To determine if your cavity wall insulation is faulty, you should look for several common signs or conduct specific checks. Faulty cavity wall insulation can lead to energy inefficiency, damp problems, and even structural damage.

Here are some indicators and steps to help you figure out if your insulation is not functioning properly:

1. Increased Energy Bills Sign of poor insulation: If your heating or cooling bills have significantly increased, it could be a sign that the insulation is no longer effective. Faulty or degraded insulation allows heat to escape in winter or lets in heat during summer, making your HVAC system work harder.
2. Cold Spots or Uneven Temperatures Inconsistent indoor temperatures: If you notice cold spots on the walls during winter or hot areas during summer, it could be a sign that the insulation is not properly distributed or has become damaged.
   Touch test: You can press against the interior walls during cold weather. If the walls feel unusually cold, there might be an issue with the insulation.
3. Dampness or Moisture in the Walls Condensation: Dampness on the walls, especially near the base of the wall or at window frames, can indicate that moisture is getting into the cavity. This could be caused by damaged insulation or gaps in the cavity wall.
   Mold or mildew: The presence of mold or mildew on the walls inside the house could be a sign that moisture is trapped in the insulation or the cavity, which might have been compromised.
4. Visible Damage to the Exterior Wall Cracks or holes: Visible cracks in the exterior wall may allow water to enter the cavity, causing the insulation to get wet. If the mortar or brickwork has deteriorated over time, it may have impacted the insulation as well.
   Efflorescence: White powdery stains on the exterior of the wall can indicate moisture infiltration, which may be damaging the insulation inside the cavity.
5. Pest Infestation Rodent or insect problems: Insulation materials, especially older ones, can attract pests such as rodents or insects. If you notice signs of rodents in your attic or walls, they might be living in or feeding on the insulation material.
   Pest-related damage: If you hear rustling or see nests inside the cavity, the insulation may need to be removed and replaced.
6. Water Damage or Staining Inside Damp patches on the interior wall: If you notice damp patches or water stains on the internal walls, particularly in colder weather, it may be a sign of moisture infiltration in the cavity due to compromised insulation.
   Peeling wallpaper or paint: This can also be a result of moisture getting into the cavity and affecting the wall, especially if the insulation has become wet and is no longer providing a moisture barrier.
7. Poorly Installed or Settled Insulation Gaps in insulation: If the insulation was poorly installed, there may be areas where it has shifted or settled, leading to gaps. This will decrease its effectiveness and could lead to heat loss or moisture buildup.
   Uneven coverage: If your insulation is blown-in or loose-fill, it may have settled unevenly over time, leaving parts of the cavity exposed. This will also reduce its overall performance.
8. Unpleasant Odors Musty smells: A musty or damp smell in the house could be an indicator of moisture trapped in the insulation or the walls. This is often a result of poor ventilation, leaking insulation, or mold growth.
9. Signs of Mold or Damp in Attic or Loft Look in the attic or roof space: Inspect your attic or loft for signs of moisture or mold. Wet insulation can lead to long-term damage to timber and structural elements in the attic.
   Mold on roof timbers: If the insulation has absorbed moisture, it can lead to mold growth on roof timbers, rafters, or ceiling joists, affecting both the insulation and the structural integrity.
10. Professionally Conducted Testing Thermal imaging: A professional can use infrared cameras to scan your walls and identify areas where heat is escaping, which indicates gaps or problems in the insulation.
    Moisture meter: Professionals may use moisture meters to check if the insulation is wet or damp, which would indicate the need for extraction.
    Cavity wall inspection: A cavity wall inspection involves checking the wall’s condition, insulation type, and any moisture buildup. This can help confirm whether the insulation needs to be replaced or extracted.
11. Check the Age and Type of Insulation Old insulation: If your home has been insulated for many years, the material may have degraded or settled. Some older insulation materials, such as cellulose or wool, can compress over time and lose their effectiveness.
    Improper insulation material: If the insulation was improperly installed or made from outdated materials, it may be faulty. For example, some insulation materials are more prone to absorbing moisture than others.

What to Do If You Suspect Faulty Insulation:

Contact a professional: If you notice any of the signs above, it’s a good idea to contact a professional insulation contractor or a building surveyor. They can conduct an inspection and determine if your insulation needs to be replaced or extracted.
Cavity wall extraction: If your insulation is found to be damaged, wet, or ineffective, it may need to be removed (extracted) and replaced with new insulation.

Regular maintenance and timely checks are key to ensuring your cavity wall insulation is performing as expected and preventing potential issues from worsening.