• Wet Insulation: The Do’s & Don’ts

    | by Dave Ashbolt

    Have you ever wondered, “What happens when insulation gets wet?”. It’s a question homeowners and construction enthusiasts often ponder, and with good reason. Insulation plays a crucial role in maintaining comfort and energy efficiency in your home or building. However, it is not impervious to moisture, and when insulation does get wet, it can lead to a series of issues that affect both your property and your wallet.

    In this easy-to-follow guide, we’ll take a look at different insulation types and how they might attract or retain moisture. Plus, we’ll share some practical tips for dealing with damp insulation should it ever happen.

    By the end of this guide, you’ll have a solid grasp of how to keep your construction projects moisture-free when it comes to insulation.

    The Impact of Wet Insulation

    Wet insulation is a serious issue that can cause a wide range of problems in your home if not taken care of right away.

    Wet insulation can have a significant impact on a building’s performance and thus the comfort and wellbeing of its occupants, since it compromises the thermal efficiency, structural integrity, and indoor air quality of a structure.

    If you don’t replace or dry out wet insulation quickly, you run the risk of mould growth in the area where the dampness has occurred. Not only is mould unsightly and smelly, it can also trigger allergic reactions in some people who are sensitive to mould spores. Additionally, mould can cause structural damage over time if left untreated, due to its ability to eat away at organic materials like wood.

    On top of this, water-damaged insulation tends to become less effective at regulating temperature within the home. This means that even if you manage to dry out the affected area quickly before any structural damage occurs or mould starts to grow, you may still find yourself with higher energy bills because your house has become less efficient at regulating temperature than before the incident occurred

    What Can Cause Insulation To Become Wet?

    Insulation can attract and retain moisture due to a range of factors, and each factor contributes to the problem in its own way. Here’s a more in-depth exploration of what can cause insulation to retain moisture:

    Inadequate Ventilation: Poor ventilation within a building can be a significant contributor to moisture retention in insulation. When there isn’t enough airflow to carry away moisture, it can become trapped in the enclosed spaces, including within the insulation material. This is particularly common in areas like attics and crawl spaces that may lack proper ventilation systems.

    Water Intrusion: The most obvious cause of moisture retention in insulation is water intrusion. Leaky roofs, damaged siding, plumbing leaks, or foundation issues can allow water to penetrate the building envelope. When this happens, insulation can absorb the water, reducing its effectiveness and potentially leading to mould growth and structural damage.

    Condensation: Condensation occurs when warm, moist air comes into contact with a cold surface, causing the moisture in the air to convert into liquid form.

    Insulation located in areas with temperature differentials, such as between the interior and exterior of a wall or ceiling, can become a condensation point. This condensed moisture can saturate the insulation over time.

    High Humidity: Regions with high humidity levels can also contribute to moisture retention in insulation.
    Air itself can contain moisture. This can pass through and settle within the insulation. 

    Poor Installation: Incorrect installation of insulation can lead to gaps, seams, and compression of the material, creating pockets where moisture can accumulate. Additionally, improperly sealed vapour barriers or vapour retarders can allow moisture to penetrate the insulation.

    Types of Insulation and their Susceptibility to Water Damage

    Certain types of insulation are more effective at dealing with damp conditions than others. 

    Spray foam insulation stands out for its exceptional water resistance, making it a top choice for protecting against moisture damage. This specialist-applied insulation not only prevents mould but also boosts energy efficiency by sealing air leaks. Due to its complex application process, it’s a task strictly for trained professionals, ensuring optimal performance and safety.

    For novices and DIYers, closed-cell foam insulation and rock mineral wool insulation are the best moisture resistant options available on the market. They will keep your home well insulated and dry, no matter what the weather throws at them.

    Examples of water-resistant insulation solutions include:  

    • Rockwool insulation is water-repellent due to the resin bond it’s covered in. Rockwool insulation is moisture resistant and vapour permeable. Engineered to repel water, water will drain away rather than soak into the insulation, while gaseous water vapour will simply pass through it. Rockwool manufactures a range of acoustic insulation slabs, such as RWA45 and Flexi Slabs.
    • Insulation boards tend to have good moisture resistant and water repellent qualities. Products such as Celotex and EcoTherm boards for instance have aluminium foil facings on both sides, and a PIR foam that is resistant to water.

    On the other hand, materials such as wood fibre insulation is not so effective: wood is highly susceptible to moisture saturation and warping, both of which can compromise surrounding structures.

    Similarly, loose fill insulation (such as fibreglass and cellulose insulation) is another material that temporarily loses its thermal resistance in the presence of moisture. Should fibreglass absorb water, the water droplets will infiltrate the air spaces between the fine glass fibres, greatly reducing the material’s insulant properties.

    What To Do If Insulation Does Get Wet?

    When insulation becomes wet, it necessitates a careful and methodical approach to mitigate potential issues and restore its functionality. 

    1. Identification of The Moisture Source

    Whether it’s a leaking roof, burst pipe, or any other source, addressing the issue promptly is crucial to preventing further moisture ingress and accumulation (in the insulation).

    2. Safety Precautions

    Before proceeding with any actions, safety precautions must be taken. The turning off of all electrical systems in the affected area is necessary to minimise the risk of electrical hazards.

    3. Assessment of Damage

    A comprehensive assessment of the extent of moisture damage in the insulation is essential. Depending on the severity of the moisture exposure, insulation may need to be partially or entirely replaced. The evaluation should also include checking for any signs of mould or mildew growth, which may require professional remediation.

    4. Removal of Wet Insulation

    When insulation material has absorbed a substantial amount of moisture, its removal becomes imperative. This task should only be undertaken by qualified professionals who wear the necessary protective gear to safeguard against potential contaminants or mould spores.

    Moisture-saturated insulation not only loses its effectiveness but can also become a breeding ground for harmful microorganisms. The removal process should be executed meticulously to prevent any cross-contamination or health risks.

    5. Drying the Affected Area

    After removing wet insulation, the next critical step is to thoroughly dry the affected area. Proper drying helps prevent mould growth, structural damage, and ensures the new insulation’s effectiveness.

    Industrial-grade dehumidifiers and fans can be employed to expedite the drying process. Adequate ventilation should also be maintained during this phase to prevent the recurrence of moisture issues.

    6. Insulation Repair or Replacement

    Whether to repair or replace insulation depends on several factors, including material type, the extent of moisture damage, the presence of mould, energy efficiency concerns, and the age of the insulation. 

    A professional inspection can provide a thorough assessment, helping you make informed decisions about repair or replacement.

    7. Addressing Mould and Mildew

    Should you spot mould during inspection, consulting with mould remediation specialists is necessary to ensure the safe and effective removal of any microbial growth.

    When dealing with wet insulation in a closed wall cavity, we advise that you remove the wet cavity wall insulation and allow the cavity to fully dry out before attempting the installation of new materials.

    Insulation Moisture Prevention – Prevention Is Better Than Cure

    As outlined, the best way to prevent wet insulation is to ensure that proper sealing and insulation against moisture are in place in your home before installing new insulation.

    This includes checking for holes, gaps, and cracks around windows, doors, vents, and pipes. Sealing these points with caulk or weather-stripping materials will help keep out any excess moisture from entering your home’s walls and attic spaces.

    By taking precautionary steps, such as sealing up any potential entry points for excess moisture and using products designed specifically for damp conditions, you can reduce the risk of moisture infiltrating existing or newly installed insulation

    We also recommend that you: 

    – Make sure your roof and gutters are in good condition and are properly draining

    – Keep your home well ventilated, especially in the attic

    – Add technical insulation around pipes and other objects that could cause water damage

    – Use a water repellent insulation, like spray foam or closed-cell foam insulation

    – Cover your insulation with a moisture barrier, like plastic sheeting


    There’s no denying that wet insulation is bad news for homeowners. It increases energy costs by making homes less efficient at regulating temperatures. It also creates an environment where mould growth is more likely to occur. This can potentially cause health problems as well as long-term structural damage in some cases.

    It’s important therefore that homeowners take steps to ensure their insulation stays dry. This will help to protect their properties and avoid costly repairs down the line. 

  • All Categories