Roof pitch UK: minimum and maximum angles by material
Roof pitch is the angle of the slope, measured in degrees. UK roofs range from 1° (flat) to 70°+ (mansard lower section). Each covering material has a minimum pitch below which it will leak.
Minimum pitch by material (BS 5534)
| Material | Minimum pitch | Why |
|---|---|---|
| EPDM / GRP / felt (flat membrane) | 1-5° | Continuous waterproof layer, no joints to leak |
| Profiled metal sheeting | 5-10° | Long sheets, end laps need fall to shed water |
| Standing seam metal (zinc, copper) | 3° | Welded joints, near-flat capable |
| Concrete interlocking tile | 17.5° | Interlocks shed water at low pitch |
| Slate (large, 600×300mm) | 20° | Overlap shed water |
| Slate (small, 400×200mm) | 25° | Smaller laps need steeper angle |
| Plain clay tile (single lap) | 30° | No interlock, water relies on gravity |
| Pantile (clay) | 30° | Single lap with profile drainage |
| Thatch | 45° | Bundles shed water by steep run-off |
Source: BS 5534:2014+A2:2018 (Code of practice for slating and tiling for pitched roofs and vertical cladding).
How to measure roof pitch
Method 1: Inside the loft. Hold a spirit level horizontally against a rafter. Measure the vertical drop over 12 inches (300mm). Use the table:
- 3" drop / 300mm run = 14° (1-in-4 pitch)
- 4" drop / 300mm run = 18° (1-in-3 pitch)
- 5" drop / 300mm run = 22.5°
- 6" drop / 300mm run = 26.5°
- 7" drop / 300mm run = 30°
- 9" drop / 300mm run = 36°
- 12" drop / 300mm run = 45°
Method 2: Outside, using a smartphone level app held against a rafter or roof edge. Less accurate but easier.
Method 3: From the ground, measure the span (eaves to eaves) and the rise (eaves to ridge). Pitch = arctan(rise ÷ half-span).
- Cheapest UK pitch
- 30-35° (standard rafter lengths, common tile sizes)
- UK British Standard
- BS 5534:2014+A2:2018
- Flat / pitched boundary
- 10° (Building Regulations)
- Steepest UK roof type
- Mansard lower section (70-80°)
What happens below minimum pitch?
Water gets driven sideways by wind, capillary action pulls it back under the lap, and eventually it tracks down inside the covering. You get damp patches on bedroom ceilings, rot in rafters, and stained insulation. The fix is either a sub-roof membrane (works for shallow under-pitch shortfalls) or re-pitching the roof (major structural work, often cheaper to demolish and rebuild).
Many late-1970s concrete-tile estate homes were built at 22-25° which was the minimum at the time. Tightening of BS 5534 in 2014 means some of those would now fail. If you re-cover, your installer may need to add an underlay upgrade (£200-£500).
Maximum pitch
There's no hard maximum, but practical issues: above 60° tiles and slates need extra clips to stop them slipping under their own weight (£3-5/m² extra material). Above 70°, you're functionally on a wall, not a roof.
Sources
- British Standards Institution, BS 5534:2014+A2:2018 Code of practice for slating and tiling
- National Federation of Roofing Contractors, Pitched roof minimum slope guidance, 2024
- NHBC Standards 2025, Chapter 7.2 Pitched roofs
Last reviewed: 2026-05-18