A shadow gap is a deliberate recess where two surfaces meet — most often where a ceiling meets a wall, or where one ceiling material meets another. Done well, it reads as a crisp dark line that makes the ceiling appear to float. Done badly, it reads as a mistake.
This guide covers how shadow gaps are formed in commercial ceilings, what dimensions work, and when an extruded channel is the right route.
Three ways to form a shadow gap
Site-formed plasterboard detail. Battens, boards and stop beads, cut and skimmed by hand. Cheap in materials, expensive in labour, and the line is only as straight as the operative's eye. Fine for a single domestic room. Risky over a 30-metre run in a Cat A office.
Plaster-in trims. Light-gauge folded or roll-formed sections skimmed into the board. Faster than site-forming, but folded sheet holds a soft arris — the shadow edge rounds off — and thin sections deform in transit and handling.
Extruded recessed channels. A precision-extruded aluminium C channel fixed into the ceiling build-up. The geometry is held by the die, not the installer, so the gap width and reveal depth are identical at metre 1 and metre 40. This is the REVEAL system's route.
Dimensions that work
Perimeter shadow gaps typically run 10–20mm; feature gaps between materials run wider. REVEAL channels are stocked in 100, 125, 150, 200 and 300mm face widths for details that also carry services — lighting, sprinklers, detection — inside the gap rather than beside it.
Junction details
Detail drawings coming shortly: REVEAL at plasterboard ceiling, REVEAL between plasterboard and acoustic raft, REVEAL perimeter to wall. Each will be available as a DWG on the downloads page.
Extruded vs folded — why it matters at the shadow line
A shadow gap is pure geometry. Any waviness, rounded edge or dent is immediately visible because the detail is nothing but line and shadow. Extrusion holds a sharp arris and resists site deformation; folded sheet does neither.
Specifying REVEAL
UK-extruded, UK-stocked, 100% recycled aluminium, despatched in 5 working days. Data sheets and CAD on the downloads page. Send your detail and we'll return coordination notes.