Slate Roofing Calculator
Enter slate size and head lap - the gauge and coverage are calculated automatically
Roof Slopes
75 mm for pitches = 30° - 90 mm at 25-30° - 110 mm at 20-25°
- enter slate size above
10% for straightforward roofs; 15% for complex shapes or cut slates around features
Measure the ridge and any hip lengths. Leave blank if not applicable.
Lead soakers, dry ridge units or mortar-bedded ridge tiles
Add all hip rafter lengths together
Minimum 150 mm side lap
Job Costing (optional)
UK Market Prices
Fills in the material cost fields with current UK market prices. You can review and edit each price before applying.
Results
Total Roof Area
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m²
Slates to Order
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inc. waste
Batten Gauge
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mm centres
Battens
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linear metres
Slates per m²
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coverage rate
Nails
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approx (2 per slate)
Felt Rolls
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rolls needed
Slope Breakdown
| Slope | Eaves Length | Rafter Length | Area | Slates | Battens (lm) |
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🚫 Estimate waste & skip size for this project →
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Frequently Asked Questions
How many slates do I need per square metre?
For a standard 500 x 250 mm Welsh slate with 75 mm headlap: gauge = (500 - 75) ÷ 2 = 212.5 mm. Slates per m² = 1,000,000 ÷ (212.5 x 250) = approximately 19-20 slates per m². Always add 10% for waste, cuts and breakages.
What headlap should I use for slate roofing?
At 30°+ in a sheltered location: minimum 65 mm headlap for 500 mm slates. At 20-30° or in exposed locations: 75-90 mm recommended. BS 5534 and NHBC Chapter 7.2 provide detailed minimum headlap tables based on pitch and exposure zone.
What is the difference between natural slate and fibre cement slate?
Natural slate (Welsh, Spanish, Brazilian): lifespan 60-150+ years, weight ~25-30 kg/m², premium cost, requires skilled slater. Must meet BS EN 12326. Fibre cement slate: lifespan 30-50 years, weight ~15-20 kg/m², more affordable, easier to lay. Must meet BS EN 492.
What minimum pitch is required for slate roofing?
Under BS 5534: natural slate down to 20° minimum with increased headlap in sheltered locations; 25-30° in exposed areas. Minimum pitch depends on slate size and local exposure zone per BS 8104. Most UK residential roofs use slate at 30-45°.
How many nails do I need per slate?
Each slate needs two nails, positioned ~25-35 mm from each edge at the nail hole (approximately one-third from the head). Use copper, stainless steel or silicon bronze nails - never galvanised as they corrode. Add 10% for dropped and lost nails on site.
What waste allowance should I use for slate roofing?
Simple gable roof: 10% waste. Roofs with hips, valleys, dormers or chimneys: 15%. Natural slate can break during delivery, cutting and laying - 10% is the minimum for any slate job. Order a small surplus and keep it - quarry batches vary in colour and texture, making future matching difficult.