upstand

An upstand is the vertical portion of roof flashing or membrane that rises up against a wall, chimney, parapet, or other vertical surface. It bridges the gap between the sloping or flat roof plane and the vertical obstruction, preventing water from running down the wall behind the roofing material. The upstand is typically formed from the same material as the main roof covering, whether that is lead, zinc, asphalt, felt, or modern membrane systems.

The height of an upstand varies by code and application. Building regulations generally require a minimum of 150 mm above the finished roof surface where it meets a vertical wall, though this can increase to 225 mm or more in exposed locations or where snow load is a concern. The upstand extends typically 100 to 150 mm horizontally across the roof plane before the slope begins, creating a solid bond line. On pitched roofs, the upstand sits above the roof covering; on flat roofs, it may be fully integrated into the membrane system.

Common failure points occur where the upstand meets both the roof plane and the vertical surface. If the upstand is too low, wind-driven rain can bypass it and penetrate behind the flashing. Poor adhesion between the upstand and the wall, usually caused by dirt, loose mortar, or inadequate priming, leads to water ingress along the joint. Upstands on parapets must withstand thermal movement without cracking or tearing; metal upstands rely on proper expansion joints to accommodate building movement, while polymeric membranes must have sufficient elasticity.

Installation and Materials

In traditional lead or zinc work, the upstand is dressed up the wall face and tucked into a horizontal chase cut into the masonry, then sealed with mortar or sealant. The top edge is either tucked into a raglet (a prepared groove) or finished with a cover flashing. Modern membrane systems often fuse the upstand as a continuous extension of the base membrane, with additional layers or reinforcement strips applied at the critical junction. The material choice affects durability: lead has excellent longevity but high cost and handling constraints; polymeric membranes are lighter and faster to install but require compatible adhesives and careful sealing of overlaps.

The term 'upstand' reflects its simple function: it stands up where the roof ends. In practice, the upstand performs much of the work that simpler flashings cannot, because it provides height, surface area for secure bonding, and a physical barrier to capillary action and wind pressure. On high-rise buildings, parapets, and mechanically complex roofs, the integrity of the upstand often determines whether a roof system lasts its intended service life or fails prematurely in the first significant weather event after installation.