![#](https://make-arch.imgix.net/https%3A%2F%2Fwww.makearchitects.com%2Fwp-content%2Fuploads%2F2021%2F08%2FLETI-hierarchy-for-embodied-carbon-reduction-modified-for-facades-by-FMDC-1-scaled.jpg?auto=format&crop=center&fit=crop&h=191&ixlib=php-1.2.1&w=210&s=fc21c26cbf5942a2c0cadd891dab4555 210w,https://make-arch.imgix.net/https%3A%2F%2Fwww.makearchitects.com%2Fwp-content%2Fuploads%2F2021%2F08%2FLETI-hierarchy-for-embodied-carbon-reduction-modified-for-facades-by-FMDC-1-scaled.jpg?auto=format&crop=center&fit=crop&h=383&ixlib=php-1.2.1&w=420&s=24f721489f68457e549b23ab177e981d 420w,https://make-arch.imgix.net/https%3A%2F%2Fwww.makearchitects.com%2Fwp-content%2Fuploads%2F2021%2F08%2FLETI-hierarchy-for-embodied-carbon-reduction-modified-for-facades-by-FMDC-1-scaled.jpg?auto=format&crop=center&fit=crop&h=700&ixlib=php-1.2.1&w=768&s=53c60bb885701869d591d579a75691d4 768w,https://make-arch.imgix.net/https%3A%2F%2Fwww.makearchitects.com%2Fwp-content%2Fuploads%2F2021%2F08%2FLETI-hierarchy-for-embodied-carbon-reduction-modified-for-facades-by-FMDC-1-scaled.jpg?auto=format&crop=center&fit=crop&h=934&ixlib=php-1.2.1&w=1024&s=89540a0a754d2fc176091f35c7c170d8 1024w,https://make-arch.imgix.net/https%3A%2F%2Fwww.makearchitects.com%2Fwp-content%2Fuploads%2F2021%2F08%2FLETI-hierarchy-for-embodied-carbon-reduction-modified-for-facades-by-FMDC-1-scaled.jpg?auto=format&crop=center&fit=crop&h=1276&ixlib=php-1.2.1&w=1400&s=0ab2d17c9d35163caf7eb62e9c3dc5b5 1400w,https://make-arch.imgix.net/https%3A%2F%2Fwww.makearchitects.com%2Fwp-content%2Fuploads%2F2021%2F08%2FLETI-hierarchy-for-embodied-carbon-reduction-modified-for-facades-by-FMDC-1-scaled.jpg?auto=format&crop=center&fit=crop&h=1459&ixlib=php-1.2.1&w=1600&s=846c3ec96f5da2e6d38fbc2e6f540772 1600w,https://make-arch.imgix.net/https%3A%2F%2Fwww.makearchitects.com%2Fwp-content%2Fuploads%2F2021%2F08%2FLETI-hierarchy-for-embodied-carbon-reduction-modified-for-facades-by-FMDC-1-scaled.jpg?auto=format&crop=center&fit=crop&h=1751&ixlib=php-1.2.1&w=1920&s=e41b4efdf20f23ed45eed35fad41c98d 1920w)
‘Build less’
Where possible, existing buildings and their facade systems should be refurbished rather than being replaced. Where facade systems cannot be re-furbished, their materials should be re-used or recycled for new facade elements, where this is viable. A new facade, installed on an existing building, may provide the opportunity to improve a building’s performance and reduce its operational energy, but this could also generate a significant amount of embodied carbon.
Stone taken from an existing facade could be re-used or re-purposed as the facing on new unitised facade panels. Insulating glass units could be reused or recycled into new architectural glass. Reusing existing materials not only helps to reduce a building’s UCE, it also helps preserve natural resources and biodiversity. Saint-Gobain Glass is currently the only glass manufacturer that operates a cullet return scheme in the UK, but others are expected to follow suit. A mechanism for taking advantage of the reduced UCE of recycled new glass remains to be developed.
‘Build light’
Building light involves engineering optimisation and more efficient facade design. This can lead to a reduction in the quantity of materials and a reduction in loads imposed on a primary frame. Optimising the architectural design of the facade by minimising or eradicating non-functional decorative elements and non-essential facing materials reduces the weight of a system, leading to a subsequent reduction in section and bracket sizes.
Ultra-High-Performance Concrete (‘UHPC’) panels may be used in place of traditional architectural precast concrete panels (Figure 2 below). While UHPC uses more cement than traditional precast, it is typically a third of the thickness of traditional precast, which results in a lower overall UCE. On top of this, the additional benefits of lighter UHPC panels are more efficient transportation to site and reduced loads on a primary frame. It should be noted that UHPC is best used with a facing material (e.g., brick, stone, terracotta), as the absence of aggregate in the mix means that the range of finishes is limited in comparison with traditional precast.
![#](https://make-arch.imgix.net/https%3A%2F%2Fwww.makearchitects.com%2Fwp-content%2Fuploads%2F2021%2F08%2FFigure-2-UHPC-panel-with-limestone-facing-Source_Hoffman-Facades-1.jpg?auto=format&crop=center&fit=crop&h=255&ixlib=php-1.2.1&w=210&s=ea79c421830d0ad34050e99be6123ec6 210w,https://make-arch.imgix.net/https%3A%2F%2Fwww.makearchitects.com%2Fwp-content%2Fuploads%2F2021%2F08%2FFigure-2-UHPC-panel-with-limestone-facing-Source_Hoffman-Facades-1.jpg?auto=format&crop=center&fit=crop&h=509&ixlib=php-1.2.1&w=420&s=cc53a8dc907743c66c25b5892fa61258 420w,https://make-arch.imgix.net/https%3A%2F%2Fwww.makearchitects.com%2Fwp-content%2Fuploads%2F2021%2F08%2FFigure-2-UHPC-panel-with-limestone-facing-Source_Hoffman-Facades-1.jpg?auto=format&crop=center&fit=crop&h=931&ixlib=php-1.2.1&w=768&s=316051705e76bb0b6bffa1763b9bbe6e 768w,https://make-arch.imgix.net/https%3A%2F%2Fwww.makearchitects.com%2Fwp-content%2Fuploads%2F2021%2F08%2FFigure-2-UHPC-panel-with-limestone-facing-Source_Hoffman-Facades-1.jpg?auto=format&crop=center&fit=crop&h=1241&ixlib=php-1.2.1&w=1024&s=73c943a7b85ca9593631b3bad439cfdd 1024w,https://make-arch.imgix.net/https%3A%2F%2Fwww.makearchitects.com%2Fwp-content%2Fuploads%2F2021%2F08%2FFigure-2-UHPC-panel-with-limestone-facing-Source_Hoffman-Facades-1.jpg?auto=format&crop=center&fit=crop&h=1697&ixlib=php-1.2.1&w=1400&s=85b19c9b4c282ace1007b29a1339f910 1400w,https://make-arch.imgix.net/https%3A%2F%2Fwww.makearchitects.com%2Fwp-content%2Fuploads%2F2021%2F08%2FFigure-2-UHPC-panel-with-limestone-facing-Source_Hoffman-Facades-1.jpg?auto=format&crop=center&fit=crop&h=1939&ixlib=php-1.2.1&w=1600&s=e2631c2a72cb91f1bf5088c9fa1522fc 1600w,https://make-arch.imgix.net/https%3A%2F%2Fwww.makearchitects.com%2Fwp-content%2Fuploads%2F2021%2F08%2FFigure-2-UHPC-panel-with-limestone-facing-Source_Hoffman-Facades-1.jpg?auto=format&crop=center&fit=crop&h=2327&ixlib=php-1.2.1&w=1920&s=d93a536f0f6e0a149683e17a88e0fb33 1920w)
‘Build wise’
To build wise means to select durable cladding materials and finishes, and to consider their service life and maintenance/replacement cycles. Generally, cladding materials require regular cleaning, but minimal maintenance.
Insulating glass units (‘IGUs’) and associated gaskets and seals are typically replaced after 25 years. Increasing the longevity of IGU seals, and finding a way to re-fill cavities with Argon, will be a key challenge for the architectural glass industry.
The aluminium framing of a curtain walling system has a predicted service life of 50-60 years, which is equivalent to the design life on most buildings currently. However, this does not apply to polyester powder coated (‘PPC’) finishes, applied to the framing, that have a predicted service life of 25 years. It could be beneficial to specify an anodised finish, despite its higher UCE in comparison in PPC, as a result of its longer service life.
A further way to build wise is to minimise waste by designing systems that can be manufactured off-site (e.g., unitised curtain walling, large panel systems). These systems can achieve high recycling rates for any redundant materials.
‘Build low carbon’
Building low carbon, by specifying renewable or recycled materials from responsible sources, is another key action. Specific measures can be taken to reduce the upfront carbon emissions of aluminium, glass and concrete.
Aluminium is one of the most durable and versatile materials used in facade construction, in the form of extruded profiles and sheeting for curtain wall, windows and doors. However, it has one of the highest UCE per kg of any material.
It is possible to use ‘low carbon aluminium’ by specifying either primary aluminium ingots produced with renewable energy, or aluminium ingots with a high post-consumer recycled aluminium content. Even though primary aluminium, produced from CO2 free energy, is widely available from several aluminium producers and is used by various façade companies, the high recycled content ingots are only available from Hydro and mostly for their in-house façade systems. An important distinction between pre-consumer and post-consumer aluminium scrap should be made; the former being aluminium that has never been in service (e.g., from fabrication off-cuts) and the latter being aluminium that had a useful life in the form of windows, etc., and has been subsequently dismantled and recycled. Unfortunately, there is not enough post-consumer aluminium scrap available for recycling today, or capacity to sort it efficiently, which means that it accounts for only approximately 20% of the current total aluminium supply in Europe (the percentage is even lower in the construction industry). However, according to the European Aluminium Association, there is potential to achieve close to 50% of the total demand with post-consumer aluminium by 2050.
![#](https://make-arch.imgix.net/https%3A%2F%2Fwww.makearchitects.com%2Fwp-content%2Fuploads%2F2021%2F08%2FFigure-3-European-aluminium-supply-2019-2030-and-2050-Source_CRU-2019-found-in-Circular-Aluminium-Action-Plan-by-European-Aluminium-1.jpg?auto=format&crop=center&fit=crop&h=125&ixlib=php-1.2.1&w=210&s=b0cb4754f30df511d441ccea965f3ca5 210w,https://make-arch.imgix.net/https%3A%2F%2Fwww.makearchitects.com%2Fwp-content%2Fuploads%2F2021%2F08%2FFigure-3-European-aluminium-supply-2019-2030-and-2050-Source_CRU-2019-found-in-Circular-Aluminium-Action-Plan-by-European-Aluminium-1.jpg?auto=format&crop=center&fit=crop&h=250&ixlib=php-1.2.1&w=420&s=b16e5ed7b9d10046eb8a672838ce9d7d 420w,https://make-arch.imgix.net/https%3A%2F%2Fwww.makearchitects.com%2Fwp-content%2Fuploads%2F2021%2F08%2FFigure-3-European-aluminium-supply-2019-2030-and-2050-Source_CRU-2019-found-in-Circular-Aluminium-Action-Plan-by-European-Aluminium-1.jpg?auto=format&crop=center&fit=crop&h=458&ixlib=php-1.2.1&w=768&s=fc1ea238f01d38c4718953659dd92abe 768w,https://make-arch.imgix.net/https%3A%2F%2Fwww.makearchitects.com%2Fwp-content%2Fuploads%2F2021%2F08%2FFigure-3-European-aluminium-supply-2019-2030-and-2050-Source_CRU-2019-found-in-Circular-Aluminium-Action-Plan-by-European-Aluminium-1.jpg?auto=format&crop=center&fit=crop&h=610&ixlib=php-1.2.1&w=1024&s=16159f8717ba25b8680dae8e5c433bb3 1024w,https://make-arch.imgix.net/https%3A%2F%2Fwww.makearchitects.com%2Fwp-content%2Fuploads%2F2021%2F08%2FFigure-3-European-aluminium-supply-2019-2030-and-2050-Source_CRU-2019-found-in-Circular-Aluminium-Action-Plan-by-European-Aluminium-1.jpg?auto=format&crop=center&fit=crop&h=835&ixlib=php-1.2.1&w=1400&s=f63a02e9d5eb1603a34d0df7e6ec4d7c 1400w,https://make-arch.imgix.net/https%3A%2F%2Fwww.makearchitects.com%2Fwp-content%2Fuploads%2F2021%2F08%2FFigure-3-European-aluminium-supply-2019-2030-and-2050-Source_CRU-2019-found-in-Circular-Aluminium-Action-Plan-by-European-Aluminium-1.jpg?auto=format&crop=center&fit=crop&h=954&ixlib=php-1.2.1&w=1600&s=24e660468c7c6c34c79bbdd527ce659d 1600w,https://make-arch.imgix.net/https%3A%2F%2Fwww.makearchitects.com%2Fwp-content%2Fuploads%2F2021%2F08%2FFigure-3-European-aluminium-supply-2019-2030-and-2050-Source_CRU-2019-found-in-Circular-Aluminium-Action-Plan-by-European-Aluminium-1.jpg?auto=format&crop=center&fit=crop&h=1145&ixlib=php-1.2.1&w=1920&s=bcae430fe2cc8a29d410c8f1a43e8aba 1920w)
Glass is a unique material in that it is 100% recyclable, it is resistant to chemicals and has special aesthetic properties. Even though cullet (i.e., recycled glass) lowers the UCE of new glass, insulating glass units are not commonly recycled into new architectural glass, but rather downcycled. Nevertheless, there are steps that can be taken to reduce the UCE of insulating glass units, which do not involve recycling of existing glass. Generally, mid or reduced iron glass has a lower embodied carbon than full low-iron glass as the former has a higher percentage of cullet. Annealed glass has a lower embodied carbon than heat-treated glass, but a single monolithic toughened glass pane has a lower embodied carbon than a laminated annealed glass pane. A low-carbon glazing approach is one where glass build-ups have been carefully optimised by considering their UCE along with the other performance factors.
![#](https://make-arch.imgix.net/https%3A%2F%2Fwww.makearchitects.com%2Fwp-content%2Fuploads%2F2021%2F08%2FFigure-4-Upfront-carbon-emissions-A1-A3-of-double-glazed-units-based-on-EPD-from-Saint-Gobain-Glass.jpg?auto=format&crop=center&fit=crop&h=148&ixlib=php-1.2.1&w=210&s=ed276697dcde1fd4f6dac1513ba3c560 210w,https://make-arch.imgix.net/https%3A%2F%2Fwww.makearchitects.com%2Fwp-content%2Fuploads%2F2021%2F08%2FFigure-4-Upfront-carbon-emissions-A1-A3-of-double-glazed-units-based-on-EPD-from-Saint-Gobain-Glass.jpg?auto=format&crop=center&fit=crop&h=297&ixlib=php-1.2.1&w=420&s=12d177c3b16991a1d4e2f6f584bcfc01 420w,https://make-arch.imgix.net/https%3A%2F%2Fwww.makearchitects.com%2Fwp-content%2Fuploads%2F2021%2F08%2FFigure-4-Upfront-carbon-emissions-A1-A3-of-double-glazed-units-based-on-EPD-from-Saint-Gobain-Glass.jpg?auto=format&crop=center&fit=crop&h=543&ixlib=php-1.2.1&w=768&s=ab12979c1a96797f970ffad51ed20523 768w,https://make-arch.imgix.net/https%3A%2F%2Fwww.makearchitects.com%2Fwp-content%2Fuploads%2F2021%2F08%2FFigure-4-Upfront-carbon-emissions-A1-A3-of-double-glazed-units-based-on-EPD-from-Saint-Gobain-Glass.jpg?auto=format&crop=center&fit=crop&h=724&ixlib=php-1.2.1&w=1024&s=0b0ee42e5803dda3a26c7a85963a3a63 1024w,https://make-arch.imgix.net/https%3A%2F%2Fwww.makearchitects.com%2Fwp-content%2Fuploads%2F2021%2F08%2FFigure-4-Upfront-carbon-emissions-A1-A3-of-double-glazed-units-based-on-EPD-from-Saint-Gobain-Glass.jpg?auto=format&crop=center&fit=crop&h=990&ixlib=php-1.2.1&w=1400&s=2a90f9d1a2d90c026d15642c8c40cadc 1400w,https://make-arch.imgix.net/https%3A%2F%2Fwww.makearchitects.com%2Fwp-content%2Fuploads%2F2021%2F08%2FFigure-4-Upfront-carbon-emissions-A1-A3-of-double-glazed-units-based-on-EPD-from-Saint-Gobain-Glass.jpg?auto=format&crop=center&fit=crop&h=1131&ixlib=php-1.2.1&w=1600&s=874b3b4ad83d3f8a182d11e3c4b8914a 1600w,https://make-arch.imgix.net/https%3A%2F%2Fwww.makearchitects.com%2Fwp-content%2Fuploads%2F2021%2F08%2FFigure-4-Upfront-carbon-emissions-A1-A3-of-double-glazed-units-based-on-EPD-from-Saint-Gobain-Glass.jpg?auto=format&crop=center&fit=crop&h=1358&ixlib=php-1.2.1&w=1920&s=f5f7bde1ede56606067b9cf9c27ac8f9 1920w)
Precast concrete is typically used as a panelised facade system in 150mm thickness either fair faced or with various facing materials, and is preferred because of its high-quality finish, off-site manufacture, and speed of erection. Surprisingly, it also has a low UCE per m2 of facade, when compared to an aluminium curtain walling system. Cement replacement can have the biggest impact in reducing its UCE, as approximately 60% of the total UCE of a precast concrete facade panel comes from cement production. Up to 50% of the Portland cement can be practically replaced by Ground Granulated Blast-furnace Slag (‘GGBS’), a by-product of the steel industry. This can lead to a reduction of approximately 25% in the overall UCE. Other advantages of GGBS cement are its lighter colour, smoother texture, and a reduction in the occurrence of efflorescence. However, GGBS cement cures more slowly than Portland cement, which slows down the production process and increases the cost of manufacture. In higher concentrations, it also has a distinct blue hue, which is not ideal for architectural fair-faced concrete finishes. Finally, as there is a shortage of GGBS in the UK currently (Source: BEIS Research Paper No. 19), it is important to take the source of the GGBS into account.
‘Build for the future’
Designing flexible and adaptable façades that can be easily maintained and upgraded is the key when thinking about the future. The most common way to upgrade an existing curtain walling or window system is to replace the insulating glass units at the end of their service life with higher performing ones, providing the framing system remains in good condition. Replacement is easier to achieve, and results in lower carbon emissions, if dry glazed gasket systems are used rather than structurally glazed ones.
Building for the future also requires focussing on design-for-disassembly and circular economy principles for the end of life of the facade. The appropriate design of mechanical connections, specifying IGUs that are easier to reuse and recycle, and keeping a detailed record of all materials employed in the construction, can aid their future re-use and recyclability. More specifically IGUs are easier to recycle if the following are avoided: ceramic frits and prints, body-tinted glass, and laminated glass panes with thick interlayers (currently only laminated glass panes with a 0.76mm thick PVB interlayer can be recycled).
‘Build collaboratively’
The final step, but possibly the most important one, is to build collaboratively, by sharing knowledge between parties. This is crucial because the process of measuring, verifying and disclosing whole life carbon values is still in its infancy and is continuously evolving. Fruitful interdisciplinary collaboration and open book data are essential to build net-zero carbon buildings, and we all must help towards this goal.
- Figure 1 – LETI hierarchy for embodied carbon reduction, modified for facades by FMDC
- Figure 2 – UHPC panel with limestone facing (Source: Hofmann Facades)
- Figure 3 – European aluminium supply – 2019, 2030 and 2050 (Source: CRU, 2019, found in Circular Aluminium Action Plan by European Aluminium)
- Figure 4 – Upfront carbon emissions (A1-A3) of double-glazed units based on EPD from Saint-Gobain Glass