Top Five Common Defects Identified in Diagnosis Reports
23 April 2026If you have spotted an issue in your property like damp patches or cracking, a Defect Diagnosis Report is designed to identify the cause and recommend the right solution.
In London properties, particularly older buildings, certain defects appear more frequently than others. Understanding these issues earlier can prevent more extensive damage and unnecessary cost.
These are five of the most common defects we identify through our thorough inspections.
Japanese Knotweed
Japanese Knotweed is one of the most serious issues a property can face. It is an invasive plant that can grow rapidly and cause structural damage by exploiting weaknesses in buildings, drains, and boundary walls.
- It can grow through cracks in concrete, brickwork, and paving
- It is difficult and costly to remove
- It can even affect property value and mortgageability
Mortgage lenders often require evidence of a professional management plan before proceeding, so early identification is essential to prevent spread and reduce long-term costs.
Wet Rot
Wet rot is a timber decay caused by prolonged exposure to moisture. It typically occurs where timber has been allowed to remain damp over time, often due to leaks or poor ventilation. It is not reversible.
Common signs include:
- Soft or spongy timber
- Darkened or cracked wood
- A damp or musty smell you can’t get rid of
Wet rot is usually localised to the affected area, but if left untreated it can compromise structural elements such as floor joists or roof timbers. Addressing the source of moisture is the first and most important step.
Dry Rot
Dry rot is a more serious form of timber decay caused by a specific fungus that can spread through a building if conditions allow. It can travel through masonry to reach new timber to cause extensive structural damage, and often remains hidden until significant deterioration has occurred.
Signs of dry rot include:
- Cracking or shrinking timber
- A brittle, cube-like appearance in wood
- Fungal growth or a distinctive mushroom-like smell
Unlike wet rot, dry rot can spread beyond the original source of moisture, making early detection and specialist treatment critical.
Rising Damp
Rising damp comes about when moisture from the ground travels upwards through walls by capillary action. Though it is often discussed, it is also frequently misdiagnosed, which makes professional assessment particularly important.
Typical indicators include:
- Tide marks on internal walls
- Peeling paint or wallpaper
- Salt deposits on plaster
Older London properties may not have an effective damp proof course, or it may have simply deteriorated over time. Correct diagnosis is vital, as inappropriate treatments can be ineffective and rather costly.
Condensation
Condensation is one of the most common causes of damp in modern homes. It occurs when warm, moisture-laden air meets colder surfaces, leading to water droplets forming on walls, windows, and ceilings.
You may notice:
- Mould growth, particularly around windows or in corners
- Water droplets on glass or cold surfaces
- A persistent damp smell
Unlike other forms of damp, condensation is often linked to lifestyle and ventilation rather than structural defects. Introducing dehumidifiers is often a good move. However, if not addressed, it can lead to damage to paint, wallpaper and laminated finishes, and potential health concerns.
Accurate Diagnosis Matters
Many of these defects can appear similar at first glance. For example, condensation and rising damp are often confused, and timber decay can be misidentified without a detailed inspection.
A Defect Diagnosis Report provides a clear identification of the root cause along with an explanation of how the defect has developed – and crucially, practical recommendations for repair
This avoids unnecessary or ineffective treatments and ensures the issue is resolved properly.
Speak to Our Team
If you have noticed signs of damp, decay, or unusual growth in your property, early investigation is always advisable so speak to our team today.
As surveyors regulated by the Royal Institution of Chartered Surveyors, we provide clear, impartial advice to help you understand the problem and take the right next step.
