Roof Ridge & Apex Height Calculator
Vertical rise and total building apex height calculations
m
°
m
Roof Rise2.801 m
Total Apex5.201 m
Slope Factor1.2208
Direct Formula: For a symmetrical dual-pitch gable roof, vertical ridge rise from wall plate to apex is calculated as half the span multiplied by the tangent of the pitch angle: Rise = (Span ÷ 2) × tan(θ). For an 8.0m span building at 35° pitch, vertical rise = 4.0 × tan(35°) = 2.801 metres.
Ridge Height in UK Planning Permission & Permitted Development
Under UK Permitted Development Rights (Town and Country Planning Order), strict maximum ridge height limits apply to residential extensions and outbuildings:
- Single-Storey Rear Extensions: Maximum ridge height of 4.0 metres (or 3.0 metres if within 2.0 metres of a boundary).
- Outbuildings & Garages: Maximum ridge height of 4.0 metres for dual-pitch roofs, 3.0 metres for single-pitch / mono-pitch roofs, and 2.5 metres if located within 2.0 metres of a property boundary.
📚 Primary Technical Sources & British Standards
- BS 5534:2014+A2:2018: Code of practice for slating and tiling for pitched roofs and vertical cladding. British Standards Institution.
- BS 5250:2021: Management of moisture in buildings — Code of practice. British Standards Institution.
- BS 6229:2018: Flat roofs with continuously supported flexible waterproof coverings — Code of practice.
- NHBC Standards Chapter 7.2: Pitched Roofs — Minimum pitches, rafter timber sizing, batten gauges and fixing specifications.
- UK Manufacturer Technical Literature: Marley Technical Handbooks, BMI Redland Fixing Guides, CUPA Pizarras Slate Technical Manuals.
Last technical audit date: 17 August 2026.