![#](https://make-arch.imgix.net/https%3A%2F%2Fwww.makearchitects.com%2Fwp-content%2Fuploads%2F2021%2F09%2F2_facade-systems.jpg?auto=format&crop=center&fit=crop&h=118&ixlib=php-1.2.1&w=210&s=301638b82c68c8a87f7886dc69e7c819 210w,https://make-arch.imgix.net/https%3A%2F%2Fwww.makearchitects.com%2Fwp-content%2Fuploads%2F2021%2F09%2F2_facade-systems.jpg?auto=format&crop=center&fit=crop&h=237&ixlib=php-1.2.1&w=420&s=9ba671d80141ff7c4c67535c1aeca0e0 420w,https://make-arch.imgix.net/https%3A%2F%2Fwww.makearchitects.com%2Fwp-content%2Fuploads%2F2021%2F09%2F2_facade-systems.jpg?auto=format&crop=center&fit=crop&h=433&ixlib=php-1.2.1&w=768&s=48f502fef62817bbea8b6f8b3a48c74f 768w,https://make-arch.imgix.net/https%3A%2F%2Fwww.makearchitects.com%2Fwp-content%2Fuploads%2F2021%2F09%2F2_facade-systems.jpg?auto=format&crop=center&fit=crop&h=577&ixlib=php-1.2.1&w=1024&s=7a904cbbd56baa91f2d77450d04a9eae 1024w,https://make-arch.imgix.net/https%3A%2F%2Fwww.makearchitects.com%2Fwp-content%2Fuploads%2F2021%2F09%2F2_facade-systems.jpg?auto=format&crop=center&fit=crop&h=789&ixlib=php-1.2.1&w=1400&s=d52534186d9694989818f864f90d1e5e 1400w,https://make-arch.imgix.net/https%3A%2F%2Fwww.makearchitects.com%2Fwp-content%2Fuploads%2F2021%2F09%2F2_facade-systems.jpg?auto=format&crop=center&fit=crop&h=901&ixlib=php-1.2.1&w=1600&s=6d9fd1fae88259eec889307c17e8a334 1600w,https://make-arch.imgix.net/https%3A%2F%2Fwww.makearchitects.com%2Fwp-content%2Fuploads%2F2021%2F09%2F2_facade-systems.jpg?auto=format&crop=center&fit=crop&h=1082&ixlib=php-1.2.1&w=1920&s=dbe34304e877534a2a873e498520c10b 1920w)
The calculations above are for just the solid part of the facade so we need a bay study to see the effect of adding in windows. Our previous study looked at a bay of unitized curtain walling, so let’s run some numbers on the precast system this time. With 40% glazing, double-laminated double-glazing in a fixed aluminium frame, the bay averages 173 kgCO2e per m2 of facade area.
![#](https://make-arch.imgix.net/https%3A%2F%2Fwww.makearchitects.com%2Fwp-content%2Fuploads%2F2021%2F09%2F3_precast_bay_study-page.jpg?auto=format&crop=center&fit=crop&h=118&ixlib=php-1.2.1&w=210&s=8e50ddfbd3f82f858a5dfda7f577e6c8 210w,https://make-arch.imgix.net/https%3A%2F%2Fwww.makearchitects.com%2Fwp-content%2Fuploads%2F2021%2F09%2F3_precast_bay_study-page.jpg?auto=format&crop=center&fit=crop&h=237&ixlib=php-1.2.1&w=420&s=a6841743c36d0ff74807b185fee74e45 420w,https://make-arch.imgix.net/https%3A%2F%2Fwww.makearchitects.com%2Fwp-content%2Fuploads%2F2021%2F09%2F3_precast_bay_study-page.jpg?auto=format&crop=center&fit=crop&h=433&ixlib=php-1.2.1&w=768&s=6d68eb4f4f44ce75060a435401b0aa37 768w,https://make-arch.imgix.net/https%3A%2F%2Fwww.makearchitects.com%2Fwp-content%2Fuploads%2F2021%2F09%2F3_precast_bay_study-page.jpg?auto=format&crop=center&fit=crop&h=577&ixlib=php-1.2.1&w=1024&s=bb81b11fa3561724ccaa0f1c925f2f55 1024w,https://make-arch.imgix.net/https%3A%2F%2Fwww.makearchitects.com%2Fwp-content%2Fuploads%2F2021%2F09%2F3_precast_bay_study-page.jpg?auto=format&crop=center&fit=crop&h=789&ixlib=php-1.2.1&w=1400&s=9311c24db9adf1abeb70031e84dd4e4a 1400w,https://make-arch.imgix.net/https%3A%2F%2Fwww.makearchitects.com%2Fwp-content%2Fuploads%2F2021%2F09%2F3_precast_bay_study-page.jpg?auto=format&crop=center&fit=crop&h=901&ixlib=php-1.2.1&w=1600&s=3b55390a8ef5dc7edb076740268bbb7b 1600w,https://make-arch.imgix.net/https%3A%2F%2Fwww.makearchitects.com%2Fwp-content%2Fuploads%2F2021%2F09%2F3_precast_bay_study-page.jpg?auto=format&crop=center&fit=crop&h=1082&ixlib=php-1.2.1&w=1920&s=c2984a876cb11657c867e227dbe3cb4b 1920w)
This is still counting kgCO2e per square metre of facade, whereas the standard measure of embodied carbon is kgCO2e per square metre of floor area, the gross internal area (GIA). To convert this, we need to know the size and shape of the building as the efficiency of the form and its wall to floor ratio determines how thinly we can spread the carbon footprint of our facade. Efficiency of form is key, as discussed in our first article. The examples below show two large office floorplates of the same area but with very different wall to floor ratios. Our precast facade on a compact, deep plan floorplate is 55kgCO2e/m2 GIA whereas exactly the same facade on an elongated, narrow plan floorplate is 85 kgCO2e/m2 GIA. No material or design changes in the facade will be enough to compensate for the difference in the building shape. It’s why embodied carbon thinking has to start at the very first sketches for a project and be part of the conversation – with clients, planners and the rest of the design team – from the very start.
![#](https://make-arch.imgix.net/https%3A%2F%2Fwww.makearchitects.com%2Fwp-content%2Fuploads%2F2021%2F09%2F4_walltofloorratio-page.jpg?auto=format&crop=center&fit=crop&h=118&ixlib=php-1.2.1&w=210&s=96f495258767324a71b7813b9d228ca7 210w,https://make-arch.imgix.net/https%3A%2F%2Fwww.makearchitects.com%2Fwp-content%2Fuploads%2F2021%2F09%2F4_walltofloorratio-page.jpg?auto=format&crop=center&fit=crop&h=237&ixlib=php-1.2.1&w=420&s=7069ce783c7f865729f01b2f1bfa070a 420w,https://make-arch.imgix.net/https%3A%2F%2Fwww.makearchitects.com%2Fwp-content%2Fuploads%2F2021%2F09%2F4_walltofloorratio-page.jpg?auto=format&crop=center&fit=crop&h=433&ixlib=php-1.2.1&w=768&s=690060bcc702a3ce1b28d35caa31c6dd 768w,https://make-arch.imgix.net/https%3A%2F%2Fwww.makearchitects.com%2Fwp-content%2Fuploads%2F2021%2F09%2F4_walltofloorratio-page.jpg?auto=format&crop=center&fit=crop&h=577&ixlib=php-1.2.1&w=1024&s=29371b7d673b68016866291d7707633b 1024w,https://make-arch.imgix.net/https%3A%2F%2Fwww.makearchitects.com%2Fwp-content%2Fuploads%2F2021%2F09%2F4_walltofloorratio-page.jpg?auto=format&crop=center&fit=crop&h=789&ixlib=php-1.2.1&w=1400&s=12f1d691889c59161b005f2e8da7f6fc 1400w,https://make-arch.imgix.net/https%3A%2F%2Fwww.makearchitects.com%2Fwp-content%2Fuploads%2F2021%2F09%2F4_walltofloorratio-page.jpg?auto=format&crop=center&fit=crop&h=901&ixlib=php-1.2.1&w=1600&s=300470f0411f2c0468a992793ec1c5da 1600w,https://make-arch.imgix.net/https%3A%2F%2Fwww.makearchitects.com%2Fwp-content%2Fuploads%2F2021%2F09%2F4_walltofloorratio-page.jpg?auto=format&crop=center&fit=crop&h=1082&ixlib=php-1.2.1&w=1920&s=54b7fd3541382ce151c7028453b63e31 1920w)
Now that we have an embodied carbon number relative to floor area, we can benchmark it. The most common benchmark is the LETI Embodied Carbon Target Alignment, with ratings from A++ to G.
![#](https://make-arch.imgix.net/https%3A%2F%2Fwww.makearchitects.com%2Fwp-content%2Fuploads%2F2021%2F09%2F5_LETI_target_alignment_table.jpg?auto=format&crop=center&fit=crop&h=93&ixlib=php-1.2.1&w=210&s=27cdaddf73676e01b993a398b896f5ac 210w,https://make-arch.imgix.net/https%3A%2F%2Fwww.makearchitects.com%2Fwp-content%2Fuploads%2F2021%2F09%2F5_LETI_target_alignment_table.jpg?auto=format&crop=center&fit=crop&h=186&ixlib=php-1.2.1&w=420&s=d76eaff66edd8791319d7ea41d54614b 420w,https://make-arch.imgix.net/https%3A%2F%2Fwww.makearchitects.com%2Fwp-content%2Fuploads%2F2021%2F09%2F5_LETI_target_alignment_table.jpg?auto=format&crop=center&fit=crop&h=339&ixlib=php-1.2.1&w=768&s=fba12bf1240ae95cbc8b6adb3d8b31f6 768w,https://make-arch.imgix.net/https%3A%2F%2Fwww.makearchitects.com%2Fwp-content%2Fuploads%2F2021%2F09%2F5_LETI_target_alignment_table.jpg?auto=format&crop=center&fit=crop&h=452&ixlib=php-1.2.1&w=1024&s=c4df93fb27e8dc6010959c376c5b619f 1024w,https://make-arch.imgix.net/https%3A%2F%2Fwww.makearchitects.com%2Fwp-content%2Fuploads%2F2021%2F09%2F5_LETI_target_alignment_table.jpg?auto=format&crop=center&fit=crop&h=619&ixlib=php-1.2.1&w=1400&s=f9ffb59aa2a0078c3e5c26b3eacb941c 1400w,https://make-arch.imgix.net/https%3A%2F%2Fwww.makearchitects.com%2Fwp-content%2Fuploads%2F2021%2F09%2F5_LETI_target_alignment_table.jpg?auto=format&crop=center&fit=crop&h=707&ixlib=php-1.2.1&w=1600&s=44a9e458eb6ee063c3ee3a887ff2ce0a 1600w,https://make-arch.imgix.net/https%3A%2F%2Fwww.makearchitects.com%2Fwp-content%2Fuploads%2F2021%2F09%2F5_LETI_target_alignment_table.jpg?auto=format&crop=center&fit=crop&h=848&ixlib=php-1.2.1&w=1920&s=d019257b34b6ab9896e150b31053122d 1920w)
The LETI Embodied Carbon Primer has an indicative breakdown of the embodied carbon of different parts of the building across several building types; acknowledging that an office building has more mechanical and electrical services than a residential building, for example, and that a residential building with all its kitchens and bathrooms has a greater proportion of interior fit-out material than an office. We can use these typical benchmarks to break down the targets and look at the facade specifically.
![#](https://make-arch.imgix.net/https%3A%2F%2Fwww.makearchitects.com%2Fwp-content%2Fuploads%2F2021%2F09%2F6_LETI_Targets.jpg?auto=format&crop=center&fit=crop&h=118&ixlib=php-1.2.1&w=210&s=b679a0b7eb701296974322e58447989d 210w,https://make-arch.imgix.net/https%3A%2F%2Fwww.makearchitects.com%2Fwp-content%2Fuploads%2F2021%2F09%2F6_LETI_Targets.jpg?auto=format&crop=center&fit=crop&h=237&ixlib=php-1.2.1&w=420&s=3594eb6e3e24a42d714c4bb4598cdbb6 420w,https://make-arch.imgix.net/https%3A%2F%2Fwww.makearchitects.com%2Fwp-content%2Fuploads%2F2021%2F09%2F6_LETI_Targets.jpg?auto=format&crop=center&fit=crop&h=433&ixlib=php-1.2.1&w=768&s=ea82a39fa468ca9b9f759a6b1c6d7157 768w,https://make-arch.imgix.net/https%3A%2F%2Fwww.makearchitects.com%2Fwp-content%2Fuploads%2F2021%2F09%2F6_LETI_Targets.jpg?auto=format&crop=center&fit=crop&h=577&ixlib=php-1.2.1&w=1024&s=f6fb87455d3080b5478327a8781d2fa6 1024w,https://make-arch.imgix.net/https%3A%2F%2Fwww.makearchitects.com%2Fwp-content%2Fuploads%2F2021%2F09%2F6_LETI_Targets.jpg?auto=format&crop=center&fit=crop&h=789&ixlib=php-1.2.1&w=1400&s=265334780ee78073c45e813a66730d66 1400w,https://make-arch.imgix.net/https%3A%2F%2Fwww.makearchitects.com%2Fwp-content%2Fuploads%2F2021%2F09%2F6_LETI_Targets.jpg?auto=format&crop=center&fit=crop&h=901&ixlib=php-1.2.1&w=1600&s=29b8ae4afe5e5a244c440fae786334e4 1600w,https://make-arch.imgix.net/https%3A%2F%2Fwww.makearchitects.com%2Fwp-content%2Fuploads%2F2021%2F09%2F6_LETI_Targets.jpg?auto=format&crop=center&fit=crop&h=1082&ixlib=php-1.2.1&w=1920&s=76d1206421db35e62da9bd025f88a374 1920w)
Again, building shape is key; the same office facade achieves a Band A or a Band C rating depending on wall to floor ratio. Of course, deep plan and shallow plan offices are lit and serviced differently, but in pure embodied carbon terms, efficiency is all. Size also helps; the smaller residential floor plates have a much harder job – and tougher targets.
![#](https://make-arch.imgix.net/https%3A%2F%2Fwww.makearchitects.com%2Fwp-content%2Fuploads%2F2021%2F09%2F7_facade-targets.jpg?auto=format&crop=center&fit=crop&h=118&ixlib=php-1.2.1&w=210&s=cea273001e6beb333d3d9d153f88fd05 210w,https://make-arch.imgix.net/https%3A%2F%2Fwww.makearchitects.com%2Fwp-content%2Fuploads%2F2021%2F09%2F7_facade-targets.jpg?auto=format&crop=center&fit=crop&h=237&ixlib=php-1.2.1&w=420&s=f215911e0d70f733dc2fbdd689561bf4 420w,https://make-arch.imgix.net/https%3A%2F%2Fwww.makearchitects.com%2Fwp-content%2Fuploads%2F2021%2F09%2F7_facade-targets.jpg?auto=format&crop=center&fit=crop&h=433&ixlib=php-1.2.1&w=768&s=3ac66e7714f23dd7bbc3a9e2c7d37c30 768w,https://make-arch.imgix.net/https%3A%2F%2Fwww.makearchitects.com%2Fwp-content%2Fuploads%2F2021%2F09%2F7_facade-targets.jpg?auto=format&crop=center&fit=crop&h=577&ixlib=php-1.2.1&w=1024&s=7d8de4fd30b28b2060b752cb64a3ead0 1024w,https://make-arch.imgix.net/https%3A%2F%2Fwww.makearchitects.com%2Fwp-content%2Fuploads%2F2021%2F09%2F7_facade-targets.jpg?auto=format&crop=center&fit=crop&h=789&ixlib=php-1.2.1&w=1400&s=1ad90c076080e9722ce065514432b80c 1400w,https://make-arch.imgix.net/https%3A%2F%2Fwww.makearchitects.com%2Fwp-content%2Fuploads%2F2021%2F09%2F7_facade-targets.jpg?auto=format&crop=center&fit=crop&h=901&ixlib=php-1.2.1&w=1600&s=0856930e24953bfeccd55662c99c5ae5 1600w,https://make-arch.imgix.net/https%3A%2F%2Fwww.makearchitects.com%2Fwp-content%2Fuploads%2F2021%2F09%2F7_facade-targets.jpg?auto=format&crop=center&fit=crop&h=1082&ixlib=php-1.2.1&w=1920&s=2f0972c45f281cd4d1e9fbf94f2b7342 1920w)
We can use the unitized bay studies from our earlier article to understand the impact of using a different facade system. A stone rainscreen on a unitized facade is much higher embodied carbon than stone-faced precast, so only if the lighter loads of the unitized system led to significant savings in the primary structure would its use be justified in carbon terms. The flush, low-carbon sourced aluminium option (of which there is limited supply) beats the stone-faced precast concrete system. However, rather than a flush aluminium and glass facade, architects usually dress our curtain walls with ribs or textures or rainscreens or fins; perhaps increasing solar shading but always increasing embodied carbon.
![#](https://make-arch.imgix.net/https%3A%2F%2Fwww.makearchitects.com%2Fwp-content%2Fuploads%2F2021%2F09%2F8_unitized-options.jpg?auto=format&crop=center&fit=crop&h=118&ixlib=php-1.2.1&w=210&s=5bafd52d9cf66bb10d624b588e5796fc 210w,https://make-arch.imgix.net/https%3A%2F%2Fwww.makearchitects.com%2Fwp-content%2Fuploads%2F2021%2F09%2F8_unitized-options.jpg?auto=format&crop=center&fit=crop&h=237&ixlib=php-1.2.1&w=420&s=d60b3cbcaa196fa98155e5382dce0e6e 420w,https://make-arch.imgix.net/https%3A%2F%2Fwww.makearchitects.com%2Fwp-content%2Fuploads%2F2021%2F09%2F8_unitized-options.jpg?auto=format&crop=center&fit=crop&h=433&ixlib=php-1.2.1&w=768&s=c106f0299d5491af1f9b3848771119ff 768w,https://make-arch.imgix.net/https%3A%2F%2Fwww.makearchitects.com%2Fwp-content%2Fuploads%2F2021%2F09%2F8_unitized-options.jpg?auto=format&crop=center&fit=crop&h=577&ixlib=php-1.2.1&w=1024&s=9eb9404f7fc31648d97101bf5620f4a7 1024w,https://make-arch.imgix.net/https%3A%2F%2Fwww.makearchitects.com%2Fwp-content%2Fuploads%2F2021%2F09%2F8_unitized-options.jpg?auto=format&crop=center&fit=crop&h=789&ixlib=php-1.2.1&w=1400&s=dce24ed4563532ebc53dabcdecfd85d8 1400w,https://make-arch.imgix.net/https%3A%2F%2Fwww.makearchitects.com%2Fwp-content%2Fuploads%2F2021%2F09%2F8_unitized-options.jpg?auto=format&crop=center&fit=crop&h=901&ixlib=php-1.2.1&w=1600&s=caccec70600af64fc2fb53ca721bee90 1600w,https://make-arch.imgix.net/https%3A%2F%2Fwww.makearchitects.com%2Fwp-content%2Fuploads%2F2021%2F09%2F8_unitized-options.jpg?auto=format&crop=center&fit=crop&h=1082&ixlib=php-1.2.1&w=1920&s=8504f75b50a3c9e4477ac3b4bf7ad9d0 1920w)
So how low can we go? There are lots of ways to reduce the embodied carbon of a precast facade system and some examples are shown below with their relative carbon impact (based on this theoretical study – specific project factors will change the balance). It’s important to understand and compare the carbon benefit of each move to spend our design time and project budget in the most effective way.
![#](https://make-arch.imgix.net/https%3A%2F%2Fwww.makearchitects.com%2Fwp-content%2Fuploads%2F2021%2F09%2F9_precast_options.jpg?auto=format&crop=center&fit=crop&h=118&ixlib=php-1.2.1&w=210&s=27a82a57721be492412d1ad068c7651e 210w,https://make-arch.imgix.net/https%3A%2F%2Fwww.makearchitects.com%2Fwp-content%2Fuploads%2F2021%2F09%2F9_precast_options.jpg?auto=format&crop=center&fit=crop&h=237&ixlib=php-1.2.1&w=420&s=ecb31ccb19d3bd0f59f946fff20f519a 420w,https://make-arch.imgix.net/https%3A%2F%2Fwww.makearchitects.com%2Fwp-content%2Fuploads%2F2021%2F09%2F9_precast_options.jpg?auto=format&crop=center&fit=crop&h=433&ixlib=php-1.2.1&w=768&s=02fd0acb3a5dc453257388613f8dcd3a 768w,https://make-arch.imgix.net/https%3A%2F%2Fwww.makearchitects.com%2Fwp-content%2Fuploads%2F2021%2F09%2F9_precast_options.jpg?auto=format&crop=center&fit=crop&h=577&ixlib=php-1.2.1&w=1024&s=dc1b78fbf52bc9f14bb1bd5b8e64f7ad 1024w,https://make-arch.imgix.net/https%3A%2F%2Fwww.makearchitects.com%2Fwp-content%2Fuploads%2F2021%2F09%2F9_precast_options.jpg?auto=format&crop=center&fit=crop&h=789&ixlib=php-1.2.1&w=1400&s=e00159e091ee8f56fdbadf8fee9ea448 1400w,https://make-arch.imgix.net/https%3A%2F%2Fwww.makearchitects.com%2Fwp-content%2Fuploads%2F2021%2F09%2F9_precast_options.jpg?auto=format&crop=center&fit=crop&h=901&ixlib=php-1.2.1&w=1600&s=3efce2938f2382032541005ec208a8e2 1600w,https://make-arch.imgix.net/https%3A%2F%2Fwww.makearchitects.com%2Fwp-content%2Fuploads%2F2021%2F09%2F9_precast_options.jpg?auto=format&crop=center&fit=crop&h=1082&ixlib=php-1.2.1&w=1920&s=037d66e90da2f08ed126cf525e138cb1 1920w)
Quantifying potential changes in the facade means they can be weighed against other parts of the build. Adding opening windows will increase embodied carbon in the facade but how much could it save in the ventilation and cooling systems? What operational energy would it save and what would the pay-back period be?
The changes to the precast facade identified here total in the order of 20kgCO2e/m2 GIA. To put that in perspective, a metal suspended ceiling system is typically 20kgCO2e/m2 and covers perhaps 75% of the building floor area. Omitting ceilings, exposing services, and using felt or plasterboard baffles for acoustics can save significant carbon. Similarly, a metal-encapsulated raised access floor system is 50kgCO2e/m2 whereas using refurbished pans with new pedestals would be 12kgCO2e/m2, saving 38kgCO2e/m2 across 75% of the GIA. Floorslabs, raised floors and ceilings are blanketed across every square meter, whereas the facade is just around the perimeter and its impact is ‘diluted’ by the wall to floor ratio. Provided that an inherently lower carbon facade system has been chosen and the wall to floor ratio is efficient, then changes in the detailed specification of the facade may not deliver such cost-effective carbon savings as the potential for other parts of the building.
So efficient facades on efficient buildings should be able to meet the LETI targets – but is that good enough? Or in the words of the seminal book ‘Cradle to Cradle’ are we just being less bad? We are in the midst of a climate emergency and our planetary systems are out of balance: every kg of greenhouse gas emitted is increasing climate instability in the near future. To quote Doughnut Economics, how can our buildings be ‘regenerative by design’: not just be good but do good? Regenerative facades would sequester carbon by using biogenic materials; they would generate power; host biodiversity; filter rainwater; soak up noise and air pollution and cool the city; they would be made from components which can be reused, reconfigured or composted at the end of their life, and they would support community wellbeing and joy. And here we stray beyond the topic of embodied carbon to think holistically about the best that our buildings can be. Only by working together with the widest possible team, by listening and sharing, can we move from ‘less bad’ to ‘doing good’.