Roof Repair or Full Replacement — How Do You Know?

The Core Question: Is the Problem Isolated or Systemic?

A single area of damage — one section of missing tiles, a failed flashing around a chimney, a section of leaking valley — is almost always worth repairing. These are isolated failures that don't indicate the rest of the roof is compromised.

The case for replacement builds when problems are recurring, widespread, or when the roof materials themselves are failing across their whole surface rather than in one spot.

Signs Your Roof Needs Repair Only

Repair makes sense when you have localised damage from a specific event like storm damage or impact. It also makes sense when flashings or valleys have failed but the main tile surface is intact, when individual tiles have slipped due to nail failure but the majority are sound, or when the roof is under 15–20 years old and has been well maintained.

Signs You May Need a Full Replacement

A full replacement is more likely the right answer when tiles are failing across the whole surface rather than in isolated areas. On Farnham's concrete tile post-war stock, this often shows up as widespread surface carbonation — the tiles become porous and start to delaminate. When this happens across the whole roof, patching individual tiles is treating symptoms rather than the cause.

Other indicators include when you've had the same section repaired two or more times in five years, when a roofing survey reveals the felt underlay has failed and is no longer providing secondary protection, when the roof is over 30–40 years old and the materials have reached the end of their design life, or when structural movement has caused widespread cracking to ridge mortar and pointing.

The Age Test

Concrete interlocking tiles have a design life of roughly 30–40 years. Clay tiles, properly maintained, can last 60–100 years. Welsh and Westmorland slate roofs on Farnham's Victorian stock can last 150 years if the slates themselves are sound — it's usually the nail fixings that fail first, not the slates.

If you don't know when your roof was last replaced, a roofer can estimate age from the tile type and fixing method during a survey. This is worth doing before committing to significant repair spend on a roof near the end of its life.

The Maths: When Does Repair Stop Making Sense?

A useful rule: if repair costs exceed 30–40% of the replacement cost, and the roof is already over halfway through its design life, replacement often makes more financial sense over a 10-year horizon. You stop spending on a failing asset and start the clock on a new one with a 10-year guarantee.

For a 3-bed semi in Farnham, full replacement typically runs £4,500–£9,000. If you're looking at £1,500–£2,000 in repairs on a 25-year-old concrete tile roof, the conversation about replacement is worth having.

Get a Survey, Not Just a Quote

The best way to make this decision is a proper roof survey rather than asking a roofer to quote for the visible problem. A survey looks at the whole roof — tiles, underlay, battens, ridge, valleys, flashings and fascias — and gives you a clear picture of overall condition. Most roofers will include a survey as part of a free quote visit.

Last reviewed: 19 July 2026