Cavity wall insulation is supposed to lower heating bills and save us money but for many, it’s become a nightmare. Damp walls, cold spots, mould, condensation and damaged plaster are just a few of the issues that can arise when this insulation is incorrectly installed.

On this page we’ll look at:

• How much it costs per square metre to remove cavity wall insulation.
• Example prices for terraced, semi-detached and detached homes.
• Additional costs to consider.
• How cavity wall insulation is removed.
• How long the work takes.
• Why cavity wall insulation fails.
• What can happen if you don’t remove faulty cavity wall insulation.

Cavity Wall Insulation Removal Prices

The table below displays prices for the removal of cavity wall insulation per square metre of wall and also separate guide prices for typical homes of various sizes:

Additional Costs to Consider

The prices on this page are for cavity wall insulation removal and the making good of any holes drilled or bricks removed during the removal process. the prices do not include:

• Making good or replacing internal plaster or plasterboard that’s damaged, wet or mouldy etc.
• Re-rendering the exterior wall.
• Replacing rusted or failed wall ties.
• Scaffold costs should it be needed to access hard-to-reach parts of the home.
• Redecorating internal or external walls.

These additional costs can be considerable but many may not apply to your home.

As a general rule of thumb, the longer you leave wet insulation in the cavity, the more damage it will cause to the plaster, paint, wallpaper and wall ties.

How Cavity Wall Insulation is Removed

There are 7 steps to removing cavity wall insulation:

1. Drill a test hole and remove a small amount of insulation for inspection.
2. Supply the customer with a written quotation for the removal project.
3. Drill holes into the wall for the air pump.
4. Drill large holes or remove bricks for the extraction pipe.
5. Remove and dispose of the insulation.
6. Inspect the cavity wall and record with a camera.
7. Repair the exterior wall. Fill holes and reset bricks etc.

The specialist may decide that vent bricks should be installed at specific points along the wall to help the cavity dry out. If they’re required and how many are needed will depend on how wet the walls are.

Put simply, holes are drilled or bricks removed at strategic places along the exterior wall. A pump pushes air into one hole while a powerful hoover sucks out the material from the other hole. This process is repeated across all the walls of the home until all the material is removed. The cavity is then inspected with a camera before the bricks are reset and any holes filled and made good.

How Long Cavity Wall Insulation Removal Takes

How long cavity wall insulation removal takes will depend on:

• The type of insulation installed.
• How wet the insulation is.
• How easy or difficult the walls are to access.
• The materials used in the construction of the exterior walls.

A typical 3-bed semi-detached home can be completed in 1 to 3 days with most taking around a day and a half.

Why Cavity Wall Insulation Fails and Needs to be Removed

Cavity wall insulation is an infill material that is pumped into the void between the outer and inner walls of a home, it’s designed to trap heat in the home and reduce heating bills.

Over 99% of installations are trouble-free but for some, failures may occur due to:

Poor Quality Brickwork

If the brickwork or other material on the exterior of your walls is in poor condition, rainwater can pass through into the void and soak the insulation. The damp insulation then transfers the moisture to the inner wall where mould, condensation and other problems become apparent. Because the insulation is absorbant and the cavity wall is sealed with no airflow, the walls may never dry out, even if the exterior wall is repaired. Every installer should thoroughly check the condition of the exterior walls before filling the cavity with insulation, but many don’t and the industry is full of salespeople working on commission.

Leaking Concrete Gutters and Wet Cavity Wall Insulation

Concrete gutters were popular immediately after the second world war as other materials such as cast iron became expensive. Cheap concrete blocks were joined together and designed to catch rainwater from the roof. Unfortunately, these blocks are extremely heavy and are prone to movement which causes cracks and leaks directly above the cavity wall insulation. Every installer should check that any home with these concrete blocks has had them lined with rubber so they won’t leak onto the absorbent cavity wall insulation material. Unfortunately, some installers don’t check the gutters and just install the insulation.

Sagging Insulation

Some types of insulation will sag over time and this creates voids where the wall isn’t properly insulated. This leads to cold spots where condensation may appear. Wet insulation is heavier than dry insulation so is more likely to sag. The best insulation is arguably polystyrene balls as they won’t sag and don’t absorb moisture.

You Live in an Exposed Area (Zone 4)

Some areas of the UK experience considerable wind-driven rain and due to the risk of water penetrating the walls and soaking the insulation, this type of insulation shouldn’t be fitted or should only be installed if the wall is 100% sound and waterproof.

Looking at the chart below, if you live in zone 4 or some areas within zone 3, you are at a higher risk of experiencing problems with cavity wall insulation:

Some installers will fit cavity wall insulation without any regard to the wind-driven rain the property may be subjected to.

Damaged/Rusted Wall Ties

The inner and out walls of most homes are held together with ties – pieces of metal that prevent the walls from separating. If the cavity wall insulation becomes wet, these ties can rust and fail and the walls can become dangerously unstable. If you suspect your cavity wall insulation is wet, it should be removed promptly so the ties don’t rust and fail.

What Can Happen if Cavity Wall Insulation Fails and Isn’t Removed

If your cavity wall insulation is wet, it’s unlikely to dry out on its own, so time is of the essence and it should be removed promptly.

If wet insulation is left in the cavity you can expect:

• The plaster and plasterboard to become so damaged from damp and mould that they will need to be replaced.
• Rusted or failed wall ties may need to be replaced.
• Wallpaper and paint may peel and extensive redecoration may be required.
• Clothes, bedding, carpets and furnishings may become mouldy and damaged.
• Occupants may experience breathing difficulties (coughs, chest pain etc) due to the excess moisture in the home.

The Best Cavity Wall Insulation Material

Every material has the potential to fail and transfer moisture to the inner wall but in general, polystyrene balls are the best choice as they:

• Aren’t absorbent.
• Have small gaps around them so any water that does enter the cavity drops down to the ground rather than moving sideways to the inner wall.

Regardless of which material is used in the cavity, the outer wall should be 100% waterproof and sealed, especially if you live in an area prone to wind-driven rain.

Does Every Home Need Cavity Wall Insulation?

There are plenty of homes in the UK that do not have any cavity wall insulation fitted and while they may not be so thermally efficient there are other ways to reduce heating bills:

• Topup the loft insulation.
• Replace the windows with double or even triple glazing windows.
• Upgrade the boiler to a more efficient one.
• Powerflush the radiators to improve efficiency.

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