Roof repair vs full replacement in Wales
Signs your roof needs attention
From inside the property:
- Water stains on ceilings or in the loft
- Daylight visible through the roof when in the loft in darkness
- Sagging roofline or soft spots in the loft floor
- Condensation in the loft (may indicate inadequate ventilation, not leaks)
From outside:
- Cracked, slipped, missing, or broken tiles/slates
- Damaged or missing ridge tiles
- Mortar crumbling around chimney stacks
- Sagging roof sections
- Moss and lichen buildup (accelerates tile degradation but not itself a structural problem)
- Blocked or damaged guttering causing water to overflow against the fascia
Repair vs replacement decision
Choose repair if:
- Isolated damage affecting less than 20–25% of the total area
- The underlying structure (rafters, battens) is sound
- The tiles or slates are less than 30 years old
- Flashings are intact or need only minor work
- Budget is the primary constraint
Choose full replacement if:
- More than 25–30% of tiles or slates need replacement (at this point, the cost of replacement tiles plus labour often exceeds full re-roofing)
- The roofing felt/membrane under the tiles is failing (dark staining in loft, can be felt as paper-thin when touched)
- Battens are rotten or damaged
- The roof is over 50 years old and on original materials
- Persistent leaks despite previous repairs
Welsh slate: repair or replace?
Welsh slate roofs require specific consideration:
Original Welsh slate on pre-1920 properties — Welsh slate is among the most durable roofing materials in the world; original slates from Victorian quarries routinely last 150+ years. Individual repair with quality reclaimed Welsh slate is almost always the right choice over full replacement.
Reclaimed vs new Welsh slate — quality reclaimed Welsh slate (from demolition or specialist salvage yards) is superior to both Chinese slate (shorter lifespan, more variable quality) and most "Spanish slate" (good quality but not as historically appropriate for Welsh heritage properties).
Signs original Welsh slate can be repaired: slates are sound (ring when tapped, not dull), fixings and battens are good, less than 20% of slates have failed.
Signs replacement is needed: battens have rotted (slate nails pulling through), large proportion of slates delaminating or cracked, ridge and hip work extensively failed.
Flat roof: when to replace
Flat roof replacement is one of the clearest cases where full replacement beats repair:
Felt flat roofs have a lifespan of 10–20 years. Multiple patches on a felt roof are a temporary fix — once felt is extensively cracked, blistered, or failed at seams, the right solution is full replacement.
Modern systems are significantly better than felt:
- GRP (fibreglass) — 25–30+ year lifespan, seamless, repairable, ~£70–120/m² installed
- EPDM (rubber) — 30–50+ year lifespan, highly flexible, good for complex shapes, ~£60–100/m² installed
- Both vastly outperform felt in Wales's wet climate
Never patch an old flat roof and expect it to last more than 2–3 years. A failing flat roof should be replaced entirely with a modern system.
Cost guide for Wales
| Job | Typical cost (Wales) |
|---|---|
| Repair 10 slipped/broken slates | £250–450 |
| Repoint ridge tiles | £300–600 |
| Repoint chimney stack | £400–900 |
| Replace guttering (per 5m) | £100–200 |
| Re-ridge and re-hip entire roof | £1,500–3,500 |
| Partial re-roof (25%) | £1,500–4,000 |
| Full re-roof (3-bed, Welsh slate) | £6,000–15,000+ |
| Full re-roof (3-bed, concrete tile) | £4,000–8,000 |
| Flat roof replacement (GRP, 20m²) | £1,400–2,400 |
| Flat roof replacement (EPDM, 20m²) | £1,200–2,000 |
Scaffold is required for most roof work and is typically included in quotes. If a roofer quotes without mentioning scaffold for a pitched roof job, ask explicitly whether it's included.