What’s stopping us from designing the most sustainable building?

If you had a completely empty site and you were going to build the most sustainable building that you could, where would you start? You can control everything, so you can make all of the most sustainable decisions. You can specify anything you want, trial something new, choose sustainable materials… The world is your oyster. Or is it?

Firstly, we’re going to need a brief: what are we building and why? For the sake of this argument, let’s say we’re building housing and that we have a well-located site with limited ecological disruption. To get started we’d need to decide how to orientate our building so that we could maximise natural light and make use of passive heating and cooling to minimise energy use.

Next, we need to decide how much of our site we’re going to use up. Is it better to build a taller building and retain some green space on your site, or build something which has a greater plan area but requires shallower foundations?

Typically, foundations need to be constructed in concrete and account for a large amount of the embodied carbon of the building, so minimising foundations seems like a sensible decision, but building a little bit taller allows for a greater plan area for your carbon output. Most estimates suggest there’s a sweet spot at about 4 or 5 storeys where the carbon is minimised and the area is maximised.

Once we’ve decided on a sustainable foundation system, we need to consider our structural system above ground. Reused materials offer the best opportunity to construct in a way that we’re used to whilst limiting the embodied carbon.

CLT floor slabs supported by a steel frame constructed using reused steel would allow us to achieve the 4 or 5 storey building that we’re aiming for. To get the best from the structure we’d need a regular column layout with limited column spacings, which could have a significant impact on the layout of our residential building.

What about cladding? We need something that provides a good amount of insulation in the winter but allows heat to escape in the summer.

It needs to be resilient, but also lightweight (otherwise the structure needs to increase significantly to support it) and ideally have details that limit thermal bridging without requiring significant additional structure. Panels made from recycled materials or with the ability to be reused at the end of their lifetime would offer the best solution.

There’s still so much further that we could go

Once we’ve sealed the building, we need to consider how we treat the outside. Adding PV panels on the roof would reduce the energy requirements for the building, but the panels themselves have a significant upfront embodied carbon.

Plus, if you cover the roof with PV, opportunities for urban greening or communal spaces become more limited. Balancing some PV and some planting is probably best, as long as the planting isn’t too heavy, as this would increase the structure required.

But is this really the best we can do? Everything that I’ve proposed here makes use of conventional approaches to construction and materials that we typically build with today. There are challenges associated with all of these ideas, but buildings designed using some or all of these principles already exist.

And there’s a reason for that. We’re limited by cost and programme. We have to design within a set of design codes. But that doesn’t mean there aren’t more innovative methods that we could be using.

What if we didn’t use a conventional foundation system and instead used something more unusual like vibro stone columns or timber piles? Or maybe we could consider something that could be removed in the future, like a steel screw pile?

If we allowed for larger columns, could we construct the building from timber? Or stone?

What if we completely changed the structural form and used arches or vaults that are much more efficient? Could we consider cladding panels that use more natural insulation like hemp or mycelium?

There’s still so much further that we could go.

And really, I missed the most important question right at the start: was there an existing building that we could have reused instead?