Reducing the ingress of flood water into a property

Published: January 15, 2025

Generally speaking, when we think about Property Flood Resilience (PFR) measures, our minds often go straight to flood barriers, self-closing airbricks, and non-return valves. For area prone to groundwater flooding, sump pumps may also come to mind. In cases of flash floods that pass quickly, these solutions are often enough to keep water out. But what happens when floodwater lingers for longer periods? Many people report that their flood barriers have “failed” after prolonged flooding, but in most cases, the barriers themselves haven’t failed. Unless they were fitted poorly or overtopped, the real issue is that water will find it’s wicked way into properties through less obvious vulnerabilities – like the walls.

On one occasion, after a flood left my home stripped of plaster, I was flooded again just a few weeks later and this gave me the unsettling opportunity to witness firsthand water entering my home through the walls. It was as if someone had turned on multiple taps all at once!

Ways to Reduce Wall Ingress

If water ingress through walls is an issue, there are several ways to try and prevent this from happening:

Check Your Mortar

Inspect the condition of your mortar, especially in older properties. If it needs repairing, opt for waterproof and breathable mortar to reduce water penetration.

Apply a couple of coats of waterproof and breathable cream paint solution to the exterior walls. This solution is invisible once dry but will significantly reduce the amount of water that enters your property.

Don’t forget to check the area where the wall meets the ground – it’s often a weak spot or in a state of disrepair.

Apply a Fillet or Tanking System

After a flood, if your property is stripped out, apply a fillet of waterproof slurry internally where the walls meet the floor. This is a weak spot and often a common entry point for water.

Consider a tanking system to limit water ingress. This is best installed by a professional flood resilience company.

Upgrade Internal Materials

Use waterproof and breathable plaster for walls.
Install water-resistant plasterboard (often referred to as “Dragon board” made from Magnesium Oxide). While more expensive than standard plasterboard, this can be used up to the anticipated height of flood depth and then finished with standard plasterboard above to keep costs down.
Also, don’t forget to use closed-cell insulation, which is designed to withstand flooding.

Consider Ceramic Wall Finishes

Some homeowners apply ceramic tiles over a tanking system for extra protection.
There are many varieties, including modern tile designs that mimic wood or other materials, so they don’t look obtrusive.
Importantly, don’t forget to use waterproof adhesive and grout.

Coupling PFR Measures for Maximum Impact

These variety of measures, combined with traditional PFR tools like flood barriers, self-closing airbricks, and non-return valves, can help to make a big difference in reducing floodwater ingress.

However, always seek advice from a property flood resilience professional to ensure the solutions are suitable for your home. If your property is older or listed, seek guidance from your local listed buildings officer. For more guidance on protecting historic properties, visit Historic England’s guide to flooding and historic buildings.

Copyright: Mary Long-Dhonau January 2025

This blog has been written for the RAIN project (Resilience and Innovation Northants) https://rainnorthants.co.uk/