Cavity Wall Insulation Problems: Signs, Damp & What To Do

How I know cavity wall insulation has failed

From a customer's perspective, the most obvious signs are damp patches appearing on internal walls, brickwork outside where the face has started to fail and spall, and a property that just starts to feel colder over time. These are all indicators that something has gone wrong inside the cavity.

When I inspect, I drill into the cavity at two to three points on each elevation - you cannot rely on a single inspection hole to understand the full picture. What I am looking for is droplets of moisture sitting on mineral wool, slumped insulation that has compacted and left gaps, urea formaldehyde that crumbles when you touch it rather than springing back, or blown beads that fall out or have obvious voids where coverage is incomplete.

Why it fails

Cavity wall insulation only became standard around the mid-1990s. Anything pre-1990s, if it has not been retrofitted, you can assume the cavity is either empty or was filled using older methods and materials that have since degraded.

The common causes are not dramatic. They are things like mortar droppings in the cavity creating a bridge for moisture to cross from outside to inside. Or the damp proof course being breached because ground levels have been built up over time with new driveways, pathways, or planting beds. You should have around 150mm of clearance below the DPC - roughly two bricks. If that has been reduced to 30 or 40mm, rainwater can splash up into the cavity and soak the insulation.

You cannot just take the insulation out and chuck new insulation in. There has to be a process in between.

What extraction and refill actually involves

Once the failed insulation has been extracted, there is a pre-fill inspection of the cavities. I check for blockages - rubble, leftover insulation, mortar droppings - anything that could create a path for water.

I check the damp proof course to make sure it is intact and has not been breached or bridged by raised ground levels. I check the condition of wall ties, because if the insulation has been wet for a long time, that moisture puts strain on the ties and they may have started to corrode. If wall ties need replacing, that can be done at the same time.

These are all solvable problems. But the point is that extraction and refill is not a one-step process. Every one of these checks needs to happen before new insulation goes in, or you are just setting up the same problem again.

What to do next

If you suspect your cavity wall insulation has failed, or you are seeing damp, cold spots, or spoiling brickwork, book a free call to talk through your situation. We can help you work out the right next step and what your options are.