The kg/m2 and kWh/m2 (and embodied energy) 2/2

It is remarkable that the kg/m2 approach for buildings , as described in the previous article, is nearly completely absent. That is, nowadays. More then 100 years ago it was regularly used a a criterion in architectural competitions, the lower the better. [1] And famous is Buckminster Fuller, who used to ask colleague’s: How much does your building weigh…? He mainly innovated using the motto: ‘Less is more’. [2] Recently the issue has been picked up at MIT in the USA again, inspired by Catherine De Wolf [3] She started a extensive study into material quantities of buildings, documented many projects, which she coupled to CO2 emissions. I can recommend this study. In is a table in which she compares skyscrapers or high rises, and it turns out that the idea that my calculation for the Taipei 101 was too low, is right: in a more detailed analyses she comes to 2500 kg/m2 ( for only structural construction, not including finishes, facade panels etc) . Its an interesting table that shows that height creates more kg/m2, but also that there are enormous differences between towers: Again a question of architects /engineers not mastering their profession? The tower by Foster, the Gherkin, but officially the ‘ 30 St Mary Axe’ , is however incredibly low, There must be some parts missing in the calculation since it seems impossible to create a building with so little weight, let alone a high rise. To get an average I would leave out the highest and the lowest from the list.

Its a good moment to point out that it makes a lot of difference how the m2’s are calculated. In my calculations, I only take the useful floor area, or also called the rentable area. That excludes garages, balconies, staircases, corridors etc. In The Agrodome house ( see previous article), there was a lot on maneuvering space, ‘non-rentable area’, due to the fact it was a small and deep lay out. Which affected the result as well, since for weight all material is included, also for the corridors, balconies etc.

The data by MIT have been placed in a database and is free accessible, and which well be extended I presume. [4] The tower graph also shows that within a material category there can also be big differences. But hey, less is better, even within a more impact-rich material category. But again, these are basic data only structural elements. Mind that with organic or biobased buildings parts are usually integrated . Like with CLT , cross laminated timber, all walls and floors contribute to the structural performance, even sometimes facades.

After having calculated a kg/m2 indicator , a more detailed calculation could be executed, when we move from quantity to quality evaluation. Which will show that a few more improvements re possible. In principle, less material creates less impact, in embodied energy or CO2 emissions. And also when moving from non-biobased to biobased, , embodied energy and CO2 emissions generally will decrease. [5]

But there are some exceptions to which a good designer or engineer must be conceived. And we find these in the extremes of material use. For example, when a biobased building is made of one of the lowest impact materials possible: raw clay, or adobe (and mind that some 2 billion people still live in clay based houses,) , the weight of course increases. That is, the kg/m2, but not the impact!

Another extreme is when steel is replaced with aluminium, which in some cases leads to lower weight, but aluminium is a lot worse in impact, for buildings its the material with the most extreme impact, especially in embodied energy and CO2 emissions, so thats a bad deal. [6] Always carry out a ‘aluminium check’, and if there is a alternative, even if its a bit heavier, it should be used.

Another extreme , but now in the details, is that between bamboo and wood: Both biobased, and in principle bamboo would score better due to its high strength and higher yield per hectare grown, up to a factor 3. But the detail is here the glues that are used for bamboo. So far that is , with high strength engineered bamboo, phenol-formaldehyde, which kills the advantage (compared to wood). A better glue is possible, but for cost reasons not yet developed by industry. [6]

So far for the material versus material comparisons. But although we treat the evaluations separately between energy and materials, there is nevertheless another direct relation between energy and materials use, in case of products that require operational energy, like buildings. Striving for a very low operational energy, the kWh / m2 norm, can lead to a much higher kg / m2 value, and vice versa. Here also its in the extremes. Lower kWh/m2 values require materials investments, raising kg/m2 and indirectly embodied energy, which can also be expressed in kWh/m2. It then comes down to evaluating the combination of the two, so called life cycle energy approaches. * However, soon this might become superfluous, since we all want (net) 0-energy buildings to be the norm. In that case, the building still requires operational energy, but coming from renewables. And renewable energy has no impact ( wind , sun air) , the impact has been moved to the materials to reduce and produce the operational renewable energy. The whole building, including operational energy becomes a mass evaluation: construction plus insulation plus solar panels and everything else, like pipes and pumps that is needed to operate the building. Extreme (energy) reduction in those cases might not always be the best solution. [7] . To avoid a rebound effect in materials for a ZEB, its better to reduce the heated area, requiring less insulation material, less PV panels, reducing the kg/m2 …. ( In the Netherlands we only have a few real cold days in winter, its a lot of overkill to prepare a whole house as if it was winter all year) .

But nevertheless: the kg/m2 approach is a good proxy in the initial design phase, to have some clues about the level of impact , In the more extreme cases its always good to to a embodied or life cycle energy calculation to detail things .

Avoiding material at all, is of course the best strategy, as avoiding energy use is already for decades the best energy strategy!

* Research in Embodied energy:

if you are interested in more background on embodied energy, see the reports of the work in the IEA EBC annex 57 workgroup, with many case studies, and the papers published . And you ca follow the just started work in annex 72, lifecycle energy and environmental impacts.

http://www.iea-ebc.org/projects/project?AnnexID=57

http://annex72.iea-ebc.org/

book and some recent papers analyzing buildings embodied energy:

https://www.sciencedirect.com/science/article/pii/S0378778816319132

https://www.springer.com/us/book/9783319727950

https://www.sciencedirect.com/science/article/pii/S0378778817321576

https://www.sciencedirect.com/science/article/pii/S0378778817325720

more papers from Annex 57 at: http://www.annex57.org/?page_id=239

[1] https://www.slideshare.net/btolkachev/tower-for-london

[2] https://www.moma.org/collection/works/804

BF: “do more with less.”:

https://shedsistence.com/2014/11/13/how-much-does-your-house-weight/