Parapet (Roof)

A parapet is a barrier that continues a wall upward at the edge of a roof, terrace or balcony. The word comes from the Italian parapetto, meaning "chest guard". Parapets originated as defensive walls but are now standard on many low-slope roofs.

Functions

• Fall protection: acts as a guard at the roof edge.
• Fire: fire walls often extend above the roof as parapets of equal fire resistance to limit fire spread, as required by building codes.
• Wind: parapets modify wind flow over the roof, influencing uplift at corners and edges.
• Concealment: hides rooftop equipment.
• Drainage: contains water on the roof, which is why roofs with parapets need drains or scuppers and overflow drainage.

Roofing at parapets

The membrane turns up the inside face of the parapet as a base flashing. UK guidance generally calls for waterproofing to extend at least 150 mm (6 in) above the finished roof surface. Above that, a counterflashing, reglet or termination bar protects the top edge, or the membrane continues up and over the parapet under the coping. Cants or angle fillets are sometimes used at the junction with bituminous membranes.

Problems

Parapets are frequent sources of leaks: water can enter through cracked masonry, mortar joints, failed copings or unsealed laps and run down inside the wall to appear far from its entry point. Parapet walls are exposed on both faces and suffer freeze-thaw damage, so many designs include through-wall flashings, cavity trays and robust copings.

Related elements

The top of a parapet is protected by a coping. Overflow scuppers are often set through parapets.