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Cavity wall insulation problems: what to do if CWI fails

Damage to the cavity wall insulation caused by penetrating damp

Cavity wall insulation (CWI) can be an effective and efficient means of improving your home’s thermal efficiency. But it can go wrong. The short-lived UK Government Green Deal initiative sparked a mini-explosion of contractors offering cavity wall insulation. After double/triple glazing, cavity wall insulation is one of the most popular energy-efficiency investments with a big energy saving impact if installed correctly. Read on to find out how to fix cavity wall insulation problems.

Have you noticed an increase in damp and mould after CWI installation? It’s important to know that you haven’t made a mistake in getting your home retrofitted with insulation. You may have been let down by professionals who undertook the work before the PAS 2030 regulations came into force, requiring the appointment of a retrofit coordinator to oversee installation. Perhaps they simply did not install the insulation properly.

  • How do you know if your cavity wall insulation has failed?
    Cold and wet patches on internal walls could be signs of failed CWI. Water-damaged and blistered plaster, wallpaper or painted surfaces are also warning signs. On the external wall, look out for spalled or cracked brickwork.

  • Can damp come through a cavity wall?
    Yes, this is a common problem with cavity wall insulation. Wind-driven rain can seep through unprotected brick walls. It bridges across the insulation, brick ties and obstructions in the cavity. The result? Internal dampness!

  • Is it best to remove cavity wall insulation?
    In most cases, no. If the cavity wall insulation has been adequately filled throughout the cavity, it needs to dry out. Stormdry Masonry Protection Cream allows CWI to dry out and return to its original heat efficiency power.

  • How do you stop damp in a cavity wall?
    Stormdry Masonry Protection Cream is the best way to ensure penetrating damp doesn’t ruin CWI. It allows wet insulation to dry out and stops further moisture damage.

Failed cavity wall insulation warning signs: what to look out for

If you know your home has CWI installed and have noticed any of these symptoms, your cavity wall insulation may have failed.

  • Damp patches on the wall

    Failed cavity wall insulation dampness usually presents as random spots of wetness on the wall.
  • Damaged external brickwork

    Bricks are naturally porous. Spalled or cracked brick can absorb wind-driven rain to introduce moisture into the cavity wall.
  • Blistered or blown plaster or wallpaper

    Waterlogged plaster or wallpaper is a telltale sign of a damp problem. Look for damp patches and blisters of moisture anywhere on the wall.

What to do if your cavity wall insulation fails?

If you suspect that damp problems in your home stem from failed cavity wall insulation, speak to your original installer to assess and correct the problem. Cavity wall insulation providers in the UK are legally required to issue 25-year guarantees. These are usually backed by CIGA (Cavity Insulation Guarantee Agency). If your original provider cannot or will not deal with the problem, contact CIGA or your guarantee issuer for the next steps. 

In some cases, remedial works can be done to alleviate the dampness and allow damp cavity wall insulation to dry out and remain in place to perform as it should.

Failed Cavity Wall Insulation masonry repair and protection guide

Cavity Wall Insulation under a Microscope

If your cavity wall insulation has failed as a result of damaged brickwork, there are a couple of things you can do to protect it from further damage. Heal your home from the effects of damp cavity wall insulation with this 3-step guide. 

  1. Repoint and bridge cracks in brickwork
  2. Protect cavity wall insulation and cavity walls from moisture ingress
  3. Replaster with a damp-resistant plaster system

The goal here is to stop moisture ingress. Bricks are naturally porous – find out more about bricks and penetrating damp here – which means they naturally absorb moisture around them. First, ensure your exterior walls are in good condition. Pay special attention to weather-facing walls, as they will take the brunt of rainy conditions.

Repoint and bridge cracks in brickwork

Stormdry XR Mortar Finish

Ensuring that moisture cannot easily get into your house through external walls is an important part of fixing a house with failed cavity wall insulation. 

Repointing damaged mortar joints is a relatively simple process.

Stormdry XR-Mortar is a water-resistant repair mortar specially developed for damaged pointing and to seal cracks in brickwork. Its malleable formula prevents cracking. Easy to apply with a cartridge gun.

Protect cavity wall insulation and external walls from moisture ingress

Stormdry Masonry Protection Cream is a breathable waterproofing brick cream. It can be safely applied to walls with damp cavity wall insulation to dry them out. Stormdry Cream stops rain and water from entering brickwork while letting water vapour pass through. Affected cavity wall insulation can comfortably dry out while being protected from getting any wetter.

Replaster with Dryzone Express Replastering System or Renovation Plasters

Unfortunately, damp plaster must be replaced. Some plasters retain moisture, causing the finish to blister and crumble. Damp plaster is weak and difficult to apply finishes like paint and wallpaper over. The dampness will transfer to the paint or wallpaper to ruin that too.

Once the root cause of the cavity wall insulation failure has been dealt with, you must remove all damp plaster and replaster. Whether you choose plaster or plasterboard, Dryzone has options for complete damp resistance.

How does cavity wall insulation fail?

Cavity walls are usually filled with one of 4 types of insulation:

  • Injected Polyurethane Open or Closed Cell Spray Foam
  • Expanding Polystyrene Insulation Beads
  • Blown Mineral Wool Insulation
  • Blown Mineral Wool Insulation

Cavity wall insulation is unsuitable for buildings with damaged brick walls, uncapped cavities, or exposed areas that experience high levels of wind-driven rain without an appropriate breathable brick waterproofing treatment. Cavities under 50mm wide are not suitable for CWI at all, although most modern homes have 50-100m cavities. Whether you install full-fill or partial-fill insulation is dependent on the cavity size. A suitable retrofit coordinator must be appointed to assess and decide on the suitable insulation measure. Generally, partial-fill insulation carries more risks than full-fill insulation, although again this is dependent on cavity width.

Whenever something goes wrong, it’s important to go back to the beginning of the process to understand exactly what has happened. In line with PAS 2035 retrofit installation regulations (webinar link), you should always engage a TrustMark-approved retrofit coordinator

Prior to CWI installation, the condition of brick walls must be carefully assessed. Damaged pointing and spalled or cracked bricks must always be fully repaired before CWI installation. The state of the cavity itself must also be assessed. 

If appropriate precautions were taken and you are experiencing problems, something may have gone wrong in the installation process.

Why CWI installation goes wrong

House insulation by injecting microbead pearls in the cavity walls

Spray foam, polystyrene or mineral wool installation involves drilling a hole and injecting it inside, where it expands and solidifies. Because you can’t see exactly where the foam is settling, total coverage is often assumed. Day-to-day condensation in the home can create cold spots in the cavity where the wall insulation did not reach. 

A common cold spot appears on mortar-covered wall ties (sometimes called ‘snots’ in the construction industry) that bridge the internal and external walls.

Rubble and mortar are often left inside cavity walls during the construction process. If there is debris present in the cavity, it absorbs and retains moisture that penetrates the external wall.

Cavity walls should be sealed at the top. In cases where the cavity is left open, moisture can condense into the loft to cause dampness and mould issues.

Sometimes other measures like trickle vents for windows should be installed prior to installation to compensate for increased thermal efficiency. Failure to do so may result in increased humidity levels and associated condensation.

Cavity trays must be installed in between the internal and external leaves to allow moisture to drain away from the structure. Insulation must also be consistent throughout without air gaps. Doing so will help avoid heat loss, condensation and associated dampness.

When moisture reaches the internal wall, it causes dampness and mould growth on the internal walls. To make matters worse, the insulation itself is saturated with moisture. Moisture-saturated materials are poor insulators. Wet insulation is less efficient at retaining heat than dry insulation.

The installation itself can also go wrong. CWI installation is a highly technical retrofitting procedure that should only be carried out by fully qualified professionals. Foam injection insulation is a complex operation that requires careful consideration and scientific know-how to ensure the foam properly expands and adheres to the wall cavity. Air gaps present in the insulated cavity can cause cold spots that attract moisture and condensation, compromising the entire installation.

Cavity wall insulation removal

In cases where the installation itself was faulty and the wall is not correctly insulated, a professional contractor must be engaged to remove the cavity wall insulation and reinstall it correctly. Stormdry Masonry Protection Cream allows damp CWI to dry out and stops penetrating damp from affecting the insulation in future. While Stormdry will improve the energy efficiency of your home, if CWI is not correctly installed, you will not get the best out of it.

For the best advice on how to best treat your damaged CWI, contact our technical team.

For more information call
01403 210204