A parapet is a low wall projecting above the roof level at the edge of a flat roof, terrace, balcony, or raised walkway. It provides a degree of protection against falls at the roof edge and also conceals the flat roof membrane, insulation edge, and rainwater drainage outlets from view. Parapets are formed as an upward continuation of the external wall above roof level, typically 150-300mm above the flat roof surface, and are capped with a weatherproof coping stone (natural stone, cast stone, or concrete) or a metal coping to shed water away from the wall face.

What height must a parapet be?

Where a parapet is used as the primary means of protection against a fall at a roof edge accessible to people, it must meet the requirements of Approved Document K. The minimum height for guarding at a roof edge in a domestic building is 1100mm above the finished floor or roof surface level. Many traditional parapets are lower than this (300-600mm) and are not intended as primary fall protection - they serve to conceal the roof edge and gutter. Where maintenance access is provided to a flat roof with a parapet below 1100mm, additional temporary or permanent edge protection is required.

Why do parapets cause damp problems?

Parapets are one of the most common sources of dampness in older buildings. They project above the roof, exposing all four sides of the masonry to wind-driven rain. If the coping is cracked, if the DPC below the coping has failed, or if the flashing between the flat roof membrane and the parapet wall is damaged or missing, water penetrates the top of the wall and travels down inside it. The parapet is also susceptible to frost damage as water trapped in the masonry expands on freezing. Regular inspection and maintenance of coping joints, DPCs, and flashings is the key to keeping parapet walls dry.

What is a parapet coping?

A parapet coping is the weatherproof cap fitted to the top of a parapet wall to shed rainwater away from the wall face and prevent water entering the masonry from above. Copings are typically natural stone (sandstone, limestone, granite), cast stone, precast concrete, or aluminium/lead metal copings. A good coping should overhang the face of the wall by at least 40-50mm on each side with a throating (drip groove) on the underside to prevent water tracking back under the coping and running down the wall face. A DPC must be fitted under the coping to prevent moisture migrating down from the coping into the wall below.

Roofing noun

Parapet

/ ˈparəpɪt /

Also known as: parapet wall, roof parapet, flat roof parapet

Definition

A parapet is a low wall projecting above roof, terrace, or balcony level at the edge of a building, formed as an upward extension of the external wall. It conceals the roof edge, drainage outlets, and waterproofing membrane from view, and in some cases provides protection against falls. Parapets are capped with a weatherproof coping stone or metal coping, with a DPC below to prevent moisture descending into the wall. They are common on Georgian, Victorian, and flat-roofed modern buildings.

In practice

The parapet is one of the most maintenance-intensive parts of a building. Being exposed above the roof line on all sides, it is subjected to driving rain, frost action, and thermal cycling that the main wall below is partly sheltered from. The junction between the flat roof waterproofing and the parapet (the upstand flashing) is a critical weathering detail - lead, EPDM, or reinforced felt is dressed up the parapet face and turned over the top under the coping DPC to a minimum 150mm height above the roof surface.

Drainage of parapet-enclosed flat roofs must be carefully designed. Outlets should be positioned at the low points of the roof, with the roof falling to them at a minimum 1:80 gradient. Overflow outlets (secondary drainage) should be fitted at parapet level in case primary outlets block - these may be weep holes through the parapet or spitter outlets extending through the face of the coping. Without overflow provision, a blocked outlet on a parapet-enclosed roof will cause the roof to flood, which may lead to structural overloading and collapse.

Building Regulations

Fall protection (Part K)Guarding must be min 1100mm above roof surface if accessible

DPC under copingRequired to prevent moisture descending into wall

Upstand heightMin 150mm waterproofing upstand above finished roof level

Overflow drainageSecondary outlets required where primary outlets could block

Approved Document K requires guarding where there is a risk of falls at roof edges - parapets below 1100mm do not satisfy this requirement for accessible roofs. Approved Document H (drainage) requires overflow provision for parapet-enclosed roofs. Approved Document C requires the coping DPC and upstand flashings to prevent moisture penetration. On listed buildings and in conservation areas, replacement coping materials and profiles may be controlled by planning conditions.

Full Building Regulations guidance

Parapet

Just so you know...