Roof Pitch / Tilt Angle explained
Roof pitch (also called tilt angle when referring to solar panels) is the angle of your roof surface relative to horizontal. A flat roof has 0° pitch; a typical UK semi-detached has around 35–40°; a steep Victorian terrace might be 45–50°.
For solar panels in the UK, the optimal tilt angle is approximately 30–35°, which maximises annual energy capture by aligning panels most closely with the average angle of the sun above the horizon throughout the year.
How different pitches compare (for a south-facing roof in the UK):
- 0° (flat): ~87% of optimal annual output
- 15°: ~96% of optimal
- 30–35°: ~100% (optimal)
- 45°: ~98% of optimal
- 60°: ~88% of optimal
The good news: the output difference between a 25° and a 45° pitch is relatively small. Most standard UK roofs fall within the acceptable range. Flat roofs are worth noting: panels are often mounted on angled frames at 10–15° to aid self-cleaning and generate reasonable output, though this adds cost.
Steep roofs (above 50°) can also cause reflective losses in summer when the sun is high. Your installer's PVGIS or similar software will calculate accurate output predictions for your specific pitch.