Custom exterior window sills — folded coated steel

Water running down the glass and window frame should leave the building beyond the façade surface. An external sheet metal sill provides that route, protecting the bottom of the opening and the wall finish. Low weight, formability and a factory coating make metal well suited to this role. It is a practical detail for new windows and insulation upgrades, when the insulation thickness and required coverage change.

The sill’s function depends on its cross-section. A sloping surface directs water outwards, and a suitably formed front edge helps droplets detach from the underside. This prevents water from simply tracking back beneath the sill directly onto the render. Side terminations complete the protection at the reveals. The folded sheet therefore forms a cover whose effect comes from its shape. Its projecting edge separates the path of falling droplets from the render surface. For the owner, this improves protection in an area that receives runoff from the whole window during rain. It is particularly useful on a newly finished façade, where a correct detail helps limit water stains and local dampness.

Sheet metal can be formed to the required width and length, making the sill easier to fit to an existing window. When a building is insulated, the new cover can span the thicker wall while maintaining the right projection. Compared with a heavy stone sill, a metal component is lighter and easier to use where low loading or straightforward replacement matters. Its slim cross-section also keeps the lower window detail visually light. Custom folds provide flexibility around older frames and unusual reveals. Where the building requires a different geometry, the solution need not depend on one standard size. For openings of varying widths, a common profile and colour can be retained while adjusting the length of each sill.

The factory-coated surface protects the metal substrate and allows the sill to match the windows, roof or other flashings. It can create a quiet, uniform finish or a more distinct accent below the opening. The ready-applied coating helps keep the colour consistent across all sills, without separate on-site painting. Its smooth surface makes ordinary dirt easier to remove, and the simple profile is easy to inspect during a façade check. Repeated across many windows, the sill brings visual order to the wall. Its value therefore lies in drainage, low weight and architectural fit working together. A well-chosen detail completes the window area in a way that supports both building protection and appearance.

SteelProfil helps select sheet metal sills for the wall depth and planned finish. We offer frequent promotions and very competitive prices. Our broader range includes first- and second-grade materials available from stock, making it convenient to assemble the remaining flashings as well.