Part H · England · Free to use
Gutter and outlet size calculator
Effective roof area from pitch, then the half-round gutter and outlet size it needs.
Approved Document H (2015)
Your inputs
Results update as you type.
m²
°
Part H · Result
125 mm gutter, 75 mm outlet
Effective roof area 57.1 m².
Checks passed- Pitch factor: Calculated resultTable 1, interpolated1.36
- Effective roof area: Calculated resultplan area × factor57.1 m²
- Area per outlet: Calculated result57.1 m²
- Flow capacity: Calculated result1.37 l/s
- Table 2 assumes a half-round gutter laid level with a sharp-edged outlet; rounded outlets and falls increase capacity.
Clauses this relies on
Source edition and scope
Approved Document H (2015).
This is a preliminary check of the conditions shown. Confirm the edition, project circumstances and any additional requirements with your architect or building control.
A design aid, not legal advice. Checked against the Building Regulations 2010 for England; confirm with building control.