How Stolon Studio’s Stables Yard housing has been designed to withstand flooding

The Building Regulations make no requirement for flood resistance (or resilience), but the serious consequences of flooding mean that it should be a consideration in every building project, argues Stolon Studio co-founder Robert Barker, particularly as climate change increases future risk in ways that can be hard to predict.

At Stables Yard, a six-house development the practice recently completed in Beckenham, south London, flood resilience is provided by both the architecture and the landscape design.

Here, he explains the strategies used and the precautionary and creative approach the practice adopts to water management in every one of its schemes.

How did you assess the flood risk at Stables Yard?

An assessment was required for planning as the site has what’s called a ‘medium’ probability of flooding. But we would always carry out this kind of assessment, even for small projects where it is not mandatory. A good place to start is the government’s freely accessible online floodmap for planning, while more detailed information is available from the Environment Agency, showing evidence of historic flooding as well as climate change predictions. It provides several scenarios and we advise clients to work to the more extreme ones. For instance, the legal requirement in East Anglia is to design to a one in 100 year flood level plus an 11 per cent increase in flows, but on a recent project there, we tested the design to more extreme events - one in 200 years plus 65 per cent, while for another one, we worked on one in 1,000 years plus 25 per cent.

At Stables Yard, the data shows the current risk is not great, albeit becoming more significant with climate change. The main threat comes from a nearby culverted watercourse – which doesn’t, in fact, register in the data – and from surface water, for which there is much less historical data than on river flows and coastal flooding. It’s harder to model the effects of surface water flows as they can be affected by land-use changes or even temporary obstructions, which also suggests that a precautionary attitude is appropriate. We witnessed this first hand in the West Midlands, this December, where there were areas flooded that were not predicted to on the government site.

As I’ve worked a lot with buildings on or near water, I’m always thinking about how it behaves, noticing subtle differences between low and high ground. Stables Yard occupies a sloping backland site that is slightly sunken relative to surrounding streets – as many such spaces are.

How have you mitigated that risk?

The first principle is to ensure safe access to and from the site in the event of a flood. Having demolished existing buildings we resculpted the land to ensure a pathway towards safety for residents along the driveway that leads from the street to the houses. The buildings are set above flood level, and surrounded by a shared deck which could also provide a kind of refuge for residents. One in 100-year projections plus an allowance for climate change are for about 350mm deep floodwater in place. This isn’t very high in the context of some sites we have worked on, but would still cause a lot of damage and disruption – and could, of course, be an underestimate – so the deck is placed 700mm above ground level.

As the houses rest on screw piles rather than a big concrete ground beam, water can flow underneath to the lower part of the plot. We always think holistically about design, and our response to flood risk suggested a lightweight structure. This also has benefits in terms of embodied energy. Overheating is another growing risk and is addressed through shaded windows and stack-effect ventilation.

There is an attenuation tank which stores excessive surface water run-off before gradually releasing it back into the sewer system. But a greater potential threat comes from the culverted watercourse which carries a high volume of water. By re-forming the lower part of the gardens we have increased the volume that might act as flood-water storage by 55m³. Overall, there is a kind of hierarchy to the site plan, with some areas protected and others – including parking – allowed to flood. If every new development increased storage capacity in that way, the risk to whole areas would be reduced.

Wherever possible, we’ve tried to deal with run-off at the ground level, rather than relying on the attenuation tank. The deck, parking area and gardens are all permeable surfaces. The bike store has a green roof, but we didn’t put green roofs on the houses, in part due to the quantity of self-seeding trees nearby. Instead, they have a pitched form that supports photovoltaic panels and creates a generous volume in the upper floors, which helps combat overheating.

You’ve worked a lot in flood-prone areas. How does Stables Yard relate to that work?

A lot of it is driven by the idea of creating better integration between architecture and its environment, and better drainage. SUDs (sustainable drainage systems) sounds unexciting but in the context of design, it can be. The Australians have a better term: water-sensitive urban design. Today the common approach is to install drainage pipes to an attenuation pond on the edge of the development, but why not make water central and integral to placemaking? We need to learn to love those muddy brown spaces that are so good for wildlife and for the water environment.

At Hampton Quay, a 105-home waterside scheme we won consent for in Littlehampton, we created sociable spaces – shared courtyards and parks – that also provide part of the water solution, attenuating rainwater run-off from the roofs. With our 215-home Garrison Gardens scheme at Shoeburyness in Essex, the risk is so extreme that we created ‘islands’ of development surrounded by a flood-absorbent landscape. Flood risk and spaces for water should be central to the thinking in every project, and the response can make places that are more interesting and popular than would otherwise be the case.

At Wensum Edge, a larger development on the riverside in Norwich that is currently in planning, we’ve created housing clusters around shared spaces for informal play or food growing. Higher areas are drier and safer, while those lower down can accomodate the river as it expands. Houses are all on terra firma but some apartment blocks can flood underneath, in the same way as Stables Yard. 

Does increasing flood risk mean that these kind of measures will become commonplace?

The Environment Agency’s projections for properties threatened by flood have risen significantly in recent years, largely in response to surface water risk. But rather than focus on numbers or individual risk, my view is that everyone should do their best to make more resilient communities. Flooding effects far more people and properties each year than fire yet flood resilience is not embedded in regulations.  Policy could require, for example, that the first half-metre of every new building should be resistant, which would in turn prompt door manufacturers to improve seals, reducing cost and raising standards.

Architects could start to think in that way now, and there is good information available from bodies like the National Flood Forum and the BRE, as well as other professionals. Why not design planting areas to absorb water and protect from runoff, or use a waterproof insulation in the base of a cavity wall construction, and raise the damp-proof level from 150mm to 500mm? Again, it’s a sensible precautionary approach - especially given the unpredictable nature of surface water – but more broadly, we can change the mindset so that flood-resilience loses its stigma, and everyone is doing something to reduce the risk to all.