London’s housing stock is some of the oldest and most varied in the UK — Victorian terraces, converted mansion blocks, post-war estates, and new-build flats all sitting side by side. That variety is part of the city’s charm, but it also means certain building defects turn up again and again, regardless of how well a property has been maintained on the surface. Knowing what to look for — and what it means when you spot it — can save you from a nasty, expensive surprise down the line.

Here are 7 of the most common building defects we come across during surveys across London.

1. Subsidence and Structural Movement

Large parts of London sit on clay soil, which expands and contracts with moisture levels — a major cause of subsidence, especially during long dry spells. Warning signs include diagonal cracks wider than a 10p coin (particularly around windows and doors), doors and windows that stick without an obvious reason, and cracks that appear to be getting wider over time rather than staying the same.

Not every crack means subsidence — most are simple cosmetic settlement — but it’s exactly the kind of thing a Level 3 Structural Survey is designed to properly investigate and diagnose.

2. Damp and Condensation

Damp is one of the most frequently flagged issues in London properties, particularly in older buildings and converted flats. It generally falls into three categories: rising damp (moisture travelling up through walls from the ground), penetrating damp (water getting in through the external fabric of the building), and condensation (caused by poor ventilation, common in converted flats without adequate airflow).

Left untreated, damp damages plaster, timber, and decoration, and can eventually lead to more serious issues like timber decay.

3. Roof Defects

Roofs take the most weather punishment of any part of a building, and problems are often invisible from the ground. Slipped, cracked, or missing tiles, deteriorating flashing around chimneys, and worn flat roof coverings (common on Victorian rear extensions and conversions) are among the most common issues we find.

Because roofs are difficult and risky to inspect properly from a ladder, we include a free drone survey with every structural inspection, so nothing gets missed simply because it was hard to reach.

4. Timber Decay and Woodworm

Wet rot, dry rot, and woodworm are all common in London’s older timber-framed structures — particularly in roof spaces, floor joists, and window frames. Dry rot is the most serious of the three, as it can spread through masonry and cause widespread structural damage if it isn’t caught early.

These issues are often hidden behind floorboards or within roof voids, which is exactly why a proper internal inspection matters far more than a quick visual walkaround.

5. Poor or Outdated Electrics

Many London properties still have electrical installations that are decades old, especially in homes that haven’t been rewired since conversion. Common red flags include old fuse boxes instead of modern consumer units, exposed or frayed wiring, and a lack of residual current device (RCD) protection — a modern safety standard.

A full survey only covers a visual assessment of electrics, so if anything looks dated, it’s always worth commissioning a dedicated electrical inspection condition report (EICR) before or shortly after purchase.

6. Defective Guttering and Drainage

Blocked, cracked, or poorly fitted guttering is a small problem that causes big damage over time — water that should be carried away instead runs down walls, seeps into foundations, or pools around the base of the building, contributing to damp and even subsidence. It’s one of the most overlooked defects simply because it’s rarely checked until there’s already visible damage elsewhere.

7. Unauthorised or Substandard Alterations

London has a high number of loft conversions, basement extensions, and knocked-through walls — and not all of them were carried out to building regulation standards or with the correct approvals. Removed load-bearing walls without proper support, loft conversions without adequate fire safety measures, and extensions built without building control sign-off can all create serious structural and legal headaches for a new owner.

This is one of the most important reasons to have a professional survey carried out before buying — it’s far easier to negotiate on price or ask questions before you own the problem.

Don’t Buy Blind — Get a Proper Survey First

Most of these defects aren’t obvious during a casual viewing, and some aren’t visible at all without a trained eye and the right inspection. A Level 2 HomeBuyer Report covers the basics for standard properties, while a Level 3 Structural Survey is the right choice for older, altered, or more complex properties — both backed by a free drone roof survey as standard.

See all our survey services or contact us for a free, no-obligation quote.