In our 20+ years surveying properties across Acton, Ealing, and West London, roof and drainage defects consistently rank in the top three most expensive and most commonly found issues. A failing roof on a three-bedroom Victorian terrace can cost £20,000–£35,000 to replace. A failed drain can undermine foundations, cause subsidence, and introduce damp — the total remediation cost running to tens of thousands of pounds. This is why a thorough survey is essential before you buy.
External drainage and guttering inspection is a key part of every Acton Surveyors building survey.
Part 1: Roof Defects in London Properties
The Anatomy of a Victorian Roof
Most Victorian and Edwardian houses in West London have a pitched roof covered in Welsh slate, with clay ridge and hip tiles. The roof frame is typically a cut-rafter construction with timber rafters, purlins, and ceiling joists. The underside is lined with bitumen-impregnated roofing felt (or in older properties, no felt at all — just bare tiles).
These roofs are now 100–130 years old. Original Welsh slate can last 150+ years if undisturbed — but decades of patching, re-nailing, and inappropriate cement repairs have often compromised their integrity.
What Our Surveyors Look for on Roofs
Roof inspections at both Level 2 and Level 3 are conducted from ground level using binoculars, and internally from the loft hatch. A drone inspection can provide additional coverage where requested. We look for:
- Slipped or missing slates/tiles: Each missing slate allows water to penetrate immediately. Multiple slipped slates indicate nail sickness — the iron nails holding the slates are corroding and failing throughout the roof, typically requiring a full re-cover.
- Ridge and hip tiles: Mortar-bedded ridge tiles dry out, crack, and dislodge over decades. Loose ridge tiles are a safety hazard and allow water ingress at the apex of the roof.
- Flashings: Lead, zinc, or felt flashings seal the junction between the roof and chimney stacks, dormer cheeks, and parapet walls. Failed flashings are one of the most common routes for water into Victorian properties.
- Flat roofs: Bay window, kitchen extension, and garage flat roofs are common in West London properties and have a much shorter life than pitched roofs — typically 15–25 years. Blistering, pooling water, and splits in the felt are common findings.
- Guttering and rainwater goods: Cast iron gutters were standard until the 1970s — they are prone to cracking and overflow when blocked. Overflowing gutters directly cause penetrating damp in solid-walled Victorian properties.
Typical Roof Repair Costs in London (2025)
| Work Required | Approximate Cost |
|---|---|
| Partial re-tile/re-slate (up to 25%) | £3,000 – £8,000 |
| Full re-cover (Welsh slate, 3-bed terrace) | £18,000 – £35,000 |
| Ridge tile re-bed and repoint | £800 – £2,500 |
| New lead flashings (chimney stack) | £600 – £1,800 |
| Flat roof replacement (GRP/single ply) | £1,500 – £5,000 |
| Cast iron guttering replacement (run) | £400 – £1,200 |
Part 2: Drainage Defects in London Properties
Why Drainage Matters More Than You Think
The drainage system of a London Victorian property is typically 100+ years old. Clay pipes laid in Victorian times were jointed using putty or mortar, both of which deteriorate over time. Root ingress from garden trees and shrubs is extremely common — particularly in Ealing, Acton, and Chiswick's leafy streets.
A failed drain is not just a plumbing inconvenience. Leaking drains can:
- Saturate and soften the ground beneath foundations — contributing to subsidence
- Introduce ground moisture that migrates into the property as rising damp
- Cause sinkholes or voids in garden paths and driveways
- Create health hazards from sewage contamination
What Our Surveyors Check
During our building surveys, we carry out a visual inspection of:
- Accessible manholes — flow, condition, and any evidence of root ingress or blockage
- External drainage — rainwater downpipes, connection to drains or soakaways
- Any visible signs of drain failure — sunken paths, wet patches, persistent damp adjacent to drains
Where concerns are identified, we recommend a CCTV drainage survey. This involves a specialist contractor threading a camera through the drainage system to identify cracks, disjointed pipes, root ingress, and collapses. Cost: typically £150–£350 for a residential property.
Common Drainage Defects We Find
- Root ingress: Tree roots, particularly from common oak, plane, and willow trees, find their way into jointed clay drainage pipes and grow to block or break them
- Pipe displacement: Settlement, tree roots, or poor workmanship causes pipes to separate at joints, allowing leakage into the surrounding ground
- Collapsed sections: Old or overloaded pipes can collapse entirely, requiring excavation and replacement
- Shared drains: Many Victorian terrace properties share drainage with neighbours — a "Section 24 agreement" may be required when carrying out repairs
- Blocked soakaways: Properties that use soakaways for surface water drainage can experience garden flooding when soakaways become silted up
Red Flags to Watch For Before You Even Get a Survey
When viewing a property, look out for these warning signs of potential roof and drainage problems:
- Damp staining on ceilings (especially upper floor) — suggests roof leak
- Moss or vegetation on the roof — indicates failing tiles/slates and poor drainage
- Sagging gutters or rust stains on external walls — blocked or failed guttering
- Sunken or uneven paths near drain runs — possible drain failure below
- Persistent damp at ground floor level — possibly related to drainage issues
- An unusually lush or green strip of garden — could indicate an underground drain leak
Frequently Asked Questions — Roof and Drainage
Should I get a CCTV drain survey for every property purchase?
Not necessarily, but we strongly recommend it for any Victorian or Edwardian property, any property with large trees in the garden, or where a drain runs under a structure. The cost (£150–£350) is trivial compared to the cost of discovering a major drainage failure after purchase.
What is nail sickness and how serious is it?
Nail sickness describes the widespread corrosion of iron nails used to fix slates to roof battens — a common condition in Victorian and Edwardian roofs. As the nails corrode, slates begin to slide and fall. A roof with nail sickness typically cannot be repaired slate-by-slate — a full re-cover is required. This is one of the most significant and costly roof defects.
Can I use the roof condition to negotiate the purchase price?
Yes. A failing roof is one of the most commonly used and most successful grounds for renegotiation. Obtain contractor quotes for the full re-cover and use these to support a price reduction request. See our guide: How to Renegotiate After a Survey.
Does buildings insurance cover drainage defects?
Most standard buildings insurance policies do not cover gradual deterioration of drainage. They may cover sudden and unforeseen events (e.g., a pipe collapsing due to a one-off event). Gradual root ingress or pipe degradation is typically not covered and is a maintenance liability.
To discuss any concerns about a property's roof or drainage before you buy, contact Acton Surveyors. Our Level 3 Building Survey provides the most detailed assessment of both roof and drainage systems available.