Christopher alexander - A pattern language

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225 FRAMES as thickened

EDGES**

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. . . assume that columns and beams are in and that you have marked the exact positions of the doors and windows with string or pencil marks—natural doors and windows (221). You are ready to build the frames. Remember that a well made frame needs to be continuous with the surrounding wall, so that it helps the building structurally—efficient structure (206), GRADUAL STIFFENING (208).

The most familiar example of this principle at work is in the human face itself. Both eyes and mouth are surrounded by extra bone and flesh. It is this thickening, around the eyes and mouth, which gives them their character and helps to make them such important parts of human physiognomy.

A building also has its eyes and mouth: the windows and the doors. And following the principle which we observe in nature, almost every building has its windows and doors elaborated, made more special, by just the kind of thickening we see in eyes and mouths.

The fact that openings in naturally occurring membranes are invariably thickened can be easily explained by considering how the lines of force in the membrane must flow around the hole.

T he density of the lines ref resent increasing stress concentrations.

The increasing density of lines of force around the perimeter of the hole requires that additional material be generated there to prevent tearing.

Consider a soap film. When you prick the film, the tension pulls the film apart, and it disintegrates. But if you insert a ring of string into the film, the hole will hold, because the tensile forces which accumulate around the opening can be held by the thicker ring. This is in tension. The same is true for buckling and compression. When a thin plate is functioning in compression and a hole is made in it, the hole needs stiffening. It is important to recognize that this stiffening is not only supporting the opening itself against collapse, but it is taking care of the stresses in the membrane which would normally be distributed in that part of the membrane which is removed. Familiar examples of such stiffening in plates are the lips of steel around the portholes in a ship or in a locomotive cab.

A door frame as a thickening.

The same is true for doors and windows in a building. Where the walls are made of wood planks and lightweight concrete fill—see wall membranes (218)—the thickened frames can be made from the same wood planks, placed to form a bulge, and then filled to be continuous with the wall. If other types of skin are used in the wall membranes, there will be other kinds of thickening: edges formed with chicken wire, burlap, and resin, filled with concrete; edges formed with chicken wire filled with rubble, and then mortar, plaster; edges formed with brick, filled, then plastered.

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More general examples of frames as thickened edges exist all over the world. They include the thickening of the mud around the windows of a mud hut, the use of stone edges to the opening in a brick wall because the stone is stronger, the use of double studs around an opening in stud construction, the extra stone around the windows in a gothic church, the extra weaving round the hole in any basket hut.

Therefore:

Do not consider door and window frames as separate rigid structures which are inserted into holes in walls. Think of them instead as thickenings of the very fabric of the wall itself, made to protect the wall against the concentrations of stress which develop around openings.

In line with this conception, build the frames as thickenings of the wall material, continuous with the wall itself, made of the same materials, and poured, or built up, in a manner which is continuous with the structure of the wall.

In windows, splay the thickening, to create deep reveals (223) ; the form of doors and windows which will fill the frame, is given by the later patterns—windows which open wide (236), SOLID DOORS WITH GLASS (237), SMALL PANES (239). . . .

as you build the main jrame and its openings yput in the following subsidiary patterns where they are appropriate;

226.COLUMN PLACE

227. COLUMN CONNECTION

228. STAIR VAULT

229. DUCT SPACE

230. RADIANT HEAT

231. DORMER WINDOWS

232. ROOF CAPS

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226 COLUMN PLACE*

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. . . certain columns, especially those which are free standing, play an important social role, beyond their structural role as columns at the corners (212). These are, especially, the columns which help to form arcades, galleries, porches, walkways, and outdoor rooms—public outdoor room (69), arcades (lI9), OUTDOOR ROOM (163), GALLERY SURROUND ( 166), SIX-foot balcony (167), trellised walk (174). This pattern defines the character these columns need to make them function socially.

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The fact is, that a free-standing column plays a role in shaping human space. It marks a point. Two or more together define a wall or an enclosure. The main function of the columns, from a human point of view, is to create a space for human activity.

In ancient times, the structural arguments for columns coincided in their implications with the social arguments. Columns made of brick, or stone, or timber were always large and thick. It was easy to make useful space around them.

A big thick column.

But with steel and reinforced concrete, it is possible to make a very slender column; so slender that its social properties disap-

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I I LOCAL TRANSPORT AREAS

treated as a “second vehicle”—and are rather expensive. They make no contribution to the health problem, since people are still sitting motionless while they travel. The system is relatively antisocial, since people are still encapsulated in “bubbles” while they travel. It is highly idealistic, since it works if everyone has a Starrcar, but makes no allowance for the great variety of movement which people actually desire, i.e., bikes, horses, jalopies, old classic cars, family buses.

We propose a system which has the advantages of the Starrcar system but which is more realistic, easier to implement, and, we believe, better adapted to people’s needs. The essence of the system lies in the following two propositions: