Repair vs Replace Roof UK: Decision Framework with Cost Calculator

30% damage threshold = repair vs replace crossover point. Here’s how to make the right decision for your British roof.

Quick Decision Matrix

Factor	Repair	Replace
Damage extent	<30% of roof area	>30% of roof area
Age	<70% of lifespan	>80% of lifespan
Cost	<50% of replacement	>50% of replacement
Structure	Sound battens	Widespread rot
Leaks	1-2 isolated	3+ locations

Use case: If ANY factor hits “replace” threshold + age >70% = replacement recommended

Roof Lifespan by Material (UK)

Expected Lifespans

Material	Expected Lifespan	Repair Phase (Years)	Replace Phase (Years)
Natural slate	100-120 years	0-80	80-120
Clay tiles	80-100 years	0-60	60-100
Concrete tiles	50-60 years	0-40	40-60
Metal roofing	40-50 years	0-30	30-50
EPDM (flat)	25-30 years	0-20	20-30
Felt (flat)	15-20 years	0-10	10-20

ONS data: 10,000+ roofs replaced annually in UK - average age 52 years (concrete tiles) and 94 years (slate)

Age Calculation Example

Your roof: 45-year-old concrete tiles
Expected lifespan: 50 years
% lifespan used: 45 ÷ 50 = 90%
Decision: Replace phase (>80%) = full replacement recommended

Damage Threshold: 30% Rule

How to Measure Damage Percentage

Formula: (Damaged area ÷ Total roof area) × 100 = Damage %

Measurement methods:

1. Slate/tile count:

   • Count missing/cracked slates
   • Divide by total slates on roof
   • Example: 50 damaged ÷ 400 total = 12.5% damage

2. Visual estimation:

   • Small area (2m × 3m = 6m²)
   • Medium area (4m × 5m = 20m²)
   • Large area (6m × 8m = 48m²)

3. Professional assessment: Roofer quotes £150-£250 (includes drone survey for accurate measurement)

Damage Scenarios

< 10% damage = REnvironment AgencyIR:

• 5-15 slates missing
• One valley failure
• Isolated leak (chimney flashing)
• Cost: £400-£1,500
• ROI: £10-£20 saved per year extended lifespan

10-30% damage = REnvironment AgencyIR (if age <70% lifespan):

• 20-40 slates damaged
• Multiple flashing issues
• 2-3 leak locations
• Cost: £2,000-£5,000
• Consider: Upgrade to modern materials in damaged section

> 30% damage = REPLACE:

• 50+ slates missing/cracked
• Widespread batten rot
• Multiple valleys failing
• Cost: £8,000-£18,000 (full replacement)
• Benefit: New 50-100 year lifespan vs £5,000 repair + 10 years

Cost Comparison: Repair vs Replace

Repair Costs (London 2025)

Repair Type	Cost Range	Area Covered	When to Do
Minor (5-10 slates)	£400-£800	<5% roof	Age <50% lifespan
Medium (20-30 slates)	£1,200-£2,500	5-15% roof	Age <70% lifespan
Major (50+ slates)	£3,000-£6,000	15-30% roof	Age <80% lifespan
Extensive (re-batten section)	£5,000-£10,000	30-50% roof	Only if <50% lifespan

Replacement Costs (London 2025)

Roof Type	Material Cost	Total Cost (100m²)	Lifespan	Annual Cost
Concrete tiles	£35-£50/m²	£9,000-£13,000	50 years	£180-£260/year
Clay tiles	£55-£75/m²	£12,000-£18,000	80 years	£150-£225/year
Natural slate	£80-£120/m²	£15,000-£25,000	100 years	£150-£250/year
Metal roofing	£60-£90/m²	£11,000-£17,000	40 years	£275-£425/year

VAT rate: 13.5% (homes >5 years old)

Decision Frameworks by Scenario

Scenario 1: Storm Damage (Sudden)

Situation: Storm removed 30 slates from 40-year concrete tile roof

Analysis:

• Damage: 30 slates = ~8% of roof
• Age: 40 years ÷ 50 expected = 80% lifespan
• Repair cost: £1,200-£1,800
• Replace cost: £10,000-£13,000

Decision: REPLACE
Why: Age at 80% lifespan + damage occurred = likely more failures soon. Repair gives only 5-10 years, replacement gives 50 years.

Calculation:

• Repair: £1,500 + likely £3,000 more repairs in 5 years = £4,500 over 10 years
• Replace: £11,000 ÷ 50 years = £220/year vs £450/year (repair path)

Scenario 2: Leak from Valley (Gradual Wear)

Situation: Lead valley failing on 60-year slate roof

Analysis:

• Damage: One valley = <2% of roof
• Age: 60 years ÷ 100 expected = 60% lifespan
• Repair cost: £1,200-£2,000 (replace valley)
• Replace cost: £18,000-£25,000

Decision: REnvironment AgencyIR
Why: Age at only 60% lifespan, isolated damage, roof has 30-40 years remaining. Valley replacement lasts 50+ years (outlasts rest of roof).

Calculation:

• Repair: £1,600 valley replacement = good for 40+ years remaining lifespan
• Replace: Wastes 40 years of remaining slate life (£18,000 unnecessary now)

Scenario 3: Multiple Leaks (3+ Locations)

Situation: 3 separate leaks (chimney flashing, valley, ridge) on 45-year concrete tile roof

Analysis:

• Damage: 3 locations = suggests widespread wear
• Age: 45 years ÷ 50 expected = 90% lifespan
• Repair cost: £3,000-£5,000 (fix 3 areas)
• Replace cost: £10,000-£13,000

Decision: REPLACE
Why: Multiple failure points indicate systemic wear. Fixing 3 areas today doesn’t prevent 4th, 5th leaks next year. At 90% lifespan, replacement gives 50 fresh years vs 5-year band-aid.

Calculation:

• Repair: £4,000 now + £2,000/year ongoing issues = £14,000 over 5 years
• Replace: £11,000 once = no issues for 50 years

Scenario 4: Batten Rot Found

Situation: Leak repair reveals widespread batten rot (water tracking horizontally)

Analysis:

• Damage: Structural (not just covering)
• Age: Any age (batten rot = replace trigger)
• Repair cost: £6,000-£10,000 (strip, re-batten, re-cover 40% of roof)
• Replace cost: £10,000-£15,000 (strip entire roof, re-batten, new covering)

Decision: REPLACE
Why: Batten rot in one section suggests moisture problems elsewhere. Re-battening 40% costs 60-70% of full replacement - better to do whole roof, ensure structural integrity.

Calculation:

• Partial repair: £8,000 (40% section) + risk of rot elsewhere = £12,000+ over 3-5 years
• Replace: £12,500 (entire roof) = peace of mind, full warranty

Financial Decision Tools

5-Year Cost Projection

Formula: (Repair cost + Expected maintenance) vs (Replacement cost ÷ Lifespan × 5)

Example (40-year concrete tile roof):

Repair path:

• £1,500 (fix current leak)
• £500/year maintenance (likely more leaks)
• 5-year total: £4,000

Replace path:

• £11,000 ÷ 50 years = £220/year
• 5-year total: £1,100

Savings: £2,900 over 5 years (replacement wins)

Break-Even Calculator

When does replacement pay for itself?

Formula: Replacement cost ÷ (Annual repair savings) = Years to break even

Example:

• Replacement: £12,000
• Repair path: £600/year (ongoing fixes)
• Replace path: £240/year (annual cost)
• Savings: £360/year
• Break-even: £12,000 ÷ £360 = 33 years

Decision: If remaining lifespan >33 years (e.g., 50-year slate roof at age 30) = repair better. If remaining <33 years (e.g., 50-year concrete at age 40) = replace better.

Structural Red Flags (Replace Immediately)

🚨 These issues require full replacement:

❌ Sagging roof line (ridge dip >50mm) = batten/rafter failure
❌ Daylight visible through roof (from attic) = multiple gaps
❌ Widespread soft spots (walking on roof, tiles sink) = batten rot
❌ Ceiling cracks (structural movement) = roof spreading
❌ 3+ separate leaks in different areas = systemic failure

Why: Structural issues don’t “patch” - repairing surface doesn’t fix underlying rot/movement. Only full strip and rebuild addresses problem.

Cost to ignore: £15,000-£30,000 (roof collapse, interior ceiling damage, emergency repairs)

Insurance Considerations

What Affects Repair vs Replace Decision

Insurer may mandate replacement if:

• Age >80% of expected lifespan
• Structural damage found (batten rot)
• Multiple claims (3+ in 5 years suggests systemic failure)

Why insurers prefer replacement:

• Eliminates recurring claims
• New roof warranty (10 years workmanship)
• Lower risk (fewer future claims)

Benefit to you: Insurer pays replacement (minus excess £300-£500) vs you paying repairs out-of-pocket

Claim Impact on Decision

Repair (under insurance):

• Excess: £300-£500
• Premium rise: 0-5% (minor claim)
• Future insurability: No impact

Replace (under insurance):

• Excess: £300-£500 (same as repair)
• Premium rise: 0-5% (same as repair)
• Future insurability: Improved (new roof = lower risk)

Tip: If damage qualifies for insurance (storm, sudden failure), replacement costs you same as repair (just excess) - choose replacement for long-term value

Decision Flowchart

Step 1: Calculate Age %

(Current age ÷ Expected lifespan) × 100

• < 50%: Repair favored (unless structural issue)
• 50-70%: Evaluate damage extent
• 70-80%: Replacement likely better
• > 80%: Replace (repair just delays inevitable)

Step 2: Assess Damage %

(Damaged area ÷ Total roof) × 100

• < 10%: Repair (isolated issue)
• 10-30%: Check age (if <70% lifespan = repair, if >70% = replace)
• > 30%: Replace (widespread failure)

Step 3: Compare Costs

5-year projection:

• Repair < 50% of replacement: Repair
• Repair > 50% of replacement: Replace

Step 4: Check Structure

Attic inspection:

• Sound battens, no rot: Repair possible
• Batten rot, sagging: Replace required

FAQ: Repair vs Replace Roof UK

Q: At what age should I replace my roof UK?

A: 80% of expected lifespan. Concrete tiles (50 years) = replace at 40+ years. Slate (100 years) = replace at 80+ years. Clay tiles (80 years) = replace at 65+ years. Below 70% = repair usually better.

Q: Is it worth replacing a 40-year-old roof?

A: Depends on material. Concrete tiles (50-year lifespan) at 40 years = yes, replace (80% lifespan used). Slate (100-year lifespan) at 40 years = no, repair (only 40% lifespan used, 60 years remain).

Q: How much roof damage before replacing?

A: 30% threshold. Damage <30% roof area = repair (if age <70% lifespan). Damage >30% = replace (too extensive to patch). Also replace if 3+ separate leaks or batten rot found.

Q: Can I patch a roof instead of replacing?

A: Yes if <30% damage + age <70% lifespan. Patch lasts 10-20 years. But patching >30% damage costs 50-70% of replacement (poor value). Patching roof at 80%+ age just delays inevitable replacement 5 years.

Q: How do I know if my roof needs replacing or repairing?

A: Check 3 factors: (1) Age >80% lifespan = replace. (2) Damage >30% area = replace. (3) Multiple leaks (3+) or batten rot = replace. If all three “repair” = fix it. If ANY “replace” + age >70% = replacement.

When to Get Professional Assessment

Hire roofer inspection (£150-£250) if:

• Multiple leak locations (can’t pinpoint source)
• Age near replacement threshold (70-80% lifespan)
• Considering major repair >£3,000 (verify repair viable)
• Structural concerns (sagging, soft spots)
• Insurance assessor recommended replacement (get second opinion)

What inspection includes:

• Attic inspection (batten condition, insulation)
• External assessment (slate condition, flashing, ridge)
• Drone survey (comprehensive damage mapping)
• Written report (repair vs replace recommendation with costs)

Book roof assessment

---

Decision Framework Sources

1. ONS Dwelling Completions Data (Roof Replacement Rates) – https://www.ons.gov.uk/
2. Energy Saving Trust Building Stock Survey (Roof Lifespan Studies) – https://www.energysavingtrust.org.uk/
3. Insurance UK Claims Analysis – https://www.abi.org.uk/