raggle

A raggle is a horizontal or vertical groove cut into a masonry wall, typically 25 to 50 mm deep, designed to receive and lock in place a metal flashing component. The flashing itself, called a reglet, slides into this slot and is then pointed (sealed) with mortar or sealant to create a weathertight joint. This mechanical keying prevents water from running behind the flashing and migrating into the wall cavity or structure beneath.

Raggles are most commonly found where a roof meets a vertical masonry wall, at parapets, at the junction between brick and a window or door frame, and at other locations where flashing must create a reliable water barrier. The groove must be cut during construction or retrofitted with care; it runs perpendicular to the flashing direction and is often positioned in the mortar joint between bricks or stones, though it can also be cut directly into the masonry unit itself. Depth and width are critical: if the raggle is too shallow, the flashing will not be fully captured; if cut too wide or deep, structural integrity may be compromised.

The reglet inserted into the raggle is usually aluminum, zinc alloy, or stainless steel, with a back leg that extends into the wall cavity and an outer leg that angles to shed water. Some reglets have a splay or foot that helps distribute load across the base of the groove. After insertion, the outer edge of the reggle is mortar-pointed flush with the surrounding masonry, and the underside of the flashing is often bedded in mortar or mastic to seal the base.

Poor raggle work is a common source of building failure. Raggles cut too wide can weaken the wall; those cut at the wrong angle will trap water instead of shedding it. If the reglet is not fully seated or if the pointing fails, capillary action will draw moisture into the wall structure, leading to spalling, efflorescence, and internal corrosion. In older buildings, raggles may have been sealed only with lime mortar, which eventually erodes and fails.

The term raggle likely derives from an Old English root meaning to scratch or scrape, reflecting the cutting process itself. It is primarily British and Commonwealth terminology; North American practice often uses the word reglet alone to refer to both the groove and the component, though the distinction is useful for clarity on site.