Truncating is the horizontal cutting off or flattening of the top of a pointed element, such as a roof, tower, pyramid or pier. The result is a flat upper surface instead of a point. A truncated roof has no sharp ridge or spire, but a small flat area at the top.
What does truncating look like?
Imagine a pyramid roof: four sloping surfaces meet at a single point at the top. Truncating removes that point with a horizontal cut, creating a small flat surface. The geometric shape that results is called a frustum (truncated pyramid).
The same principle applies to:
- Towers — a truncated spire has a flat top
- Columns and piers — the top is flattened to form a level bearing surface
- Cones — a truncated cone is flat on top
Application
Truncating occurs in construction at:
- Pyramid roofs — a truncated pyramid roof with a flat centre, sometimes topped with a roof lantern or skylight
- Church towers — historic towers with a truncated spire
- Concrete pad foundations — pad foundations are often truncated pyramids: wide at the base, narrower at the top
- Pier caps — the top of bridge piers is truncated to form the bearing for the deck beams
- Garden design — truncated shapes in hedges and topiary
Why truncate?
- Structural — a flat surface provides a stable bearing point
- Practical — a flat top is easier to waterproof than a point
- Aesthetic — a truncated form can appear more monumental or composed
Related terms
- Roof construction
- Pyramid roof
- Pier
- Pad foundation
- Roof form
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