The ups and downs of life cycle thinking – Part Three
September 2016

In this third and final article focused on a review of the third report in the series “Towards Sustainable Cities”, funded by the International Aluminium Institute (IAI), we take a look at how recyclability, recycling and durability of window frames can be modelled, as each has a significant impact on Life Cycle Assessment (LCA) results. Environmental Product Declarations (EPD) based on LCA are increasingly used as the basis to quantify a product’s environmental impact during its lifetime in a building, making this something of a hot topic.

The report “Aluminium and Life Cycle Thinking” looks at the LCA results from using two different approaches for the recycling of window frames made from different materials: the Recycled Content Method (also known as the Cut-Off Method) and the End-of-Life Recycling Method (also known as the Avoided Burden Method). The former promotes the use of recycled materials; the latter promotes the production and preservation of recyclable materials. The “allocation” in LCA-speak, or how the benefits and impacts of recycling are attributed between products made with virgin or primary and recycled material, is a particularly tricky subject. Do you focus on the recycled content going into the manufacturing cycle, or the recovered material coming out? As you might imagine, there is much debate over which method is the most appropriate for LCA, and in practice different materials have different physical properties and market dynamics when it comes to recycling.

While the intrinsic value of some materials such as metals mean that at end of life recycling makes sense economically as well as environmentally, so that end of life recycling rates for metals are usually more than 90%, the increasing demand for these materials means that there is a limit to the relative amount of recycled material than can go back into manufacturing compared with primary metal, as demand outstrips supply. While the end of life recycling rate for aluminium in construction products is more than 90%, three quarters of all aluminium ever produced is still in productive use. So with 1.2 billion tonnes of primary aluminium produced since 1888, some 900 million tonnes are in products that are still in use, including the windows and curtain walling of thousands of buildings around the world. Aluminium in such long lifetime products have not yet reached the end of their “first life”. Two thirds of the primary aluminium produced since 1888 have actually been produced after 1990. We sometimes forget that aluminium is relatively speaking a “new” material, familiar only to the previous two or three generations.

The IAI report shows that in the case of window frames, the choice of allocation method has a significant impact on the LCA results. While aluminium is not considered to be the most damaging frame material when using the Recycled Content Method, when using the End-of-Life Recycling Method aluminium is clearly the least damaging in all of the impact categories assessed, including global warming potential and ozone depletion. As the report points out, the Recycled Content method which promotes the consumption and use of recycled materials essentially “encourages designers to play a global game of musical chairs, in which one project may demand higher recycled content in its aluminium supply, but can only do so at the expense of another project”. The End-of-Life Recycling Method encourages life cycle thinking, promoting the production and preservation of recyclable materials and asking designers and the whole supply chain to consider deconstruction and disassembly processes. When the frame alone will likely contain more than ten different materials, how can we better ensure that the design of windows facilitates disassembly and recycling?
It is this assembly nature of window frames, with different materials incorporated into the frame to serve distinct purposes and then subjected to a variety of operational stresses, including variable human usage factors, that also makes assessment of maintenance and durability difficult. In addition, most EPD are cradle-to-gate assessments that ignore the use phase entirely, partly to duck the issue. However, given the durability and low maintenance requirements of aluminium window frames, CAB believes that these factors must be considered from a building life cycle perspective.

The LCA approach can help here with different use scenarios. The report considers three different use scenarios associated with different maintenance regimes, from the conservative, based on manufacturers’ guarantees, to a high-maintenance regime where best practices are followed, such as an annual clean in the case of aluminium frames. Do the short term costs of maintenance pay back with longer service life? The results show a large variation in the results across the use scenarios and the report authors stress that further research is needed but for aluminium, the high-maintenance regime resulted in an approximate 50% decrease in some of the impact categories when compared to the conservative guaranteed service life scenario. In fact, this report shows that well maintained aluminium window frames prove to be the least impactful of the framing material options across all categories using the chosen scenarios, and that material reclamation and recycling at end of life is the most significant contributor to reducing the embodied environmental burdens of window framing products.