Problem
We seek a ceiling vault shape which will support a live load on the floor above, form the ceiling of the room below, and generate as little bending and tension as possible so that compressive materials can be relied on.
Solution
Build floors and ceilings in the form of elliptical vaults, which rise between 13 and 20 percent of the shorter span. Use a type of construction which makes it possible to fit the vault to any shapes room after the walls and columns are in position: on no account use a prefabricated vault.
Related Patterns
… we have already discussed the fact that ordinary joist floors and slab floors are inefficient and wasteful because the tension materials they use to resist bending are less common than pure compression materials - Efficient Structure (206), Good Materials (207), and that it is therefore desirable to use vaults wherever possible. This pattern gives the shape and construction of the vaults. The vaults will help to complete Floor and Ceiling Layout (210), and Perimeter Beams (217); and, most important of all, they will help to create the Ceiling Height Variety (190) in different rooms.
When the main vault is finished, mark the positions of all those columns which will be placed on the floor above it - Final Column Distribution (213) - Whenever there are columns which are more than 2 feet away from the perimeter beam, strengthen the vault with ribs and extra reinforcing to withstand the vertical forces.
Put all the upper columns in position before you pour the floor of the vault, so that when you pour it, the concrete will pour around the column feet, and anchor them firmly in the same way that they are anchored in the foundations - Root Foundations (214).
To finish the under surface of the vault paint it or plaster it - Soft Inside Walls (235). As for the floor surface above, either wax it and polish it or cover it with soft materials - Floor Surface (233)
Alexander, Christopher. A Pattern Language: Towns, Buildings, Construction. Oxford University Press, 1977, p. 1027.