combing ridge

A combing ridge is the uppermost course of roofing slates installed along the peak of a pitched roof, positioned so that its slates project above the main ridge line. These slates overlap and interlock at the apex where two roof slopes meet, forming a weathertight seal at the highest and most exposed point of the roof. The slates are laid with their tails (lower edges) visible and their heads (upper edges) concealed beneath the next course, following the same principle as all slate coursing, but with the additional requirement that they must manage water that flows down both slopes toward the ridge itself.

The combing ridge performs a critical function: it prevents wind-driven rain and snow melt from penetrating the roof at the peak, where water naturally congregates. Because the ridge is a convergence point of two slopes meeting at an acute angle, the combing slates must be positioned and secured to resist both vertical water penetration and horizontal wind pressure that can force water under the tail edges. Traditionally, the topmost slates are either bedded in mortar or secured with copper or slate pegs driven through pre-drilled holes, depending on the roof's age and the builder's practice.

Material and dimension

Combing ridge slates are typically thicker and more robust than the general field slates below them, often 10 to 13 mm in thickness rather than the 6 to 8 mm common in the main roof. They are usually cut to lengths between 400 and 600 mm and widths around 250 to 300 mm. The slate must be of sound quality without active lamination or splitting tendencies, since the ridge course endures concentrated thermal cycling and wind stress. Regional stone determines appearance; Cornish, Welsh, and French slates each produce different colors and texture at the combing ridge.

The combing ridge is distinct from a ridge capping or ridge tile used in clay or concrete tile roofing. In slate work, there is no separate ridge tile; instead, the slates themselves form the ridge detail, which demands precise laying and alignment. Poor combing ridge work, such as slates that are too shallow, incorrectly pitched, or bedded in defective mortar, is a common source of water ingress and subsequent rot in roof timbers, particularly in older properties where repointing has failed.