Are Amphibious houses the answer to flood prone areas?

For years this was treated as an eccentric idea, the kind of thing that turns up on television once a decade. The housing numbers have changed the conversation. The Environment Agency puts 6.3 million properties in England in areas at risk of flooding, and around one in nine new homes built between 2022 and 2024 sits in an area of medium or high flood risk. Britain is going to keep building near water. The question is how to do it without the water winning.

We first published this article in 2017, when the UK had exactly one amphibious house. Enough has happened since that we have rewritten it from scratch.

How amphibious houses work

The principle comes from boat building. The house sits in a concrete dock set into the ground. Its base is buoyant, usually a concrete hull, so when the dock fills with floodwater the whole structure lifts. Vertical guide posts, known as dolphins, stop it drifting sideways. Services stay connected through flexible pipework; Baca Architects call their version elephant cabling, with pipes that extend by up to three metres without disconnecting.

The house only moves when there is a flood. The rest of the time it looks and behaves like any other home, which is also what separates it from its cousins.

Floating, amphibious or stilts: what is the difference?

A floating home sits permanently on water, like a houseboat with better insulation. An amphibious house spends almost all of its time on dry land and floats only during a flood. A house on stilts or an open undercroft never moves at all; it is simply built with its floor above the expected flood level. The three get muddled constantly, including in planning discussions, and they have quite different planning, engineering and insurance implications.

The Grand Designs amphibious house, ten years on

If you have seen an amphibious house before, it was almost certainly Formosa, the house featured on Grand Designs in 2014. Baca Architects designed it for a small island in the Thames near Marlow, replacing a bungalow that flooded over and over. It was the first amphibious dwelling to win planning approval in the UK, on a plot in Flood Zone 3 and a conservation area.

The 225 square metre house can rise up to 2.7 metres in its dock, comfortably above predicted flood levels for the site. Its terraced garden doubles as an early warning system: the lowest level floods first, then each higher terrace in turn, so the owners can read the river's mood from the kitchen window.

The world's largest amphibious house is on its way, and it is British

The concept has stopped being a one-off. Baca's Misty River House, a 385 square metre replacement dwelling on a riverside plot near Henley-on-Thames, won approval from Wokingham Borough Council despite sitting in the green belt and in Flood Zone 3. It is designed to rise around 2.4 metres in its dock, built from an oak frame with lime-rendered insulated panels, with construction due to have started in 2025. When complete it will be the largest amphibious house in the world.

Two things make it interesting beyond the scale. It shows a second English planning authority approving amphibious construction in Flood Zone 3, which turns Formosa from a curiosity into the start of a precedent. And like Formosa, it replaces an existing dwelling, which matters more than it sounds. More on that below.

The Netherlands got there first

None of this is new to the Dutch. At Maasbommel, on the Maas in Gelderland, the contractor Dura Vermeer built 32 amphibious and 14 floating homes back in 2006, on a recreational lake outside the dikes. The amphibious ones rest on concrete foundations and rise with the water, fastened to flexible mooring posts, and can cope with level changes of up to 5.5 metres.

The Dutch planning bargain was simple: building was allowed on land that floods, provided the buildings could live with it. Twenty years on, those homes are still there and the model has been copied around the world. The UK is arriving late, but it is arriving.

Can you actually get planning permission for one?

Here is where the architecture meets the paperwork, and where most of the optimistic coverage goes quiet.

A new dwelling is classed as "more vulnerable" development under national planning policy. In Flood Zone 3 that means the application must pass the Sequential Test, and in Zone 3a sometimes the Exception Test too. A clever floating design does not exempt you from any of this. If a reasonably available site with lower flood risk exists, the local planning authority expects development to go there instead, however good your dock and dolphins are.

Where amphibious construction earns its keep is the safety case. A site-specific flood risk assessment has to demonstrate that the development will be safe for its lifetime: finished floor levels (national policy expects at least 300mm above the 1 in 100 year flood level, including a climate change allowance), safe access and egress during a flood, and no increase in flood risk elsewhere. A house that rises above the design flood level answers the floor level question emphatically, and because the water flows into the dock rather than being displaced, the floodplain keeps working.

It is no coincidence that both UK amphibious houses replaced existing dwellings. A replacement home on an established residential plot is a much easier argument under the NPPF than new development on undeveloped floodplain. If you are hoping amphibious design will unlock a virgin riverside field, it will not.

The evidence base is also moving under everyone's feet. In May 2026 the Environment Agency added climate-adjusted surface water extents and depth bands to the Flood Map for Planning, and a revised NPPF is expected in Summer 2026 with flood risk as a standalone chapter. Sites that looked clean a year ago may not look clean today.

Weighing up a plot in a flood risk area? This is exactly what our flood risk assessments for planning are for, alongside Sequential and Exception Test reports and NPPF guidance. We have prepared more than 5,000 flood risk assessments since 2014. Request a free quote and a consultant will come back to you within 60 minutes.

What do they cost, and can you insure one?

When Formosa was built, the premium over a conventional house of the same size was put at 20 to 25 per cent, roughly what a basement adds. There are still too few UK examples to know whether that figure has fallen, though the engineering is no longer experimental and the consultant team will not be learning on your project the way they were in 2012.

Insurance is the harder question, and the honest answer is that it depends. Flood Re, the scheme that keeps premiums affordable for flood-prone homes, only covers houses built before 2009, so any new amphibious house sits outside it, and the scheme itself is due to wind down in 2039. With UK flood claims hitting record levels in 2024, insurers are looking hard at anything new in a flood risk area. A house that demonstrably cannot flood ought to insure well, but expect to do the explaining, with the engineering reports to hand.

Flood risk also shows up in valuations and mortgage decisions. If you are buying near water, amphibious or otherwise, a property-specific flood risk survey tells you what postcode-level screening data cannot, and a flood risk assessment for insurance purposes can support the conversation with underwriters.

The alternatives for a flood-prone plot

Amphibious construction is one answer among several, and usually not the cheapest. On many sites a floodable void does a similar job with far less engineering: the building stands on stilts or over an open undercroft, the habitable floor sits above the design flood level, and floodwater passes underneath as it did before the house existed. Raised finished floor levels and water-compatible ground floor uses work on gentler sites. For existing homes, property flood resilience measures, from flood doors to non-return valves, are the practical route, with grant funding available after flood events.

The right choice is site-specific. It depends on flood depth, flow, land levels and what the local authority will accept, which is an assessment exercise before it is a design exercise.

So, are they the answer?

They are an answer. For a replacement dwelling on a flood-prone riverside plot, where the owner wants to stay and the numbers work, amphibious construction is now a proven, consentable option in England, with two planning approvals and the world's largest example under way. For volume housebuilding it is not there yet: the cost premium, the insurance friction and the engineering oversight each unit needs all count against it, and simpler approaches like floodable voids cover most of the same ground.

What has changed since we first wrote this piece in 2017 is the direction of travel. Policy is slowly accepting that we will build near water and had better do it on the water's terms. The Dutch worked that out decades ago. The amphibious house is the most photogenic expression of the idea, but the thinking behind it, design for the flood instead of pretending it will not come, now runs through everything from national SuDS standards to the way the Environment Agency maps surface water.

Considering a flood-prone plot or property?