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Valley Design

Valley gutters must discharge into a rainwater head, sump, or an eaves gutter. The discharge point must be within 2 m of a downpipe if the catchment area exceeds 50 m².

When the roof pitch is less than 12°, the valley should be made in one piece or the joints must be sealed. To ensure snug fitting, the valley angle should be matched to the pitch of the valley support. Having the valley too open will result in a diminished capacity, and too sharp an angle will make installation difficult.

Internal Valley Angle

Roof PitchInternal Angle
176°
173°
10°166°
15°159°
20°152°
25°145°
30°139°
35°132°
40°126°
45°120°
50°114°
60°104°
(optional caption)

Maximum Valley Catchment in m² for Areas Having a 50-year Rainfall Intensity <150 mm/h

Roof Pitch10°12.5°1520°25°30°
A 3-fold  1218294170106146
B standard  2534476399140184
C Deep6086152180215251321389452
D Tile    1722334557
Free Board: 15 mm for pitches 8° and above
                      20 mm for pitches below 8°

 For other pitches, rainfall intensity, and valley shapes refer to the Capacity Calculations tool.

/cop/roof-drainage/types-gutter#valley-design
Revision Category: 
2 - Editing and rearrangement
Revision Detail: 

Removed references to "Upstand Angle B" and replaced drawing "Common Valley Shapes"