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This wall is solid (about the density of wood), has good acoustic and thermal properties, can easily be built to conform to free and irregular plans, and can be nailed into. And because of its stiffeners, the wall is very strong for its thickness.

Other versions of this pattern: (i) The skin can be formed from hollow structural tiles or concrete blocks, with a concrete or earthen fill. (2) The exterior skin might be brick, the interior skin plywood or gypboard. In either case the columns would have to be hollow tile, or concrete pipe, or other masonry box columns. (3) The skin might be formed with wire mesh, gradually filled with concrete and rubble, and stuccoed on the outside, with plaster on the inside. The columns in this case can be built in the same way—out of a wire mesh tube filled with rubble and concrete. (4) It may also be possible to use gypboard for both skins, inside and out. The gypboard on the outer side could then be covered with building paper, lath, and stucco.

Therefore:

Build the wall as a membrane which connects the columns and door frames and windows frames and is, at least in part, continuous with them. To build the wall, first put up an inner and an outer membrane, which can function as a finished surface; then pour the fill into the wall.

I I LOCAL TRANSPORT AREAS**
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CONSTRUCTION

inner and outer membrane

Remember that in a stiffened wall, the membranes can be much thinner than you might expect, because the stiffeners prevent buckling. In some cases they can be as thin as two inches in a one story building, three inches at the bottom of a two-story building and so on—see final column distribution (213).

Membranes can be made from hollow tile, lightweight concrete block, plywood, gypboard, wood planks, or any other sheet type material which would make a nice surface, which is easy to nail into, comfortable to touch, and so on. If the inner sheet is gypsum board, it can be finished with a skim coat of plaster—soft inside walls (235). The outer sheet can be made of 1 inch boards, tongue and grooved; or exterior grade plywood; or exterior board hung with tile, shingles, or plastered—lapped outside walls (234). It is also possible to build the outer skin of brick or tile: in this case, columns must be of the same material—soft tile and brick (248). . . .

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219 FLOOR-CEILING VAULTS**

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. . . 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.

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.

The vault shape is governed by two constraints: the ceiling cannot be lower than about 6 feet at the edge of the room, except in occasional attic rooms; and the ceiling in the middle of the room should vary with the room size (8 to 12 feet for large rooms, 7 to 9 feet for middle sized rooms, and 6 to 7 feet for the very smallest alcoves and corners—see ceiling height variety (190)).

We know, from structural considerations, that a circular shell dome will generate virtually no bending moments when its rise is at least 13 to 20 per cent of its diameter. (This is established in studies and tests of shell structures, and is corroborated by our own computer studies.) For a room 8 feet across, this requires a rise of about 18 inches, making a total height of 7 to 8 feet in the middle; for a room 15 feet across, it requires a rise of 2-3 feet, making a height of 8 to 10 feet in the middle.

Luckily, these vault heights are just congruent with the needed ceiling heights. We may say, therefore, that the ideal vault for an inhabited space is one which springs from 6 to 7 feet at the edge, and rises 13 to 20 per cent of the smaller diameter.

1028 219 FLOOR-CEILING VAULTS

There are various possible ways of making a circular or elliptical vault spring from a square or rectangular room.

I. One type of vault is made by arching diagonal ribs from corner to corner; and then spacing straight line elements across the ribs.

2. Another type is a pure dome supported on squinches.

3. Another is based on a rectangular grid of arched ribs. The edge ribs are entirely flat, and the center ribs have the greatest curvature. In the end, each part of the vault is curved in three dimensions, and the corners are slightly flattened.

Each of these three vaults makes sense in slightly different circumstances. The first is the easiest to conceive, but it has a slight structural disadvantage: its surface panels are curved in one direction only—because they are made of straight line elements —and cannot therefore achieve the strength of a doubly curved vault. The second is the hardest to conceive; however, it comes naturally from the intersection of a spherical shape and a rectangular one. If one were to make a vault by using a balloon as a form, pushed up within the perimeter beams, the second type would be the easiest to use. In the particular building technique we have been using, the third type is easiest to use, because it is particularly

CONSTRUCTION

simple to lay out the arched ribs which provide the formwork. It flattens out at the coiners, which could create bending moments and require tension materials. However, in lightweight concrete we have found that it docs not require any more than the shrinkage reinforcement, which is needed anyway.

Wc shall now describe a very simple way of making a vault. Bear in mind that wc considered it essential that the vault be built up gradually, and that it could be fitted to any room shape, without difficulty. This technique is not only cheap and simple. It is also one of the only ways wc have found of fitting a vault to an arbitrary room shape. It works for rectangular rooms, rooms that are just oft-rectangles, and odd-shaped rooms. It can be applied to rooms of any size. The height of the vault can be varied according to its position in the overall array of ceiling heights and floors—ceiling height variety (190), structure

FOLLOWS SOCIAL SPACES (2O5), FLOOR AND CEILING LAYOUT (210).

First, place lattice strips at one foot centers, spanning in one direction, from one perimeter beam to the opposite perimeter beam, bending each strip to make a sensible vault shape. Now-weave strips in the other direction, also at almost one foot centers, to form a basket. The strips can be nailed onto the form of the perimeter beam around the room. You will find that the basket is immensely strong and stable.

Lattice strips in position.

Now stretch burlap over the lattice strips, tacking it on the strips so it fits tightly. Paint the burlap with a heavy coat of polyester resin to stiffen it.

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219 FLOOR-CEILING vaults
Burlap over the lattice work.

The burlap-resin skin is strong enough to support I to 2 inches of lightweight concrete. In preparation for this, put a layer of chickenwire, as shrinkage reinforcement, over the stiffened burlap. Then trowel on a 1- to 2-inch layer of lightweight concrete. Once again, use the ultra-lightweight 40-60 pound concrete described in GOOD MATERIALS (2O7).