Wet cavity wall insulation is a serious problem that typically requires extraction. Here's how insulation gets wet, what happens to it and what you should do.
In exposed locations or where external brickwork is permeable or damaged, driven rain penetrates the outer wall and soaks into the insulation. This is the most common cause in North East England.
Failed or eroded mortar joints in the outer leaf allow water to track into the cavity, bypassing the drainage gap that cavity construction was designed to provide.
Leaking or overflowing gutters deposit water directly onto the wall face, which can then saturate cavity insulation. Ground drainage issues near walls can also cause rising damp to interact with insulation.
Wet insulation doesn't dry out naturally while it remains in the cavity. The cavity environment — enclosed, with minimal airflow — means saturated insulation stays wet indefinitely. Extraction is almost always necessary once insulation has become significantly saturated.
Wet insulation conducts heat instead of retaining it. A saturated cavity actually performs worse than an empty one — your home becomes harder and more expensive to heat.
Moisture bridges from the outer to the inner leaf through the saturated insulation. This appears as damp patches, tide marks and discolouration on internal walls — typically worse after rain.
Persistent damp in walls creates ideal conditions for black mould — on internal surfaces, behind furniture and inside the wall cavity itself. Mould poses significant health risks, particularly for respiratory conditions.
Mineral wool that stays wet for extended periods breaks down, compacts and may develop bacterial or fungal contamination. Once this happens, the material cannot recover its original performance even if it dries out.
Camera inspection confirms whether the insulation is wet, how extensive the saturation is, and what type of insulation is present. This informs the extraction plan.
Before or alongside extraction, identify and fix the source of water entry — damaged brickwork, failed pointing, guttering issues. Extracting and re-insulating without fixing the source will result in the same problem recurring.
Once the source is addressed, the wet insulation is extracted and the cavity allowed to dry thoroughly before any further decisions about re-insulation.
Don't wait to act. The longer wet insulation remains in the cavity, the greater the damage to internal walls, decoration and potentially structural elements. Mould established in a cavity is also difficult to fully address without extraction.
Zest can inspect the cavity and advise whether extraction is needed.
