC is polyvinyl chloride without the plasticizers. It remains highly durable and stays rigid instead of flexing, making it a common wood replacement. It's also fire resistant and recyclable. It also lacks any serious toxins or radiation—the chemicals used to transform it into PVC are what create the toxins. The characteristics of PVC used in windows vary, since the additives play an important role in the properties of the end product and there have been many advances in material formulation. Additives can be plasticizers to reduce brittleness and improve processing, or stabilisers to protect against degradation caused by heat, oxidation and solar radiation.
Aluminium is produced from its abundantly available ore, bauxite. Primarily, aluminium production requires a great deal of energy and it generates huge amounts of environmentally dangerous pollutants like carbon dioxide, acidic sulphur dioxide, along with polyaromatic hydrocarbons fluorine and dust.
Aluminium can be recycled repeatedly with virtually no deterioration in quality.
Recycling aluminium requires only about 7% of the energy needed for primary aluminium production from its ore.
A standard window (1.2m × 1.2m) has been evaluated for its embodied energy with aluminium and PVC. It has been found that the aluminium windows consume the highest amount of energy equal to 6MJ, while uPVC windows have their respective embodied energy equal to 2980 MJ.
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 as building materials (aluminium in construction was used for spandrel panels and storefronts on the Empire State Building in 1929) the period of rapid growth began in the 1970s with the development of the domestic double glazing market, the development of a thermal barrier to insulate the aluminium window frame and interrupt the heat flow between the exterior and interior surfaces to substantially improve the windows performance and further aid its acceptance. uPVC has led the way and been developed for mass production. This has kept prices relatively static, if not lower over time if you take inflation into consideration.
Aluminium has suffered by the development of the uPVC market and most domestic work has been replaced by uPVC. For simple replacement windows, such as flats and commercial buildings where the windows are installed into an aperture, the penetration of uPVC is high and increasing on a daily basis. For more complex buildings, such as those that involve curtain wall types of structures, uPVC has made little impact. The need for uPVC to have reinforcement and supporting structures means that aluminium systems are still dominant in this sector and are unlikely to be replaced by uPVC in the near future.
In the window frame sector, aluminium, along with the innovative polyamide thermal break profiles, has managed to win market share away from uPVC in some national European markets, although uPVC use continues to rise in other countries such as France.
For example, countries like Spain or Italy in past showed the market share of aluminium windows over 70 – 80%.
Now aluminium is losing it's position to uPVC windows.
uPVC performs extremely well in terms of sustainability. uPVC is extremely resource-efficient in its manufacturing and creates windows that offer excellent thermal performance over a long lifetime, although the frames may potentially degrade over many years and aluminium, however, is a much more prosperous compound and with proper care will stand the test of time without compromise. Approximately twice as much heat loss occurs when you install aluminium windows in your home compared with that of uPVC joinery using identical glass. uPVC windows are an excellent insulator, reducing your heating and cooling bills by preventing thermal loss through the frame and sash material. This is not because uPVC is actually warm, but because uPVC is an excellent insulation material - it leaves the heat in the room where it belongs. Conversely, aluminium is an excellent conductor of heat - it draws the heat from your home and dissipates it to the surroundings.
On the other hand, uPVC windows are stable in saline and polluted air, while they have high coefficient of thermal expansion (two to three times higher than aluminium). PVC is very sensitive towards high temperature and ultraviolet (UV) radiation, which can break its molecular bonds, resulting in embrittlement and discoloration.
In addition, when uPVC frames are eventually replaced, they are easier to collect and replace, but the recycling of uPVC is a complex procedure due to the presence of associated polymers and reinforcements materials.
uPVC will not change shape under normal weather conditions, but it can be reshaped at very high temperatures. If left unattended, uPVC decomposes very slowly and as a waste product it contains environmentally dangerous substances that can seep out into soil and ground water.
Aluminium being a highly conductive material, more than 1000 times more than PVC, condensation forms on the frames as well as the glass. Condensation on aluminium is a common nuisance for many – because of the development of mould in the corner of the windows, but aluminium is chemically much more robust and stable. If bought with polyamide thermal break profiles, it stands for extremely energy efficient aluminium windows, doors and facades.
Let`s put it this way –because of its low thermal conductivity, the uPVC profile helps avoid condensation and mold on unattended windows, but in regards to flexibility, architectural design, color personalization, stability, price and life expectancy (Surveys show that aluminium windows can easily last more than 40 years and PVC windows, in most cases, are reported to have an optimum service life of 25 years), aluminium, arguably, has surpassed uPVC in the benefits and choices it offers.