Case Study: Amphibious House

Situated on the banks of the River Thames, Formosa is the UK’s first amphibious house. An amphibious house is a building that rests on the ground on fixed foundations but, whenever a flood occurs, rises up in its dock and floats there buoyed by the floodwater. Using the latest technology, the property is a major breakthrough for British architects and engineers who have been searching for many years for a solution to mitigate the risk - and damage - of water ingress to homes in flood-prone areas. The new house has been designed to cope with up to 2.5m of floodwater, well above the predicted flood levels and future projected flood levels for the area. A carefully laid out garden also acts as a natural early warning flood system.

The truly unique 225sqm house is located just 10m from the river’s edge. Designed by Baca Architects, specialists in waterfront architecture and floodresilient aquatecture, the house is located on a small island along a picturesque stretch of the Thames in Buckinghamshire, a site designated as Flood Zone 3b and a Conservation Area. While the house is a modern, highly insulated, low-energy building, including large high-performance windows, the architects have ensured that it is also sympathetic to the locality; a scenic spot with very strict planning guidelines. The property has a pitched roof to complement the irregular roofline of neighbouring homes and an overall footprint that is no larger than the old demolished property. The cost of building this type of amphibious home is only slightly higher than a similar home with a basement, due to the outer layer of foundations and the high water table during construction. However, construction costs are expected to fall as builders and manufacturers get to grips with the much wetter weather phenomenon and embrace new thinking and technology.

The client:
“We have always dreamed of living in a house on the River Thames - it offers the potential of a relaxing home in a beautiful setting. We were aware that the site was at flood risk and had the option of converting the pre- 1945 bungalow or building an alternative. The beautiful setting convinced us that we could build our dream home and that we just needed to find a solution that would enable us to do so. Research led us towards floating technology and finally the amphibious house design.’’

Baca Director Richard Coutts said:
“People have always enjoyed living by water. Our senses are stimulated by the wind and soothing sounds of the flowing water and its associated wildlife, along with the play of light reflections of its surface. Others enjoy fishing, canoeing or sailing activities. The aesthetic, environmental and recreational benefits attract a premium for dwellings in waterside locations and, despite the price premium, these properties are often vulnerable to flooding and flood damage. Ideally riverside communities should be designed to take flooding into account, rather than just the odd house, in order that consequences can be mitigated for all. Amphibious design is one of a host of original solutions that will enable residents to live safely by water without worry and have a property which will adapt to the challenges of climate change.”

“Historically most communities have looked for water to build their settlements around. This decision comes from both a practical point of view as well as a more romantic one. Water stimulates our senses and it also has environmental and recreational benefits. Even though watersides are often vulnerable to flooding these are still desirable locations for people to build their homes. With the unpredictable impact that climate change will have on our environment, and the most visible aspect being flooding, a new approach to building and planning around these would be desirable in all cases."

"Marlow’s Amphibious house is a case in point of technology and design coming together to offer a solution to a problem each day more present in our cities and towns. Being the first Amphibious house in the UK it was a challenge to get it built. A considerable amount of effort went into technical research as well as dealing with the relevant regulatory bodies to finally make a success of it. Although this is an isolated intervention it is proof that flood conscious architecture is feasible, we call this Aquatecture. The Marlow House opens a new way of building with water, instead of against it.”

Structural Engineer Matthew Wells, Techniker:
“The house is designed as a free-floating pontoon. A lightweight superstructure is supported on a concrete base with sufficient ballast to ensure stability and adequate freeboard. The floating house is secured by four dolphins (permanent vertical posts) arranged close up to the sidewalls. The assembly is sited within a wet dock comprising retaining walls and base slab. When flooding occurs the dock fills with water and the house rises accordingly.”

Baca Architects:

Baca Architects has established a core specialism in waterfront and water architecture with an award winning
research arm, exploring integrated environmental design, climate adaptation and flood risk management. Baca bring the latest in national and international approaches to water related design through their work and experience in the UK, Netherlands, France and the USA.

Are there other sustainable features to the design?

• high performance insulation
• double-glazing
• external blinds
• heat recovery ventilation system
• solar panels
• intuitive landscape

Why did you come up with the idea of an Amphibious House?

Options for the site included either a floating or an elevated property. A floating property would be near to the river and the adjacent garden but would be in the river course - which was not allowed by the Environment Agency at this location. An elevated building would be set high enough to avoid an extreme flood but has the disadvantage of being almost a storey away from the garden. An amphibious house solves these issues by allowing occupants to enjoy their garden and only rising to avoid floods when necessary.

What amount of water is the house resistant to?

In an extreme flood the house, a 1 in 100 year event, the house can rise over 2.5m.

Has anyone ever built a house like this before?

Similar properties have been built in Holland and New Orleans but this is the first in the UK.

Can the house be swept away in a major flood situation?

No, it is tethered by 4 strong columns that act as mooring posts in major flood.

How do you envision flood-resilient houses of the future?

We envisage large communities that are holistically planned to be better prepared for flooding and climate change. Dwellings will be low carbon, and organized around multi-functional landscapes that will help control surface water flooding or act a large flood storage areas. New communities will be made up of streets of flood resilient dwellings located on the highest ground with amphibious homes located in the transitional zones between development and the natural environment. The long term goal is to design communities that function as normal, preserving continuity of daily life during droughts and floods. Our intention, through our research and built work is that we can demonstrate that the future is not far away.’

What other factors will see more flood-resilient houses built in the future?

Amphibious houses, sometimes known as ‘can-float’ homes, are a new phenomenon in the UK. As the cost of flood events start to have a more significant bearing on the public purse and the insurance secure demand higher levels of protection from the individual, flood resilient homes will become more common place.

Is there a vertical rail-system to keep the house from tilting?

The dolphins (vertical rails) connected to the wet dock combined with ‘control gear’ connected to the house prevent the house from tilting.

Buoyancy and total weight must be in balance – how did you manage this? And how do you keep the house in future from getting overweight?

The can float house also has additional ballast in its base. The house will be floated in a test bi-annually and less or more ballast can be added to or taken out of the base depending on what the client has loaded in the house (such as a grand piano of lots of book shelves).

Has the “hull“ any special requirements in stiffness or torsion?

The base has been engineered to be heavy and stiff. The will prevent the house from bobbing around and to resist the impact of floating Debris such as a tree trunk or floating car during an extreme flood.

How fast does the house react on upcoming floods – or: Is the house also a solution for floods as results of heavy rains and uprising rivers?

The house is located within the middle catchment so water levels will rise and recede slowly.

How many levels/ terraces does the garden serving as an early warning system have?

Three levels.

How far away is the house from the shore line?

8m.

How far does the water level need to rise before the house starts floating?

Approximately 2m.

How far can the water level rise before the house is affected?

The house will begin to rise when flood waters reach around the level of the middle tier of the intuitive landscape. The maximum predicted flood level is approximately 1.8m above ground level but the house is designed to travel up to 2.7m in its current configuration. The house will start to rise when flood cell 2 ( of 4) is inundated.

Is the house protected against driftwood?

A weir is located upstream that will filter large debris plus the heavy base is designed to withstand waterborne
debris.

Is the work on the first amphibious house completed?

Formosa is the first house in the UK to secure planning and to be built of the amphibious house variety. We have now completed a  second amphibious house in Salcombe and more are planned.

Would it be possible to use the technology and build more inexpensive houses for people in developing countries where the danger of flooding is much higher than in Europe?

The house is buoyed by Archimedes principle so can be replicated in high tech or basic
forms. The key issue is the velocity of river flows and ensuring that either the house is sufficiently robust or that lighter weight versions are protected from water borne debris by being located in a protective zone.

How do the owners get in and out of the house in case of a flood? Is there a bridge or anything leading to the entrance? Do you have a picture showing the side of the house where the main entrance is?

There are approximately 20 existing dwellings on the island. All of the owners are required to be signed up to the UK Environment Agency’s flood warning system that requires everyone to leave the island if a major flood warning alert is issued. Thus based on UK policy, occupants will have left the island in advance of a flood. Notwithstanding the house, the house has a secondary sanitation and energy system so should residents be isolated on the house (if flood warning doesn't reach them), they can live onboard with no reduction in services for approx. 8-10days. In Holland this is different and in our proposals for the Dordrecht flood proof pilot inhabitants are allowed to stay in their houses during a flood, and safe access and egress is provided by walkways that are elevated above the predicted flood levels.

How are the services, such as electricity and water, connected and how do they continue functioning in a flood?

All services are connected via flexible pipes that rise with the building- up to 2.7m if ever needed.

Is the house ready yet? There’s an article from October 2014, stating that the owners will move in „by the end of the year“ - so I presume they did so a couple of months ago?

The owners moved in in January after a second floatation test was completed.

Is the cost of the house a secret? If not: would you tell me?

The house cost approximately 20% more than an equivalent traditional house with a basement. The benefit now is that the owners now can insure their property at a reasonable price and it is floodproofed for the future.

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