A bead is a rounded, convex edge along the side of a building element. You find it on a flat roof edge, on a zinc or timber gutter, under a window board and in plasterwork. In Dutch it is called a kraal, a word related to curl.
Where beads appear
- Roof edge — in sheet metal work the edge of the strip is turned over into a bead. That stiffens the edge, removes a sharp cut edge, and makes rainwater break away cleanly.
- Gutter — the front edge of a zinc gutter is finished with a bead, often formed around a wire. That keeps the gutter edge straight and stops it deforming when someone leans a ladder on it.
- Under a window board — a beaded board with a half-round nose, so water drips off the underside instead of running back to the wall.
- In plasterwork — a bead as a rounded transition at a reveal or a ceiling junction.
- In joinery — a half-round moulding along a matchboard, a door panel or a moulding.
Why the rounded shape
A bead is not only decoration. The shape does three things at once:
- Stiffness. A turned edge is far stiffer in bending than a flat strip of sheet. That is why every piece of sheet metal work has its edge turned over.
- Shedding water. A convex bottom edge acts as a drip: water releases at the lowest point instead of tracking along the surface underneath.
- Resistance to damage. A curve absorbs a knock; a sharp arris in paint or plaster chips off.
In practice
With sheet metal, allow for movement: zinc expands appreciably with changes in temperature. Beads trapped tight between two fixed points will ripple — keep to the usual bay lengths and expansion details. With timber beads, paint the underside and the end grain as well, because that is exactly where the timber draws in water.
Related terms
- Roll moulding
- Beaded matchboarding
- Gutter
- Box gutter
- Sheet metal work
- Drip
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