Problems with cavity wall insulation – what can go wrong

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  • Cavity wall insulation (CWI) is a great option to make your home more efficient and save on energy bills. Most installations go off without a hitch, leaving homeowners to reap the benefits of a warmer, more comfortable living environment. Problems with cavity wall insulation are cropping up, so we’re here to tell you why.

    “We have issued 6.2 million guarantees for cavity wall insulation and have a loss ratio of only 0.43%,” reassures Nigel Donohue, CEO of the Insulation Assurance Authority.

    Sometimes, however, things can go wrong. Most cavity wall problems are the result of installation and maintenance issues, which can be easily avoided with reliable pre-installation assessments and good installation practices.

    What are the most common cavity wall insulation problems?

    Image credit: Future plc/Simon Whitmore

    Here are some issues that can arise with CWI and what to do if you encounter them.

    1. Damp and moldy cavity wall insulation problems

    Properly installed, cavity wall insulation can reduce moisture and mold problems and make your home a more comfortable place. Problems can arise if the work is poorly done or if the house is unsuitable.

    Dampness and mold are usually easy to spot. Often the problem stems from poor condition walls that were not repaired before the cavity wall insulation was installed. Cracks in masonry or plaster, crumbling mortar and leaking gutters can all allow water to enter the cavity. This will soak the insulation, which means it won’t work as it should, eventually leading to problems.

    A good company will carry out a pre-installation survey and advise you on what needs to be done before the CWI is installed or advise you if cavity wall insulation is not appropriate. After installation, good general property maintenance, such as repointing mortar joints and regularly checking gutters, will help prevent future problems. Ventilation is also important to prevent moisture and mold.

    2. Inadequate ventilation

    Good air circulation is essential inside your home, to ensure it stays cool and free from problems such as mold. When you insulate a house, you make it more airtight. Installers should therefore ensure that the existing airflow is maintained and that additional ventilation is installed if necessary.

    “We install ventilation as standard as part of a CWI job,” says Ed Andrews, commercial director at InstaGroup. “But homeowners should be aware of what they can do to reduce the risk of humidity problems, such as opening windows and using extractor fans.”

    Ventilation problems can be exacerbated if cavity wall insulation is improperly installed or sags over time. As well as causing cold spots, it could also block vents, so proper specification and installation is essential.

    3. Badly filled cavity wall insulation

    When renovating insulation, obstructions in the cavity, such as bits of mortar, can snag materials such as mineral wool. If a cavity is too thin, the insulation may also not spread as expected.

    Using the right type of insulation for your home is the first step to avoiding this. Proper installation is also essential. A cowboy installer might not give the necessary care and attention to ensure that the entire wall is properly treated.

    Since the cavity is hidden, there is no easy way to spot this kind of problem. Sometimes you’ll spot cold spots, but you might not get wind of a problem until you’ve had several months of utility bills. The thing to look for is whether your energy consumption (rather than the price, which can fluctuate) hasn’t fallen as much as expected from the previous year.

    4. Unsightly renovation installations

    CWI is installed by drilling holes in the exterior wall and blowing or injecting the insulation into the cavity. Good contractors will do a decent job of fixing them, and the holes tend to fade with age; but bad cover-ups can be unattractive. In addition to talking to your installer about how they’ll hide their work, do your research and ask past customers if they’re satisfied with the insulation performance, final appearance, and after-sales service.

    Who should I contact in case of cavity wall insulation problems?

    yellow living room with french doors

    Image credit: Future plc/Simon Whitmore

    Talk to the original installer and ask them to assess the issues and perform corrective work. If they are unwilling to provide support or have gone out of business, your next option is to contact your warranty or warranty provider. If all else fails, appoint your own expert to do an independent assessment.

    Which houses are unsuitable for cavity wall insulation?

    Properties in locations that are exposed, subject to wind driven rain or without a moisture barrier layer may not be suitable for cavity wall insulation. “Some properties may also use particularly porous brickwork in the exterior construction or have a very narrow cavity which is not suitable for CWI,” says Matthew Evans, UK Technical Manager at Kingspan Insulation.

    In the worst case, unsuitable insulation may need to be removed – a process that can cost £1,000. That’s why it’s important to use a registered installer whose work will be covered by a 25-year CIGA warranty.

    If there are obstructions inside the cavity, water can seep through the insulation. Mortar snot (chunks) are the most common cause. This may mean that it is not possible to install CWI, so another solution (such as exterior wall insulation) may be your best bet for improving energy efficiency.

    Whether or not a home is suitable for cavity wall insulation should be determined by a pre-installation assessment by a reputable company. This should include inspection of the cavity using a probe camera.

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