Penetrating Damp

What is Penetrating Damp?

The term refers to moisture that enters a building through the roof or external walls, which can penetrate the interior and cause considerable damage to plaster, timber and other materials. The wet climate we experience here in the UK presents the perfect environment in which damp and mould can thrive and with record rainfall figures in 2025, all buildings in the capital are under threat. Damp travels through building materials with capillary action, just like paper soaks up liquid and unless you are observant, you could miss the tell-tale signs and that could cost a lot in repairs.

Tell-Tale Signs of Penetrating Damp

Penetrating damp can be recognised by the following signs:

• • Persistent damp patches that do not dry out
  • Musty smell in the house
  • Soft & discolored timber
  • Blown plaster
  • Salt stains on walls and ceilings
  • Mould forming on interior walls and timber lengths
  • Moss growing on external walls

  If you notice any of these signs, it is time to contact London Damp Specialists and arrange for one of our accredited damp surveyors to inspect the building. We offer several levels of independent damp survey, depending on your needs and you receive a thorough written report, complete with images, the day after the survey has been completed.

  What Causes Penetrating Damp?

  Penetrating damp can be caused by the following:

  • Leaking roof – It might be a few missing roof tiles that were lifted by gale-force winds, or blocked guttering that causes rainwater to run down external walls, which leads to serious damage in the loft; damaged rafters and joists, which might need to be replaced. Regular roof inspections are a good idea, as they give you an early warning when damp attacks the internal roof structure.
  • Compromised external walls – Years of driving rain can lead to crumbling render and masonry and until this has been addressed, damp will continue to impact a structure. Mortar is easily damaged by continuous rain and walls might need to be repointed to resolve the issue. Regular inspections are advised and any issues should be promptly resolved.
  • Defective door and window sealant – Most window and door frames are sealed with mastic and if the seal is broken, water can penetrate into the interior. You should inspect all timber frames, specifically looking for breaks in the sealant and repair any breaches.
  • Leaking water pipes – Mains water is pressurised and leaks are a common occurrence and if not repaired, a leak can lead to serious damage. Check all walls and ceilings for tell-tale damp patches that persist and do not dry out.

  All of the above are common causes of penetrating damp and if your London home has damp issues, you need to book an independent damp survey in order to get to the root cause.

  Best Long-Term Treatment for Penetrating Damp

  Of course, it very much depends on the root cause of the problem. A leaking roof, for example, needs to be identified and promptly repaired before any damage repair is carried out; if damp is coming through the external walls, the same applies. Waterproof render is one solution that is commonly used to repair external walls.

  Repairing Water Leaks

  Pressurised water pipes frequently spring a leak and even a slight leak can cause significant damage to plaster and eventually, timber. It makes sense to periodically inspect all ceilings and walls, specifically looking for tell-tale damp patches. Of course, fixing a leak should be done before any damp damage is repaired.

  Damp Does Not Announce its Arrival

  There are no apparent signs when damp strikes, which means you should arrange for regular damp inspections as a form of early detection. If a homeowner is not observant, a damp issue in a spare room, for example, can lead to serious repairs.

  If you suspect that your London home is impacted by penetrating damp, book an independent damp survey from an established company and get to the root of the problem. We provide a detailed written report within 24 hours of the survey completion, plus we can make treatment recommendations and put you in touch with a leading damp-proofing company.