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Flat Roof Fall Calculator
Calculate the required height difference, fall ratio, and drainage gradient for flat roofs. Compliant with BS 6229 and BS 8217 minimum 1:80 fall recommendations.
📐 BS 6229 compliant
💧 Drainage gradient
⚡ Instant results
Roof Fall Calculator
Enter your roof dimensions to calculate required fall
Calculation Mode
Choose which measurement to work out
Roof Dimensions
m
Horizontal distance from highest to drainage point
1 : X
e.g. 80 = 1:80 · minimum recommended is 1:80 (BS 6229)
Roof Details
Material affects recommended minimum fall
m
Used to calculate total roof area
Fall Summary
Your flat roof drainage calculations
Enter your roof dimensions and fall ratio, then click Calculate fall to see your drainage requirements.