Roof Drainage Calculator
Roof & Rainfall
Total effective drainage area
Tashkent: 80–100 | Istanbul: 100–120 | London: 75 | Dubai: 25
Flat roof: 1.0 | Gravel: 0.9 | Green roof: 0.5–0.7
Drain Points
EN 12056-3: minimum 2 per drainage area
Vertical Pipe (Downpipe / Stack)
EN 12056-3 Table 4 — vertical stacks typically 1/3
Horizontal Pipe (Collector)
EN 12056-3 Table 5 — horizontal collectors
Min 0.5% recommended | Typical: 1–2%
Roof Drainage Calculator
EN 12056-3 gravity roof drainage design. Q = C × r × A / 3600. Sizes vertical stacks and horizontal collectors with configurable fill ratios.
Key Points:
- EN 12056-3 gravity roof drainage standard
- Q = C × r × A / 3600 design flow formula
- Separate sizing for vertical and horizontal pipes
- Configurable fill ratios per EN 12056-3 Tables 4 & 5
- Minimum drain point recommendation
- Manning's equation with exact partial-flow bisection
- Standard pipe sizes: DN50 to DN315
Calculation Steps:
- Enter all required parameters
- Click "Update Calculation"
- Review results and analysis
Formula Variables:
Q
Total Design Flow
(L/s)
C
Runoff Coefficient
(–)
r
Rainfall Intensity
(mm/h)
A
Roof Area
(m²)
n
Manning's n
(–)
D
Pipe Diameter
(mm)
S
Pipe Slope
(%)
φ
Fill Ratio
(–)