A new damp patch after the work is worrying. Here is how to find the cause and what to fix first.
Cavity wall insulation is meant to make a home warmer and cheaper to heat. So a new damp patch on an outside wall some weeks or months after the work is alarming. Before you blame the insulation, work out which kind of damp you have. This guide climbs a ladder from free checks to the point where a specialist should look.
Damp after cavity wall insulation is usually either pre-existing water getting in that now shows, or condensation on a surface that has changed. The Centre for Sustainable Energy says damp directly caused by the insulation is very rare. Photograph the damp, check the gutters and brickwork outside, contact your installer about the guarantee, and treat any wet wall before reaching for a dehumidifier.
The Centre for Sustainable Energy (CSE) says cavity fill should not go into a home with signs of rising or penetrating damp, cracks, rubble or dirt in the cavity, blocked or overflowing gutters or heavy exposure to driving rain. The CSE adds that where water does get in, it is usually down to construction defects rather than poor installation, and a proper assessment before the work should spot them.
The Property Care Association (PCA) lists the usual sources of penetrating damp: blocked gutters and defective downpipes, worn mortar and brickwork, and faulty flashing. Condensation is a separate problem. GOV.UK describes it as moisture from cooking, showers and drying laundry cooling on colder surfaces such as window frames, corners and the low points of walls behind sofas or wardrobes.
Walk round on a wet day, from the ground. Look for overflowing gutters, dripping joints, downpipes that spill against the wall, cracked or crumbling pointing and lifted flashing. The PCA recommends regular inspection, cleaning and repair of these items. Clearing a blocked gutter is a small job, but do not use a ladder unless you are confident, and hire a tradesperson for anything high.
If the damp is wet, rain-linked or spreading, contact your installer first. The CSE says registered installers should be members of a body such as the National Insulation Association, CIGA or the British Board of Agrément, and CIGA provides a 25-year guarantee for faulty or inappropriate installation. If you are unsure whether your guarantee is still in place, you can ask CIGA, and the CSE offers free advice. For independent diagnosis, the PCA points to specialist surveyors,. Where mould has formed, clean hard surfaces with a mould and mildew product while wearing gloves, a mask and goggles, as GOV.UK advises. Cleaning alone will not stop it coming back.
A dehumidifier does nothing about rain getting into a wall or a failed installation, so fix those first. Once the wall is dry and the damp is clearly condensation, reducing indoor moisture can help. A loft-mounted Dryzen system covers up to 150 m2 per unit and extracts up to 12 litres a day for about GBP 20 a year in energy. Holding humidity around 50-55% helps stop the conditions mould and dust mites need. It needs a loft, it is for owner-occupied homes (not rentals unless the landlord authorises the changes), and the insulated ductwork only serves the central area or stairway.
Homes across the Medway Towns range from older solid-brick terraces to later estates, and cavity fill only applies to a home that has a cavity, so confirm your wall type from your installer paperwork or a survey before assuming it. See our pages for Walderslade, Rainham and Lordswood.
Not inevitably. The Centre for Sustainable Energy says directly caused damp is very rare across the roughly four million UK homes that have had the work, and that where water gets in it is usually down to construction defects rather than the installation.
Start with your installer and the paperwork they gave you. CIGA provides a 25-year guarantee on cavity wall insulation fitted by registered installers, covering problems caused by faulty or inappropriate installation, and has a route for reporting a concern.
Often, yes. Water getting in tends to follow the rain and sit near the fault, such as under a gutter joint or by a window. Condensation follows the cold, appearing in corners and behind furniture in winter. If unsure, ask a Property Care Association surveyor.
Only if the cause is condensation. It does not stop water entering a wall, and it is not suitable for rented homes unless the landlord authorises the changes or for homes without a loft.
Sources: Centre for Sustainable Energy: Cavity wall insulation; CIGA; Property Care Association: Penetrating damp; GOV.UK: Understanding and addressing the health risks of damp and mould in the home. General information, not a survey of your home.
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