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Sustainable Windows Study

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Sustainable Windows Study

Reading Time: 5 Minutes
Published on: March 18th, 2021

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Many sustainable windows manufacturers may claim to produce environmentally friendly products, Gowercroft among them. We have worked very hard to ensure that our workshop and products have as little effect on the environment as possible.

An Independent Study on Sustainable Windows

In order to find out exactly what impact our products have on the environment and how we compare to the window manufacturing industry as a whole, we commissioned a study with Dr. Stuart Walker CEng MIMechE at the university of Derby. We asked Dr Walker to find a credible way of measuring the environmental impact of our products, and also to run a comparison to other manufacturers.

The research was to be totally independent and unbiased. The point of the experiment was to measure our own success in a genuine and honest way. We needed to know what we had achieved in our goal to make sure that our products really did support a sustainable process. In finding this out we could see any areas where we could improve our performance.

After extensive research Dr Walker came back with two detailed reports on his findings. The first is a comparison between the three different Gowercroft products and three products in other materials – Wood, Aluminium and uPVC. The second report is specifically about three Gowercroft products.

How to measure a windows environmental impact

The first job was to identify exactly how to measure the test. Dr Walker concluded that the environmental impact of the products was derived from “the raw materials, material extraction and manufacture of the product, the transport and packaging of the product, its lifetime of use, and the treatment of the product at the end of this life.” Dr Walker conducted what’s called a Life Cycle Assessment based on each of the impacts.

Life Cycle Assessment

There are 2 Life Cycle Assessments – 

  1. ‘Cradle to grave’ assessment includes the full lifetime of a product, from raw materials to end of life. 
  2. ‘Cradle to gate’ assessment considers the product only from raw materials to departure from the hypothetical factory gates, and excludes the transport of a product from the manufacturer to the user, the installation or use of a product, or the end of life.

Life Cycle Assessment considers a wide range of environmental impacts, including Greenhouse gas emissions (commonly known as carbon footprint), which is arguably the most important impact, and is the one presented here.

Because a Cradle To Grave study would not have data for all the products – no Gowercroft windows have reached the end of their service life yet – the study was to be based on the Cradle to Gate assessment. It is worth noting that the predicted service life of Gowercroft windows is 80 years, twice that of the uPCV windows (40 years).

The Products Tested

The three Gowercroft products tested were:

  1. Hardwick Flush Casement Window in Red Grandis
  2. Richmond Flush Casement Window in Accoya®
  3. Accadia Flush Casement in Accoya®

The comparison products from other manufacturers were:

  1. Mumford and Wood Conservation Casement Window in Hardwood
  2. QKE EPPA window in uPVC
  3. Kawneer AA541/AA542 Aluminium window.

Where did the information come from?

Life cycle assessment data for Gowercroft products was calculated using the Building Research Establishment LINA tool. Data for the other windows was taken from published Environmental Product Declarations. In all cases a 1.23 x 1.48m window size was used for comparison. 

Results of the Sustainable Windows Study

Research graph

Gowercroft comparison with other timber window suppliers

Comparison of the Gowercroft timber windows to the alternative timber and other material products highlights the low manufacturing emissions in the Gowercroft case. This is due to the efficient manufacturing and equipment used at the Gowercroft site.

Another notable feature of the timber results is the negative emissions attributed to the raw materials in the Hardwick Red Grandis case, and the alternative timber window. Both these windows are hardwood products, and these negative emissions indicate that the carbon dioxide absorbed by the timber during growth outweighs the emissions generated during the raw material extraction. Although softwoods also absorb carbon dioxide during growth, due to their faster growing nature, the absorption is lower and hence some greenhouse gas emissions are seen from raw materials in Accoya wood cases. 

Comparison to Aluminium-framed windows

Across the cradle-to-gate assessment, the aluminium-framed window product has higher greenhouse gas emissions than all timber window products. Due to its light weight, the aluminium product has lower transport emissions than timber (though only pre-manufacture transport is included in the assessment for aluminium), but the complex and environmentally damaging process of bauxite extraction and refinement the aluminium product has very high greenhouse gas emissions in the raw material category. The manufacturing of the aluminium window from raw materials is also an energy-intensive process, and has significant emissions.

Comparison to uPVC-framed windows

In the uPVC case, the published information does not provide a breakdown of the relative emissions from each of A1, A2 and A3 categories, instead giving a single figure which includes the total of these processes. It is therefore not possible to identify the relative contribution of materials, transport and manufacturing. Since uPVC is a relatively light material, the transport element of this total is likely to be relatively small. No information on the material transport process is given in the published information, and it appears that this contribution has been assumed to be very small. It is difficult to ascertain the data sources used in the uPVC results, and some results appear to be based on aggregated information across manufacturers. The contribution of raw material production and manufacturing of uPVC windows are high, giving this product the highest A1-A3 total of all. uPVC also causes CO2 emissions since it is manufactured directly from fossil resources. This process depletes fossil resources through both the energy used and the raw materials.


This is the official conclusion from Dr Walkers sustainable windows report:

“All products have some impact on the environment, but materials and manufacturing methods have a significant impact on the level of these emissions. The three Gowercroft window products considered in this comparison have been found to have lower emissions than comparable products manufactured by other timber window manufacturers, and significantly lower emissions than those made from Aluminium and uPVC. This comparison has considered only the raw material and manufacture stages of the products, so a further comparison of the full life cycle emissions of Gowercroft products is recommended to fully understand the life cycle emissions and to consider the emissions reduction of window products when used to replace a low performance older window. End of life treatment is also excluded from this comparison but should be borne in mind, particularly in the uPVC case, considering the relatively short lifetime of this product.”

In short, Gowercroft windows are much, much kinder to the environment than the competition we tested.