(master-classes on this topic and others, see on the right)
” What is Circular Building really?” , a Dutch journalist twittered, being confused about the debates going on. Its not clear yet, apparently, so lets give it a try.
The word “Building” we all understand, its about the word Circular that is giving headaches. But Circular, in its most basic form, is that you get back what you have spent. In other words: if using a wooden beam in a building, you take care the tree from which the wood came is grown back. In that case you made use of resources i a circular way, the stock has been restored. Fore economists among us: it like a revolving fund, but the real…. Every entrepreneur knows this. If you dont refill the stock, you are soon out of business. Problem with building is that restoring stock is out of sight fro the direct involved parties. Like the regrowing of the three. Do Rumanian’s replant all their forests, or Indonesia?
Circular thus is managing resource ( and energy sources) in a way that restores stocks, and does not depletes these.
Therefor, circular building is not in fact about buildings, but about managing resources, a mistake often seen: a building in itself cant be circular or not, its the resource flow that counts . The building is merely a temporarily storage of of resources, a resting point in a constant flow through the system. Of course the longer stored, the less burden on the natural flow , giving room for other uses . Like new construction. And of course maintaining buildings is part of circular management, reducing the burden on the flow, and reducing re storage need. As long as you stay with the regeneration capacity of the flow, there is no problem.
If on the other hand the volume, speed and (driving) energy of resource use is higher as natural replenished, there is a one way use of resources leading to depletion. To become circular again, measures are needed to restore the stock.
Which counts for all materials and resources (as well as for -processing-) energy, also for minerals and metals ! First lets have a look at minerals: Take clay bricks. That has always been part of a circular process, in the Netherlands: clay bricks where made of sediment, coming down in the rivers, on their way from the Alps to the ocean. A continuous renewing flow. ( mark the renewing, not renewable). De available stock was determined by the volume and speed of the erosion process of the mountains, by rain wind and sun, While the resource is replenished by still regrowing mountains, pushed up by continental drifts and tectonic push ups. You could remain producing clay bricks forever, as long as you stick to the flow coming down the rivers. That is, apart from the energy to burn the bricks, which has to meet the same standards of course: renewable, and actually renewed. That is circular. And of course, also here, you can increase the potential outcome of the flow, by keeping the bricks longer in use, or to reuse them. The speed and volume withdrawn from the flow reduces. Thats what I call linear delaying of the flow in the cycle.
There is , as I wrote before only one kind of cycle, of resources going through the system. The difference between resources is the speed at which that natural cycle flows. By which they are regenerated. Some materials take millions of years for that. But still they have to meet the same standards of evaluation. Which becomes more difficult to explain when we discuss metals. Metals are not renewable, are they? Is the standard reactions, and even concluded in political and scientific rules and regulations. But they are, and they do renew. There is a certain speed at which we could use metals in line with their natural regeneration, But thats so low, its not relevant for us here and now. So we should either use very little of it, or restore ourselves . The metals are not disappeared of course, they are spread and diluted in the background as molecules. Rusted away so to say. Om the front side you can see this, since the ores are less and less saturated, which requires ever more energy to process. See the graph: we are now on the right side.
The stocks of metals can be restored, man-made, for instance by collecting molecules from the background, like via filtering of ocean water. Since all ends in the sea ( think of plastic as well, that we want to filter from the oceans) And yes that will cost huge amounts of energy, there is no free lunch. But in a circular approach, the energy for restoring should be counted for. As I argued before, its a form of unequal treatment of resources, resource racism, if biobased resources include restoring in their evaluation, and metals don’t , only since some people keep shouting that its non-renewable. 
In fact you could easy summarize this , saying that the longer the cycle time of a resource, the higher the impact, of materials and (driving-) energy together.
Back to building. Design and building is therefore in fact a physical exercise: which resources to use, where to get them, and how do I assure they don’t deplete. The most easy and simplest way is to use biobased resources. Which have the least impact in the linear part: in production and processing they require limited energy input, which also can be renewable and renewed, at first of course by the use of solar radiation for the grow and restore route. Which by the way does not imply the stock is infinite, there is limited space-time on earth available ( productive ha’s ). So also here, the longer in use the more profit for all.
However the choice for biobased should be the last step in a process, preceded by some higher scale level questions, to alleviate pressure on resource cycles. . First of all: can we avoid building as such? As I once proposed for a a sustainable built housing area, that had many visitors . They asked for a sustainable Hotel-Conference facility. After some asking around, it turned out there were enough small and medium sized rooms available in walking distance offices, And also enough empty rooms with house owners, that were willing to rent out in airbnb style ( which then was not yet invented…) Combine the two in smart way, and you have a hotel-congres-facility without having to lay one brick. Which was back then one step to far for the local organization, but there are possibilities… Or we could ensure people move to the south of the Netherlands, a shrinking area, where there are many empty houses which will be demolished soon. That also is circular thinking. Or better, circular ‘sheltering’ people and functions.
But then, if a building is unavoidable, can the required function be provided in alternative way? A combination with another project, or as service? And if a new building is constructed, can it be made with as little materials (and energy) as possible? More advanced space lay out, double use of space, compartmentalization, partial heating , etc? That are all questions to be answered before actual construction, required to bring material and energy flows back within circular operation, ans also to reduce CO2 emissions .
Only then comes the actual choice of materials, and in fact, the only way to have a chance to establish a real circular approach is to use biobased materials. And lets be honest, for buildings we can do without most metals, (as many wooden buildings of all sorts proof nowadays) and certainly without aluminium in a building. There are many fine alternatives for that, which will save us the very energy intensive production and re-stocking route. The mantra is usually: use non renewables as efficient as possible, but it should be: use non-renewed resources as little as possible.
Well, Circular it will be, and to summarize this in somewhat less words: Circular building ( or renovating) is using resources ( and the energy for this) with a speed that assures that flows remain flowing. Or can be regenerated, and will be regenerated.
Which first and for all is a matter of space and time: How much resources per time period ( volume speed, energy, restore capacity) are available, and how to optimize their use. Always in a combination of linear delaying and circular restoring, on different scale levels for “ sheltering”
In the end, its biobased building that provides the largest potential, and as I advocated earlier : the future in fact will be vegetarian building….
(picture: Tree cathedral Italy http://www.giulianomauri.com/test/ )