A gutter (or rainwater gutter) is a channel fixed along the eaves of a roof that collects rainwater running off the roof tiles or slates and directs it via downpipes to a drain, soakaway, or water butt. Without gutters, roof runoff falls to the ground directly against the walls, causing water penetration, damp, erosion of pointing, and foundation saturation. Gutters are fixed to the fascia board at the eaves, set at a slight fall (typically 1:600) towards the downpipe outlet.

What are the different types of gutter?

Half-round gutters are the most common domestic profile - a simple semicircular channel, typically 112mm wide for standard houses. Ogee gutters have an S-shaped decorative profile and are common on Victorian and Edwardian properties. Square (box) gutters have a rectangular section and are used on larger commercial properties or behind parapet walls. Cast-iron gutters were standard until the mid-20th century and are still required on listed buildings and in many conservation areas for repair/replacement. Modern gutters are typically uPVC (cheap, lightweight, low maintenance) or aluminium (longer-lasting, can be colour-coated).

How should gutters be sized?

Gutter capacity must be sufficient to handle the peak rainfall from the roof area it serves, using the design rainfall intensity for the location. BS EN 12056-3 (Roof drainage) provides the calculation method. For most standard UK houses, 112mm half-round gutters with 68mm round downpipes are adequate. Larger roofs (L-shapes, wide frontages) or high-rainfall locations (Wales, Scotland, upland areas) may need 125mm or 150mm gutters. Undersized gutters overflow in heavy rain - typically seen as water pouring over the gutter front between downpipes. Adding more downpipes is often more effective than upsizing the gutter profile.

Where should gutter water discharge to?

In England and Wales, surface water (including roof rainwater) must not be discharged to a foul (sewage) drain without approval from the water authority - the two systems are kept separate to prevent overloading sewage treatment works in heavy rain. Roof water should discharge to: a dedicated surface water sewer; a soakaway (if ground conditions allow); a watercourse (with riparian rights and possibly consent); or a sustainable drainage system (SuDS) such as a permeable surface, rain garden, or rain harvesting tank. Where no existing surface water drain exists, a soakaway is the most common domestic solution.

Roofing noun

Gutter

/ ˈɡʌtə /

Also known as: rainwater gutter, eaves gutter, half-round gutter, ogee gutter, box gutter

Definition

A gutter is a channel fixed along the eaves of a roof to collect rainwater running off the roof slope and direct it via downpipes to a drain, soakaway, or water butt. Gutters are fixed to the fascia board with a slight fall (1:600 typically) towards the downpipe outlet. Common profiles are half-round (most domestic), ogee (Victorian/Edwardian), and box/square (commercial). Materials include uPVC, aluminium, cast iron, and steel.

In practice

Blocked or overflowing gutters are one of the most common causes of damp problems in older properties - water running down the wall face instead of into the drain saturates the masonry, causes efflorescence, penetrates mortar joints, and can lead to rising damp and internal water damage. Gutters should be cleared of leaves and debris at least annually (more often for properties with overhanging trees). Valley gutters and secret gutters (concealed within the roof slope) require particular attention as blockages are not immediately visible but cause significant damage when they occur.

For new extensions, gutter and downpipe sizing should be calculated to BS EN 12056-3, using the effective roof area and local design rainfall intensity. Standard 112mm half-round gutters with 68mm round downpipes serve most domestic applications. Downpipes should connect to a trapped gully before the underground drain to prevent foul gases entering the rainwater system. Where surface water sewers are not available, a soakaway must be designed to BS EN 752 and positioned at least 5m from any building.

Building Regulations

StandardBS EN 12056-3 - Roof drainage layout and calculation

DischargePart H - surface water must not go to foul drain

Soakaway setbackMinimum 5m from any building foundation

Conservation areasCast-iron replacement required on historic buildings

Approved Document H (Drainage and waste disposal) requires surface water from new buildings and extensions to be discharged in a sustainable manner - to surface water sewers, soakaways, or watercourses. Connection to foul drains is not permitted for roof water without specific approval. New development in flood risk zones may be required by the LPA to incorporate SuDS (sustainable urban drainage systems) to reduce peak surface water runoff rates. BS EN 12056-3 provides the hydraulic design method for sizing gutters and downpipes.

Full Building Regulations guidance

Gutter

Just so you know...