In building, a collar is any component shaped like a collar: a ring or sleeve that closes around something else. In Dutch practice the word is also used specifically for the centre of a spiral stair — the column the treads turn around.
1. The collar as a ring-shaped component
Wherever a round or square element passes through a building element, a collar seals or finishes the junction:
- Around a roof penetration — the lead, EPDM or plastic sleeve around a soil vent pipe, with a flange that runs under the roof covering.
- Around a chimney — the lead or metal flashing set as a collar around the flue and discharging onto the roof covering.
- Around services through a wall or floor — a plate or sleeve closing the opening; at a fire compartment wall, an intumescent collar that swells shut in a fire.
- In the facade — a projecting ring or band finishing a column or a chimney stack.
The rule is the same in every case: the collar must sit over the water-shedding surface, never under it, so water always runs across it rather than behind it.
2. The collar as the centre column of a spiral stair
In a spiral stair, the collar is the central column the treads are fixed into — also called the newel or the spindle. Structurally it is the most important part of the stair: it carries every tread, and every tread applies a twisting moment to it.
Points to watch:
- The column has to be firmly anchored at its base; a spiral stair stands or falls on that fixing.
- The treads are usually stacked on the column with spacer sleeves, which sets the riser height exactly.
- Going and rise vary across the width of a spiral stair, so comfort is judged on the walking line, not at the column.
Related terms
- Spiral stair
- Newel
- Roof penetration
- Lead flashing
- Chimney
- Going
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