Flood risk to UK homes is increasing and the latest national assessment indicates that up to 1 in 4 properties could be at risk by the middle of the century. Surface water is a major driver of that change.
This guide explains how to assess flood risk at property level and the practical measures that can reduce damage, based on the same principles used in our detailed flood investigations.
Not every property owner is in a position to commission a detailed engineering study, but there are still practical steps that can reduce damage and improve recovery. This guide sets out the principles used when assessing homes and the measures that can make a real difference.
When we started in 2012 this area was referred to as Property Level Protection. Today it is generally known as Property Flood Resilience, or PFR. The terminology has changed, but the core idea is the same. Understand the risk, understand the building, and apply the right combination of measures.
What PFR Actually Means
An Environment Agency funded study led by Professor Bonfield grouped resilience into three areas:
Resistance
Keeping as much water out as possible using measures such as flood barriers, self-closing air bricks and non-return valves.
Recoverability
Accepting that some water may enter and designing the inside of the property so that damage is limited. Tiled floors, raised electrics and resilient finishes are typical examples.
Reduction
Managing water at the property boundary through drainage improvements, permeable surfaces, rain gardens and rainwater storage.
All three matter. Focusing on door barriers alone is rarely enough.
The Limits of Grant Based PFR
Through our survey work for councils and government schemes we often saw the same frustrations. The funding was helpful but the scope was narrow and the budgets were fixed.
Homeowners would ask about upsizing a culvert, changing site levels or re-routing drainage. In principle those may reduce risk, but they require hydraulic calculations, consent and a check that the work does not increase flooding elsewhere. That is engineering, not a standard PFR grant.
That distinction is important. PFR is usually about the building itself. An engineering driven flood mitigation strategy looks at the whole site, but would be a more costly private instruction.
Start With the Flood Risk
Before looking at measures you need to understand:
• The source of flooding
• How quickly it arrives
• How deep it gets
• How long it lasts
This affects everything.
A short duration surface water event with little warning needs different measures from a river that rises slowly but remains for days.
The construction of the property is just as important. A solid floor behaves differently from a suspended timber floor. Listed buildings have constraints. Masonry type affects how quickly water can pass through the wall.
Your own circumstances matter as well. If you are often away from home, a demountable barrier may not be viable. Budget will influence whether you are looking for simple measures or a long term strategy.
Making Resistance Measures Work Properly
Typical resistance measures include:
• Flood Barriers and doors
• Air brick covers or self-closing air bricks
• Sealing service penetrations
• Non-return valves on drainage
There are also some straightforward improvements that are often overlooked, such as sealing around existing door frames, with many properties having a clear gap beneath external doors that allows water to enter at low depths.
What is often overlooked is water passing through the wall itself.
Laboratory testing by Safeguard Europe showed that repointing with a waterproof additive (Additive No.2) and applying a suitable masonry treatment can reduce the rate of water in a 600mm deep flood passing through a single skin brick wall from around 12.5 litres per square metre per minute to less than 0.2 litres/m2/min.
That is a significant improvement and it can make door barriers far more effective, by helping to waterproof the structure they are fitted to.
Low level masonry is one of the most common flood ingress routes. Repointing and applying a breathable water repellent can significantly reduce the rate of water passing through the wall and improve the performance of resistance measures.
Floors, Groundwater and Internal Water
Water does not only come through doors.
It can:
• Rise through the ground
• Track through the wall
• Enter through the drainage system
For suspended timber floors, anti-flood air bricks or air brick covers are a simple but important measure.
For solid floors, water may enter between the gap between the wall and the floor.
Enhanced PFR
Internal tanking as a form of negative waterproofing is sometimes used after a flood when a property has been stripped back, but it is not suitable for every building and needs careful consideration.
Pumps and the Reality of Managing Internal Water
The role of a pump is not to keep a house completely dry during a flood. It is to keep water levels low enough that clean up is manageable and damage is reduced.
Common problems we see include:
• Float switches that cannot operate at low water levels (where a chamber hasn’t been installed)
• Pond pumps used for flood duty
• No redundancy (i.e. no spare)
There are two typical approaches:
• Portable puddle pumps for low level water
• Installed packaged pump stations for automatic operation
Always allow for backup. A single pump is a single point of failure.
Recoverability Is Just As Important
With Flood Re scheduled to end in 2039, the ability of a property to recover quickly without a full insurance claim becomes more important.
Measures such as:
• raised electrical services
• resilient wall finishes
• tiled or concrete floors
• removable kitchen units
can significantly reduce long term cost and disruption.
Looking Beyond the House
In some locations the most effective solution is outside the building. A flood wall or changes to site drainage can transform the level of risk, but these require proper design, ground investigation and hydraulic assessment to ensure they are safe and do not transfer the problem elsewhere.
That is where a detailed engineering study becomes necessary.
A Realistic Way to Approach PFR
Every property is different, but the decision process is always the same:
- Understand the flood mechanism
- Understand the construction
- Be clear on budget and expectations
- Apply the right combination of resistance, recoverability and reduction
Even small, well chosen measures can make a meaningful difference.
Preparedness
Preparedness is just as important as physical measures. Signing up to the Environment Agency’s flood warning service, understanding how quickly flooding could occur, and having a simple plan for what to move, what to deploy and when, can make a significant difference to the outcome. Many resistance measures rely on timely installation, so knowing your trigger point and keeping equipment accessible and maintained is a key part of Property Flood Resilience.
Why We Are Sharing This
The engineering team at FPS Environmental Ltd undertakes detailed flood investigations and mitigation strategies. That work is senior led, time intensive and not always what a homeowner may be looking for at this stage.
By setting out the principles here, our aim is to help more properties become resilient, whether or not a full engineering study is commissioned.