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Engineering ToolBox > Gutter Slopes and Roof Drainage
Recommended size of gutter slopes draining roofs can be found in the table below.
| Roof area | |||||||
| Guttering diameter | Slope of | ||||||
| mm | inches | 0.5% | 1% | 2% | |||
| m2 | ft2 | m2 | ft2 | m2 | ft2 | ||
| 80 | 3 | 16 | 170 | 22 | 240 | 32 | 350 |
| 100 | 4 | 33 | 360 | 47 | 510 | 67 | 720 |
| 125 | 5 | 58 | 625 | 82 | 880 | 116 | 1250 |
| 150 | 6 | 89 | 960 | 126 | 1360 | 178 | 1920 |
The table is based on a rainfall intensity of 100 mm per hour (4 inches per hour). The anticipated rainfall intensity should always be checked with the local authorities.