Stair Vault

… this pattern helps complete the rough shape and location of stairs given by Staircase As A Stage and by Staircase Volume. 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, without using wood or steel or concrete - Good Materials?

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.

Therefore:

Build a curved diagonal vault in the same way that you build your Floor-ceiling Vaults. Once the vault hardens, cover it with steps of lightweight concrete, trowel-formed into position.

A concrete stair is usually made from precast pieces supported by steel stringers; or it is formed in place, and then stripped of its forms. But for the reasons already given in Good Materials, precast concrete and steel are undesirable materials to use - they call for modular planning; they are unpleasant materials to touch, look at, and walk on; they are hard to work with and modify in any relaxed way, since they call for special tools.

Given the principles of Efficient Structure, Good Materials, and Gradual Stiffening, we suggest that stairs be made like Floor-ceiling Vaults - by making a half-vault (to the slope of the stair), with lattice strips, burlap, resin, chickenwire, and lightweight concrete. The steps themselves can then be formed by using wood planks, or tiles, as risers, and filling in the steps with trowelled concrete.

When we first wrote this pattern, we thought it was very doubtful - and put it in mainly to be consistent with floor and roof vaults. Since then we have built a vaulted stair. It is a great success - beautiful - and we recommend it heartily.

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