### Problem
>Within a building technology which uses compressive materials as much as possible, and excludes the use of wood, it is natural to build stairs over a vaulted void, simply to save weight and materials.

### Solution
>Build a curved diagonal vault in the same way that you build your [[Floor-Ceiling Vaults (219)]]. Once the vault hardens, cover it with steps of lightweight concrete, trowel-formed into position.

### Related Patterns
... this pattern helps complete the rough shape and location of stairs given by [[Staircase as a Stage (133)]] and by [[Staircase Volume (195)]]. If you want to build a conventional stair, you can find what you need in any handbook. But how to build a stair in a way which is consistent with the compressive structure of [[Efficient Structure (206)]], without using wood or steel or concrete - [[Good Materials (207)]]?

A lightweight concrete tread, colored, waxed, and polished can be quite beautiful and soft enough to be comfortable - see [[Floor Surface (233)]] - and will eventually take on the patina of wear called for in [[Soft Tile and Brick (248)]].

The vaulted space under the stair can be used as an [[Alcoves (179)]], a [[Child Caves (203)]], or [[Closets Between Rooms (198)]]. If it is plastered, like a regular ceiling - see [[Floor-Ceiling Vaults (219)]], it makes a much more pleasant and useful space than the space under an ordinary stair.

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> [!cite]- Alexander, Christopher. _A Pattern Language: Towns, Buildings, Construction_. Oxford University Press, 1977, p. 1073.
> #APL/confidence/medium
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> #APL/Construction-Patterns/Frame-Adjustments