Should I build a house in a flood zone? A self build expert explains whether or not it's a good idea

As our climate continues to change, flooding is increasingly a concern for homeowners.

For self-builders, flooding can have serious implications, even before a brick is laid. If you’re buying land, flood risk isn’t just a matter of safety, it’s a fundamental part of the planning process. Get it wrong, and you could face delays, extra costs, or refusal of your application. But with the right information and professional support, building in a flood zone can still be possible.

This article explains what a flood zones are, the effects of different types of flooding, and what planning rules you’ll need to know if you find a plot is in a flood zone. It also explains the design options that will protect your home, and what support is available if things go wrong.

What is a flood zone?

In England, flood zones are defined by the Environment Agency and reflect the likelihood of flooding from rivers or the sea.

There are three main zones, from 1 to 3 categories, with the flood risk ranging from low to high respectively. Zone 3 is further split into 3A and 3B, with A being land that’s developable with the right mitigations. B covers areas that serve as natural flood storage – and comes with the most severe restrictions.

It’s important to know that these zones don’t take into account all types of flooding, and that’s where self-builders often come unstuck.

Types of flooding

When we think of flooding, we often picture rivers breaking their banks or storm surges washing in from the sea, but this isn’t the full extent of flooding that occurs.

• River flooding happens when rivers and streams can’t cope with the volume of water, usually after heavy rainfall.
• Coastal flooding is caused by extreme tidal conditions and storm surges.
• Surface water flooding happens when rainwater can’t drain away quickly enough – something that’s becoming common as urban areas expand, and more ground is covered by impermeable surfaces.
• Groundwater flooding happens when underground water levels rise and seep into buildings.

How to check the flood risk

The best place to start is the Environment Agency’s interactive flood map, which shows flood zones, surface water risk, and historical flooding. It’s free and easy to use and you just need a postcode.

Local planning authorities (LPA’s) also have their own Strategic Flood Risk Assessments (SFRAs), which can reveal vulnerabilities not shown on national maps. To make sense of this information, especially when buying a building plot, its best to commission a Flood Risk Report from a specialist consultant.

Why build in a flood zone?

It’s quite common to build in flood risk zones for a variety of reasons.

Planning policies often require new homes to be built within existing settlements and unless the risk of flooding is high, development will be allowed under certain conditions such as replacing an existing house. In some cases, the land may have an historical planning permission that was granted before the risk of flooding was known.

Whilst planning policies may not always restrict development, it's still important to ask if building in a flood risk area is a good idea? Likewise questions should also be asked when considering buying a house in a flood risk area.

Of course, when looking for land, it's best to search where flooding is not a problem, however, if you already own the land you might not have any alternative. It’s therefore essential that you know the risks and include mitigations to keep your home safe.

Planning rules for building in flood zones

If you’re planning to build in a flood zone – especially Zones 2 or 3 – you’ll face stricter planning controls. In these higher risk zones, LPA’s will apply a ‘sequential test’ which asks whether the development could reasonably be located in a lower-risk zone. If it can’t, they’ll grant consent on the basis that the wider sustainability benefits outweigh the flood risks and that these risks can be managed.

This is where a Flood Risk Assessment comes to prove the mitigations required and satisfy the exception test.

A Flood Risk Assessment (FRA) is a key part of a planning application for new developments. The FRA must demonstrate how the development will remain safe over its lifetime, how flood risk will be managed, and how it won’t make flooding worse elsewhere. It considers the available flood risk data and assesses the site levels against forecast flood levels.

Designing a build for a flood plain

Building in a flood risk zone requires good quality design to include the essential mitigations and provide flood resilience.

When building a new home, the best starting point is to raise the floor levels above expected flood levels. This mostly involves building up the ground floor slab. If flood water displacement is required, it might be necessary to build on stilts or allow the flood water to enter the substructure. This will require drainage systems to have non-return valves to prevent floodwater backing up through toilets and sinks.

When extending or converting existing buildings, raising the entire floor level may not be possible so consider split-level floor plans to elevate critical living areas. The challenge is then to build a home that can withstand flooding by resisting water and recovering quickly, following a flood.

Durable construction materials are essential as they drastically reduce the impact of a flood and make recovery much faster. Concrete, bricks, and cement-based render all perform well in wet conditions. Timber is also a good as it quickly reverts to its original condition once flood water recedes.

Internally, ceramic floor tiles and closed-cell insulation will limit damage as they won’t absorb water. The key is to avoid materials that become damaged or soak up water, like chipboard, plasterboard or laminate flooring. It’s also a good idea to raise electrical sockets and appliances well above the expected flood level to limit the risk of damage.

Flood readiness and mitigation

Even with a well-designed house, it's still wise to prepare for the worst. Signing up for flood alerts is a must, so register for alerts from the Environment Agency. Have sandbags on hand to respond quickly during a flood event. More sophisticated options like flood boards, airbrick covers, and door barriers offer better levels of protection.

If your home is damaged by flooding, check if you’re eligible for the Build Back Better scheme. The scheme provides up to £10,000 on top of reinstatement costs to install flood prevention measures. This could pay for installing flood doors, raising electrics, or replacing floors with more water-resistant options.

Insurance and financial implications

In a high-risk area, insurance may not be available or insurers may offer cover but with high premiums and large excesses. To help, the government and the insurance industry set up Flood Re, a scheme that makes affordable flood insurance for qualifying homes.

But – and this is a big but – Flood Re only applies to existing properties built before 1 January 2009. If you’re building a brand-new house in a flood zone, you probably won’t qualify.

This all means that you’ll need to find specialist insurance, which could cost significantly more than a standard policy. And if you’re planning to sell the property later, limited insurance options can affect saleability.

FAQs

Can I build in a flood zone if I raise the house above the flood level?

Possibly, but planning consent will still depend on the sequential and exception tests and a Flood Risk Assessment will be needed to demonstrate safety and risk mitigation.

Will building on stilts mean I don’t need flood insurance?

Not really. Insurers look at postcode, historical data, and Environment Agency classifications. Even if your house is elevated, they may still consider the area high risk.

Is building in a flood zone ever a good idea?

In most cases, it’s better to avoid it. But if you have no alternative, or you’re converting or extending and existing building, it can be done with the right precautions and realistic expectations.

If you are still on the hunt for a building plot, check out where to buy land as well as plot buying mistakes in our plot-buying pieces.

Meanwhile, if you are considering buying garden land from a neighbour to build a house it is worth reading up on whether or not you need to pay stamp duty on a building plot.