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Elements of A Circular Built Environment - Beyond Net-Zero Targets

We chat with Paula Huerta, sustainable net-zero architecture expert, who shares with us her thoughts on what we need to do to create a built environment that is low-impact, fully circular, energy and resource-efficient, starting from the construction process all the way to use and even post-use by designing for disassembly.

A lot of buildings that are gonna be around in 2050 in Asia are yet to be built - what should we do to ensure minimal environmental impact for these projects?

Most of the focus right now is going into building performance. There are two types of net-zero targets for buildings - net-zero 2030, which means all the new buildings will be net-zero and net-zero 2050, which refers to even all existing buildings becoming net-zero. But these targets only relate to the performance of the building - all the water, energy and electricity usage. It does not reflect the consumption of resources through the construction process of such buildings. which has a huge environmental impact. A lot of current infrastructure has already been built - so for new buildings, it’s very important to do it right from the start. We need to go beyond building performance and start looking at how we can improve building design and construction methods to reduce the impact of the overall process.


If they are built using conventional methods, we will have to mine a lot of iron, steel, concrete and cement. What are some alternative building methods?


The big elephant in the room in construction is always concrete and steel. Concrete comes from limestone which you need to mine, yes, then the limestone needs to be produced into cement, and just cement production alone accounts for 8% of global GHG emissions. One kilo of Cement = 1 kg of CO2 to the atmosphere, before it even reaches the construction site.


Asia, in particular China during the urbanisation process, in one decade used more concrete than all the concrete the US has ever used. This shows just how much Asia’s footprint is through concrete usage. Concrete is very inefficient. Steel, believe or not, is 99% recycled, which is great, because the process of making new steel through iron is extremely polluting. Fortunately, steel can be made for disassembly, which is almost impossible for concrete. If we use only steel, it would be quite easy to dismantle and reuse again. Concrete uses sands and pebbles too, which comes from beaches, which also has several environmental impacts. What we need to do is get rid of the concrete, which uses cement and sand, and focus on more mechanic building styles or “lego” style - things that you can assemble, disassemble and reuse.


When you look at Singapore, there are building facades made of aluminium. But for aluminium to be a facade it needs to be new and not recycled, because of structural strength requirements which recycled alumnium does not fare well in. In general, I think we need to focus on exploring new materials - wood, and also bamboo. In terms of cities and skyscrapers, there is not much we can use yet. We are still using the same construction methods they used in the 50s to build New York and Chicago. We have not improved much at all, and continue to ignore the externalities that these materials bring.


The construction sector accounts for a huge impact on the environment, not only greenhouse gas emissions through the huge machinery and transportation that are used, but also other environmental impacts related to noise pollution, water pollution, chemical hazards, landscape depression, solid waste and dust. I think everyone is able to say they have been near a construction site and they felt disturbed. The disturbance from construction is enormous. Net-zero does not consider the impacts from the construction sector and that’s a failure. Some sources have stated that construction alone contributes to 50% of climate change, 40% of global energy and 50% of landfill waste.


How can we make the built environment circular or (Net) Zero Carbon and Zero Waste?


Since net-zero only focuses on the building performance, it means we only consider the usage of resources in the completed building and forget about all the impacts from construction we just talked about. Everything that has to do with the built environment has 3 elements -


  1. Design Designers need to know how to design better. That includes engineering methods, new technologies, smart buildings, all of that. We need to improve the way we design buildings so their performance is better and the environmental impact is lesser for construction as well. Even though the construction process does not last as long as a building, it does have huge impacts.

  2. Energy Usage In considering energy usage, there are two elements - 1. how the building has been designed and 2. how efficient the machines placed in the building are. Smart buildings are really good because they can ensure that no matter what the users do, you can implement strategies that help to improve performance. For example, the typical key that hotel rooms use - when you leave, and take out the key, all the electricity and aircon in the room turns off. This helps to ensure that even if clients forget to turn off the aircon and lights, they will be turned off automatically to save energy when they leave.


I think the future of a circular built environment will be a combination of design and a lot of technology and innovation in construction, materials and definitely a lot of digitalization of use through smart buildings.


What are some new innovations in building materials? Can we create secondary markets for building material through designing for disassembly?

We need a lot of research and innovation for new building materials. Concrete is already adding ash to the mix - they’re trying to design better in the concrete and cement factories, because they understand they won’t be able to play the game for much longer. If you design for disassembly you will definitely have a secondary market for building materials. I am very keen to use bio construction, but of course buildings have different scales. For my net zero house in Spain, I can use hemp block for the structural wall, so I don’t have pillars or columns or anything with concrete. The hemp blocks are made of hemp which is similar to straw. I can also use wood (I also have to take note where I source the wood from). All this is easy to do in a small one storey or two storey house. You cannot do this in a city in a condominium. There has to be some research done on how to implement this kind of low impact construction materials and techniques into skyscrapers. There has been a lot of research into the performance of wood in making high rise buildings, up to 17-18 storeys tall. There is so much more we can do, it just hasn’t been a priority in research.


Another thing is how to make existing buildings and cities circular, more efficient and sustainable. It is an enormous task. They have already been built with bad design and performance. You cannot do it with architecture alone, you need to engage a lot of people. Here’s an example - if you have a lot of cars operated by batteries and the batteries get charged in the parking lots of buildings covered by solar panels, when the energy is in surplus, you can charge the batteries. Why don’t we put solar panels in all the highways? Everything made of asphalt creates this heat island effect because it’s really dark and dark colours attracts and stores heat more intensely. Any parking lot in Singapore that has no tree - can we cover it with solar panels? Can we use empty spaces on buildings for farms or solar panels? There’s so many things you could do to produce this clean energy.


You need to make everything interconnected because there will be some moments when energy demand is very high and some moments when supply is very high. You will need batteries to store the extra energy, and you could implement that in the transportation system. You could link all the buildings together so they can share energy. The way we’ve been thinking of cities is buildings, buildings and more buildings with arteries of roads, and pedestrian paths for people to move. But right now, we need to consider that all of these buildings will be connected in a super-web of energy and cables and sharing of signals - making it smart but in a city scale.


The key is to also add a lot of green. Cities need to be green. Green rooftops and green trees everywhere. Stop paving every single floor - you need to let the floors breathe. Soil plays a huge part in not only temperature but also evapotranspiration, and breathing, and even absorbs a lot of CO2. Soil and open green pavements. Sandy pebbles, concrete that is porous, anything that can allow for the water to go through, and go into the aquifers is essential. There are so many things that need to be done, and everyone, from politicians to architects, engineers and even us as users can get involved.


How do we close the loop for building energy and water demand?


A closed loop for water already exists in nature. I don’t know how we have not achieved it yet. First, all the grey water that comes from showers and sinks should be completely separated from sewage. This is because it’s much easier to clean grey water than to clean sewage. All of that should be all cleaned.


People often use a lot of water for things that they shouldn’t. Even in the way we have designed our water systems - we don’t treat the water at all. We just dump it out. It is really simple, you can actually clean through gardens which will be beneficial for the plants too. Cities should be cleaning 100% of all the water and recycling 100% of all the water. They should be allowing infiltration of water from storms as much as possible. The moment you pave and cover everything - imagine you start putting superglue on your skin, when you take a shower, it won’t even touch your skin. This is what we’re doing with cities and urbanisation.


That has a huge impact on temperature, on the well-being of soil and also stormwater management. Now we have huge storms, the water doesn’t have anywhere to go, and there are floods everywhere. This creates huge impacts on our economy and society - even Singapore has lots of floods! The moment you have more permeable flooring, you can have more infiltration of the water into the underground, and we can use it for irrigation. All of this needs to be incorporated to create a circular system.


For a closed loop for energy, it depends on the type of building we are talking about. Homes are not the same as offices. Offices are not the same as manufacturing plants. Then you have hospitals, laboratories, and buildings that have very different requirements for energy use. I think governments should start focusing on primary offices and housing. They are very low energy consuming so it would be really easy to tackle them, whereas buildings like hospitals andr manufacturing plants consume a lot more.


Sometimes you can have a very efficient building but put machines inside that consume a lot - these are called unprocessed loads. Processed loads are all the things that come within the building - cooling, heating, pumps for water. but unprocessed loads are all the things you plug in the building. Imagine a data centre with a lot of servers. These servers are not part of the building, they are machines inside.


That is why it’s very difficult to talk about all buildings in general like that. Some buildings should be able to be net-zero, some buildings like a data centre for example would likely have to purchase renewable power from another source, because within the building they won’t be able to afford all the cooling. It could be possible through innovation of course. But still making data centers in Singapore is like making a monster and trying to tame it down. But if you make a data center in iceland, it makes sense, because it’s so cold all year round. You’re gonna have a much simpler way of cooling the building. But in Singapore it’s very difficult, so sometimes, it’s going to be hard depending on the climate, to ensure circularity and close the loop. But this does not have to be the end because the world is now interconnected - the things that are harder in one country, we can find a solution elsewhere. What we cannot do is ignore the impact, that’s for sure.


Can you tell us a little about your home where you have incorporated several of the strategies we just talked about?


In Lombok, I was a sustainable consultant for CH2MHill, working on industrial advanced technology buildings - airports, data centers, laboratory buildings, hospitals, manufacturing plants. In Singapore, I’ve worked in Novena hospital and in Procter & Gamble Innovation Centre Lab. I also worked in Medina airpot in Saudi, in many projects with Coca Cola and Pepsi. In these buildings, because the processed loads are so high, you cannot reduce a lot of the total overall building consumption. Even if you make the processed loads net-zero, the unprocessed loads are still going to be huge. It’s a lot easier here in Lombok.



The first thing I was going to do in Lombok was our house. I was still in Singapore and I thought I had to do a house where I design for disassembly, minimise cement, make all of my walls using clay, sun-dried bricks (no machines at all to make them), and walls are rendered with limestone instead of cement. We did all of this and we also have bamboo that you can mount and unmount. We use wood from planted forests here that are quite sustainable.



We treat all our waste - we recycle most of our waste here, the ones you can, which is quite a lot. All our organic waste feeds our little black soldier fly colony, with which we feed our chickens, who give us eggs. So we have incorporated a lot of things here. It’s really easy when you’re doing it yourself and you’re committed. But when you’re doing it for clients, they don’t fully appreciate everything. People don’t want to have the bamboo house with no aircon, they want the aircon and the resource-heavy uses. I’ve worked on some net zero projects here, and the clients have so much money, for solar panels and stuff, but then they come and bring energy-heavy machines. In one villa we made, the client brought hairdyers of 2000W each, one for each bathroom. My house consumes like 1 kilowatt. And she brought 5 of those hairdyers. People are not aware of what they are doing. It does not matter if you spend a bomb on creating a net-zero building, the way you use the building - leaving the lights on, leaving aircon on, bringing all these machines, it has a huge impact. A lot of people are not willing to give up those luxuries. Perhaps we will be able to achieve a balance between resource usage and efficiency through smart buildings of the future.


Join us on November 26, Thursday, 4pm GMT+8 to hear more insights on the built environment from Paula. Register here to attend.




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