Degrees and percentages are different
Pitch in degrees is the angle between the roof and a horizontal line. Percentage slope is rise divided by horizontal run, multiplied by 100. A rise of 1 metre over 2 horizontal metres is a 50% slope, approximately 26.6°. A 45° roof has a 100% slope. Do not use a percentage value as if it were a degree value.
Obtain a usable measurement
Use drawings or a measurement made during a safely arranged roof inspection. A photograph can help describe the roof but perspective makes it unreliable as the sole pitch measurement. Record the pitch of each distinct slope, especially around dormers, extensions or changes in roof angle. Do not climb onto the roof merely to measure it.
Read the conditions beside the minimum
A published minimum pitch may require a particular underlay, sealed joints or additional measures. Exposure, slope length and roof geometry can also affect the specification. For example, the Tuile du Nord 993 sheet gives 25° and refers lower pitches for additional advice. This is a model-specific instruction, not a rule for all clay tiles.
Ask the roofer to record the chosen tile, batten gauge, headlap, underlay and fastening plan together. If the existing pitch is outside the normal application range, obtain the manufacturer’s project-specific confirmation before ordering. A solar mounting system’s pitch range does not establish that the roof tiles are suitable at that angle.
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Technical sources
Checked on 23 September 2026.
Apply this to your roof
Record your preferences in the roof plan. Final dimensions, product suitability and the complete build-up are assessed for the actual roof; keep the agreed details and manufacturer instructions with your project documents.