A classification of built forms

IntroductionA national Non-Domestic Building Stock (NDBS) database has been developed forthe Department of Environment, Transport and the Regions (Steadman et al, 2000a).In this database the activities in buildings and the geometrical forms of buildings havebeen classified separately. The reasons for making this distinction are set out in Bruhnset al (2000). They have to do with the very loose relationship of form to function in theexisting building stock. A single, readily distinguishable type of built form such as thatof a converted terrace house, or a prefabricated shed, can house any of a very widerange of activities. Conversely, the same activity, for example office work, can becarried on in any of a number of different geometrical forms of building. In the presentpaper we describe the classification of built formsöindependent of the uses to whichthey are putöwhich has been developed for the NDBS database.

The classification has been based on the empirical evidence of buildings surveyedat 3350 addresses in four English towns (Brown et al, 2000), as represented in pseudo-three-dimensional form in the Smallworld GIS (Holtier et al, 2000). Special attentionwas given to the buildings covered in the Swindon survey. Some 400 of these weredrawn in axonometric projection at a standard scale, and measurements were made.Figure 1 (see over), illustrates sample drawings of medium-sized shops, schools, andindustrial sheds in Swindon. Some standard books on building types were also con-sulted, for example Clay (1902) and the Department of Education and Science and theWelsh Office (1977) on school buildings, Joedicke (1962) on offices, Ham (1972) ontheatres, Klose (1965) on multistorey car parks and garages, and others. Because somany nondomestic activities are found in converted houses, it was also possible tomake use of earlier work on the systematic classification of house forms in the Englishstock (Brown and Steadman, 1991a; 1991b).

A classification of built forms

Philip Steadman}, Harry R Bruhns}, Senino Holtier, Bratislav GakovicDepartment of Design and Innovation, Faculty of Technology, The Open University,Walton Hall,Milton Keynes, England

Peter A RickabyRickaby Thompson Associates Ltd, Witan Court, 296 Witan Gate West, Central Milton KeynesMK9 1EJ, England; e-mail: [email protected]

Frank E BrownThe Manchester School of Architecture, University of Manchester, Manchester, England;e-mail: [email protected] 8 April 1999

Environment and Planning B: Planning and Design 2000, volume 27, pages 73 ^ 91

Abstract. A classification of built forms is presented. It is based on a study of buildings surveyed at3350 addresses in four English towns and has been designed for use in the national Non-DomesticBuilding Stock (NDBS) database developed for the Department of Environment, Transport and theRegions. As the prime use of the database is in energy analysis, the classification focuses on theexternal envelopes of buildings. (Materials of construction, servicing systems, and activities areclassified separately.) Built forms are distinguished according to two main criteria: the broad `texture'of their internal subdivision; and whether they are daylit or artificially lit.

}Current address: The Bartlett School of Graduate Studies, University College London, GowerStreet, London WC1E 6BT; e-mails: [email protected]; [email protected]

DOI:10.1068/bst7

mailto:[email protected]




(a)

(b)

Figure 1. Examples of (a) medium-sized shops, (b) schools, and(c) industrial sheds in Swindon,drawn in axonometric views at ascale of approximately 1:1300.

74 J P Steadman, H R Bruhns, P A Rickaby, F E Brown, S Holtier, B Gakovic

Some simplifying strategiesThree strategies have been adopted to simplify the representation of built form, for thepurposes of developing a comprehensive classification. First, all minor details offormöany surface articulation, attached orders, small porticoes and balconies, smallbay windows and dormers, etcöare ignored. Clearly this requires judgment as towhich details can be regarded as `minor' in this context. Experience in applying theclassification has shown that some sensible dividing lines can be drawn in practice.

Second, buildings of complicated form are broken down into smaller componentparts and these parts classified separately, where necessary. We will show exampleslater. The decomposition also separates what we have called primary forms fromsmaller subsidiary or attached elements, referred to here as parasites. This distinctionis also explained in more detail below.

Third, a conceptual separation is made between the dimensions of a built form,and its shape or configuration. That is to say, the forms are represented parametrically.In the example of the simple `shed' (rectangular plan, double-pitched roof with gables)this can be described adequately by associating four dimensional parameters to thebasic form: plan dimensions of length and width, height to eaves, and roof slope

(c) Figure 1 (continued).

A classification of built forms 75

(or height to ridge) (figure 2). These parameters measure continuously variable quan-tities. In other instances parameters might take integral values, for example to describenumbers of floor levels. Such an approach to representation means that a singlecanonical `dimensionless' built form can stand, in principle, for an infinitely large classof dimensioned instances.

(In the event, there proved to be both practical and conceptual difficulties inmaking automatic measurements of the plan dimensions of length and depth of thebuilt forms surveyed in the four towns. Values have been determined only for param-eters defining numbers of storeys, storey heights, floor areas on each floor level, androof slopes for different geometrical forms of roof. In addition, the total length ofexternal wall has been measured for each form. When considered in combination,however, the values for floor area on a given level, and total external wall length onthat level, have some implications for plan shape and plan depth.)

The orthogonal geometry of buildings in planIn the classification of forms it is assumed that, for the most part, the external geometryof buildings in plan is orthogonal. That is to say, the outside walls of each building are ineffect aligned in plan on a rectangular coordinate system, and all corners formed bythose walls are right angles. This assumption is supported by evidence from severalsurveys (see Bemis, 1936; Kru« ger, 1977) besides those in the four towns. Minor depar-tures from plan orthogonality, such as curved or angled bay windows, or rounded orchamfered corners, are ignored. In cases where plan shapes approximate to orthogon-ality but the angles between walls depart slightly from 908öas in many old buildings, orbecause of the exigencies of sitesöthose plans are treated as if perfectly rectangular.

There are three other sets of circumstances where buildings can typically depart inplan from orthogonality. The first is where a number of rectangular building masses ofa linear characteröfor example, the blocks or wings of a large office or institutionalbuildingöare joined at angles other than 908 by nonrectangular linking elements,typically containing circulation space or services. The second is where an elongatedslab or `strip' building is given a gently curving plan, but an approximation toorthogonality is nevertheless preserved at the local scaleöas in a crescent of terracedhouses. The third is in the plans of buildings which consist of single spaces, forexample open-plan single-storey industrial premises, or detached chapels, bandstandsor kiosks. Here the plan shape as a whole may be polygonal (either regular orirregular), perhaps even circular or elliptical. All such cases are catered for in theclassification which follows.

h

lw

a

Figure 2. A simple `shed' form described by four parameters: length, l; width, w; height, h; roofslope, a.


In the vertical direction the principal departure of the geometry of buildings fromthe orthogonal tends to be in the form of pitched roofs. Several different forms ofsloping roof are allowed for, with any angle of slope.

Basic criteria for classification: (1) daylit and artificially lit spaceWe draw some very broad distinctions between certain basic properties of built space.The first is between space which is daylit and space which is artificially lit. In buildingswith orthogonal geometry, daylight can enter from the side, via windows; or, in thetopmost storey only, from above, via rooflights. Exactly how far daylight can enterhorizontally through windows is in practice determined by many complicating factors:floor-to-ceiling height, area and type of glazing, the sizes and positions of any externalobstructions, etc. One very important consideration is what actual level of daylightingis considered acceptable in the worst case.

In principle, however, we can say that constraints of daylighting must put aneffective limit on the maximum allowable depth of sidelit space away from the win-dows. Beyond this limit, permanent artificial lighting of some kind is required. In somebuildings there are daylit (sidelit) rooms on the periphery, and artificially lit rooms inthe interior; in this case the boundary between the two types of space is clear-cut. Inbuildings with open plans, such a boundary cannot be absolutely fixed by theoreticalconsiderations alone. But empirical data from a sample of such buildings would showthe range of values the limit of daylighting tends to take in practice.

This distinction between daylit and artificially lit space is obviously a very relevantone from an energy point of view: not just because of the use of energy in artificiallighting, but also because of the relationship with plan depth, which can in turn affectdemands for heating, cooling, and mechanical ventilation. Figure 3 gives some statis-tics for plan depth in nineteen large purpose built office buildings in Swindon. Thegraph shows total floor area (square metres) in slabs or `strips' of the specified depth(metres). The distribution is bimodal, with one group of buildings, clustered around14m in depth, in which the space is wholly daylit and has the potential to be naturallyventilated; and a second group, in the range 18 to 22m, in which the space is morelikely to require air conditioning. These figures accord with the norms applied inpractice for maximum daylit depths in offices. The LT method for energy design (forexample, Baker et al, 1994) sets a depth of 6m for the peripheral `passive' zones in a plan

60 000

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area,m

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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24Depth, m

Figure 3. Plan depths of nineteen large purpose-built office buildings in Swindon. The graphshows total floor area (square metres) in slabs or `strips' of the specified depth (metres).


which can be naturally lit (assuming the ceiling height to be 3m). For a double-aspect,wholly daylit plan with a central corridor of, say, 2m width this would give a totaldepth of 6� 6� 4 � 14m. It is clearly important for a classification for energy analysisto distinguish these respective types of form.

Basic criteria for classification: (2) the average sizes of roomsOur second distinction has to do with the sizes in plans of rooms or other enclosedspaces. In theory, rooms might take any plan dimensions, with a lower limit on area ofperhaps a square metre, and no effective upper limit other than that imposed byconsiderations of cost and access. In practice, however, we observe that rooms taketypical ranges of size, depending on their functions and on the possibilities allowed bythe structural systems and materials from which they are built. Thus empirical studiesof room sizes in houses and flats show that `habitable' rooms such as living rooms,dining rooms, kitchens, and bedrooms take restricted ranges of values for floor area,with distributions which are in general strongly peaked (Brown and Steadman, 1991a).(This evidence does not imply that other sizes outside these ranges are impossible inhouses, only that they are rare.)

We might expect the same to apply to individual offices in commercial officebuildings, to bedrooms in hotels, to classrooms in schools, and so on. Such roomsserve relatively standardised purposes, are equipped and furnished in broadly similarways, and accommodate roughly comparable numbers of occupants. The actual sizes,on average, of these cellular rooms, when they are sidelit, can again have a constrain-ing effect on the depths of buildings in plan. Thus cellular space for domestic usewould tend, in general, to be less deep in plan than cellular office space. Figure 4 givesstatistics for plan depth in a random sample of terraced and semidetached houses inCambridge, reproduced from Brown and Steadman (1991a). The numbers of houseswith different depths are given in each case. `Back extensions' have been ignored in themeasurements. In both types of house, the depth values are strongly clustered about amean of just over 7m. Comparison with the statistics for office buildings in figure 3shows that these results must be due to the typical sizes of rooms in houses, and notany ultimate limits on depth set by the demand for sidelighting as in the offices.

Rooms of this cellular type can occur in isolation. A detached building mayconsist, on one floor level, of a single living room, a single small office or a singleclassroom. But it is frequently the case in practice that such rooms are assembledtogether repetitively in groups: domestic rooms into houses, hotels or hospital wards,office rooms into office towers, classrooms into classroom blocks. We refer to thesekinds of assemblies of approximately similar-sized rooms as cellular space. (It isassumed that forms which for the most part make up cellular space will also contain

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01 2 3 4 5 6 7 8 9 10 11 12 13 1 2 3 4 5 6 7 8 9 10 11 12 13

Depth, m Depth, m

Figure 4. Plan depths of samples of terraced and semidetached houses in Cambridge. (`Backextensions' are ignored in the measurements.) The graphs show numbers of houses of thespecified depth (metres).


circulation areas, stores, toilets, and other small `servant spaces', many of which mightbe artificially lit.) It might be better to speak of cellular space being characterised, notso much by the specific sizes of its component rooms as by a certain broad `texture ofspatial subdivision'.

Moving to larger sizes of room, there would be typical ranges of plan dimension forsuch specialised spaces as lecture theatres, assembly halls, churches and chapels, court-rooms, conference chambers, cinemas, theatres, and other auditoria. In each case, thespace is occupied by a single coordinated activityöassembly, performance, meetingöwhich demands a coherent unobstructed volume. The plan shape and height relative tothe plan dimensions are constrained, if loosely in some cases, by the demands ofvisibility of one small areaöthe stage, screen, lectern or altaröfrom every other point.We have called all these kinds of spaces halls. They may in some cases be repeated incontiguous groups (as in multiscreen cinemas, or lecture theatre blocks in colleges) butit is more usual for them to be found singly.

A third category of built space can be described by the term open plan. Here thespace continues unobstructed by walls, across what is in principle an unlimited extentof floor area. Where the occupants of a hall are, broadly speaking, all engaged in oneunified event, the occupants of open-plan space are busy in many separate activitiesöthough all perhaps serving some common purpose at a higher level. Most usually it isoffice space of this character which is referred to as open plan. But, in the character-isation of built form, the same description can be applied to many large shops and tocertain kinds of industrial building such as warehouses and mills. Where open-planaccommodation is provided on multiple floor levels, it consists typically of extendedhorizontal `slices' of space with constant floor-to-ceiling height. Where it occurs atground level only, as in many modern factories, warehouses, and supermarkets, thenit may be provided in forms with many different types of structural system and roofgeometry, often in assemblies of adjacent `sheds', and often toplit by rooflights ormonitors.

Combinations of lighting and room size categoriesIn summary, then, our three categories of built space related to typical room size are:cellular space, halls, and open-plan space. We can permute these with our two lightingcategories, to create six possibilities:(1) Daylit cellular;(2) Artificially lit cellular;(3) Daylit hall;(4) Artificially lit hall;(5) Daylit open plan;(6) Artificially lit open plan.The categories are intended, as explained, to begin to make geometrical distinctionsbetween built forms. The six types of space are nevertheless best characterised by theirrespective abilities to accommodate different `generic functions' and can be explainedby reference to the ranges of specific activities which would tend to be found in them.Daylit cellular would include most domestic space in houses or flats, as well as buildingsof a similar geometrical and constructional character used for a variety of nondomesticuses. It would include much of the space in hotels and public houses. And it would alsocover most office accommodation, with the obvious exception of open-plan offices.

The daylighting in the great majority of such cases would be by sidelighting becauseit would generally be regarded as desirable for rooms with all these functions to haveviews. This is not to deny that windowless small offices and even windowless hotelrooms exist, just to emphasise that they are rare. The permutation artificially lit cellular


is thus architecturally somewhat improbable, although it can occur in basements. Toplitcellular space is found on occasion in changing rooms and public baths.

Halls may be daylit from the side, as typically in churches, or from the top, as inmany courtrooms. The category artificially lit hall would account for all cinemas,theatres, and television studios.

Daylit open plan implies either that the space is toplit and is thus single storey orthe topmost of several storeys; or, if it is sidelit, that it does not exceed the maximumdepth in plan for this to be feasible. Artificially lit open plan has no such restrictionsand can be extended indefinitely in the horizontal plane, and superimposed on anynumber of storeys. It is worth noting that, although the great majority of shops havelarge windows on the street frontage, these do not in many cases actually admitdaylight to the interior but are wholly blocked by merchandise and displays. Space insuch buildings is thus properly included under the artificially lit open-plan category.Some large modern warehouses have no daylight and would also fall into this group, aswould below-ground car parks.

The constraints of sidelighting: `strips' of sidelit spaceIf an extent of floor space is to be completely sidelit, then the walls in which thewindows are set must obviously not be obstructed externally, and the plan must notexceed the relevant limit on depth. It follows that, as the area of that floor spacebecomes larger, so the shape of the building mass must become elongated in eitherthe horizontal or the vertical direction, or both, to prevent the depth limit beingbroken. Where sidelit facades on two building masses face each other, they must bekept a suitable distance apart. We have used the term sidelit strips to refer to thegeneral class of forms resulting from such constraints. Some sidelit strips derive theirlight from one side only, but usually they are lit from the two opposite sides, in whichcase the maximum plan depth is of course twice as great. (Perhaps slightly less thantwice in practice, if the width of a corridor is included in both cases.)

A sidelit strip may extend indefinitely in plan in a straight line. There are manyactual buildings, composed of space of this type, which do indeed take the form ofsimple long straight slabs. We have already mentioned the alternative possibility ofsidelit strips taking gradually curving shapes in plan, as in crescents or sinuous snakingoffice buildings. In other cases, lengths of sidelit strip are in effect cut and joined tocreate more complex plan shapes, as for example L, T, E, F, H, U, or courtyard forms, allof which are common among larger office buildings, schools, hotels, and apartmentbuildings. The lengths of the component strips, and the dimensions of courtyards, canbe varied ad lib, so long as opposing window walls are separated by sufficient distancesto preserve daylighting. As the number of storeys is increased (assuming a fixed storeyheight, and other things being equal), so this separation distance must be made greater,if daylighting standards are to be maintained. This applies to daylit facades where theybelong either to the same building, or to separate but neighbouring buildings. March(1972) developed a theoretical model of the effects of such constraints on built form.

The question arises whether from an energy point of view, and for the classificatorypurposes of the NDBS database, it is important to capture such differences in overallplan shape created by the assembly of sidelit strips in various arrangements. Does thefact that a plan shape is formed from a series of courtyards, for example, as opposed tolinear slabs or free-standing towers, resultöother things being equalöin reducedstandards of daylighting, say, and thus in a significantly increased use of electricityfor lighting? Does it result in reduced solar gains because of overshadowing in thecourtyards? Is the orientation of facades important, or can this be treated as effectivelyrandom for analytical purposes, when large numbers of buildings are considered


together, with approximately equal areas of sidelit facade being exposed to all points ofthe compass? All these are empirical questions, to which some answers might be foundfrom energy surveys of actual buildings, or through simulation.

A rough-and-ready system of letter codes has been used to make crude descriptionsof the plan shapes of all built forms covered in the four surveys. In practice, however,these have not been used, and the principal system of classification simply distinguishesforms as being composed of sidelit strips and otherwise ignores plan configuration.(The fact that total external wall length is measured accurately for every form never-theless means that some effects of the lengths, bends, and junctions of strips are takeninto account.)

Composite assemblies of built formsWe have already introduced the idea that buildings of complex form are to be decom-posed, for the purposes of classification, into separate built form components, where thesecomponents may possibly be assigned to different classificatory categories. Figure 5(a)illustrates, for example, the 19th century public baths in Swindon, still in use today as ahealth centre. The plan is complex; indeed it is difficult to understand even from detaileddrawings. One of its oddest features is a c̀rack' in the basic rectangular layoutöa sort ofalley, open to the skyövisible at bottom right in the drawing.

The overall form may nevertheless be decomposed into a number of simplercomponents, as in figure 5(b). Here it is easy to pick out four toplit halls, two ofthem containing swimming pools (centre and lower left) and two for other uses. Thereis some toplit and artificially lit cellular space accommodating Turkish baths. Other-wise the building consists largely of cellular office space, lit mostly from one side only,the bulk of it in an L-shaped `strip' along two outer edges of the plan. The presentclassification would categorise these various component forms separately and preserve

(a)

(b)

Figure 5. (a) The complex form of the 19th century public baths in Swindon, and (b) this formdecomposed into simple built form elements.


little or nothing of the spatial relationships in which they are assembled, again on theassumption thatöto a first order of approximationösuch relations are not significantfor energy use. [The fact that some of the built form components are contiguous andshare internal wallsöshown shaded in figure 5(b)öis nonetheless allowed for in thecalculation of external wall lengths and areas. Only walls which are genuinely exposedare counted, as explained in Holtier et al (2000).]

As the classification scheme applies only at the level of component forms, and theprecise spatial configurations in which these are arranged are (with a few exceptions)ignored, we need not be greatly concerned with these composite assemblies as such.Just for the sake of illustration, however, figures 6 to 11 show in schematic form just afew of the more common ways in which built form components are found in combina-tion in the existing building stock. It should be emphasised that these compositeassemblies do not in themselves correspond to categories in the classification scheme.Nor is this anything more than an arbitrary selection of a few possibilities. [A techniquefor representation which could allow complex built form assemblies to be described andenumerated in more systematic and quantified fashion is outlined in Steadman (1998).]

Daylit cellular space may be placed on top of lower floors consisting of artificially litopen plan space. Such combinations are frequently seen in buildings in which offices orflats are provided above large shops. Figure 6 shows a typical case, filling the entirewidth of a site fronting, say, onto a commercial high street. The end walls are thus partywalls. Two shop floors fill the complete site at ground and first-floor levels. A daylitdouble-aspect strip of office accommodation is then placed on the street frontage atsecond and successive floor levels. Clearly, other positions and arrangements of sidelitstrips on top of open-plan space are possible within the constraints of daylighting.

Further possibilities for composite assemblies arise by the placing of differentcategories of space side by side (as in the Swindon public baths). A hybrid arrangementof this kind which often occurs in practice is one where rectangular halls are surrounded,perhaps on all sides, by single-aspect sidelit strips (figure 7). The halls can be sidelit fromany exposed sides, lit by clerestories, or toplit if they are completely surrounded. It may bethat the halls are of sufficient storey height that they are equal in height to two or morefloors of the surrounding daylit strips. Actual examples of such arrangements are to befound in court buildings (courtrooms surrounded by cellular offices), theatres (theauditorium surrounded by foyers, bars, greenrooms, etc) or buildings for sports suchas gymnasia or swimming pools.

Another possible type of combination is for single-aspect sidelit strips to be setalong some or all of the outer edges of an open-plan space, or around the outside of

Figure 6. Schematic terraced building consisting of daylit cellularspace above artificially lit open-plan space.


artificially lit cellular space (figure 8). Thus daylit offices may be arranged along thesides of a large shop, especially on upper floors. Or individual cellular offices may beplaced around the outer edges of a very deep office floor, whereas uses not requiringdaylightöcomputer rooms, post rooms, telephone relay rooms, etcöare grouped inthe interior. [This is equivalent to what Joedicke (1962) calls a `triple zone' office plan.]Sidelit strips can be combined with open-plan space devoted to industrial uses, as inthe classic small factory or garage, consisting of a `front office' and an adjoining shedor sheds behind (figure 9). Another typical arrangement in factories or warehouses isfor a single-aspect strip of cellular space, on one or more storeys, to be created insideshed, along one or more of its sides, the remainder of the shed being given over toopen-plan space. (This particular situation is so common that we have, for conveni-ence, given it a special classificatory category as a c̀omposite' form.)

It is possible for halls to be incorporated within systems of courts which otherwiseconsist of daylit strips. This arrangement is often found in schools, where the assemblyhall, dining room, or gymnasium is integrated within a courtyard pattern of classroomsand staff offices. In the headquarters of a local authority, say, a debating chambermight similarly be embedded in what is otherwise a sidelit cellular office complex(figure 10). One familiar composite form, which combines the different categories of

Figure 7. Schematic building consisting of a hall surrounded bysingle-aspect daylit cellular space.

Figure 8. Schematic building consisting of single-aspect daylitcellular space set along the edge of artificially lit open-plan space.

Figure 9. Schematic building consisting of single-aspect daylit cellularspace adjoining an open-plan shed.


space in both the horizontal and the vertical directions, is the `slab-on-podium' officebuilding (figure 11). Here the podium, of perhaps two or three storeys, consists of asingle-aspect sidelit strip around a central core of artificially lit space; the slab on top ispure double-aspect sidelit space.

Small single-room forms`Cellular space' and `open-plan space' (whether daylit or artificially lit) are descriptionswhich make sense only as distinct categories when the total area of floor space is large.Consider a building consisting on each floor level of a single room on the scale of adomestic living room, a school classroom, or an office for one or two persons. Is thiscellular space or open-plan space? It is not really either, because there is no repetition ofc̀ells' and the extent of the plan is not great enough to call it `open'. We need a way ofcategorising these `single-room forms'öthat is, forms with one principal room perflooröwhich distinguishes them, essentially by size, from isolated halls, because thereare large numbers of them in the nondomestic stock. In terms of activities, they includesmall free-standing shops and kiosks, single offices in temporary structures such as sitehuts and `portakabins', garages for one or two cars, and detached public lavatories.

Figure 10. Schematic building consisting of a hallembedded in courts composed of double-aspect daylitcellular space.

Figure 11. Schematic `slab-on-podium' building. Thepodium consists of single-aspect cellular space sur-rounding artificially lit space. The slab is made up ofdouble-aspect daylit cellular space.


As mentioned earlier, because these forms when detached are free from the constraintsof close-packing in the horizontal plane, their plan shapes may often depart fromorthogonality.

A system for classifying built formsWe are now in a position to present the system for classifying built forms, based on theprinciples already outlined. A basic distinction is drawn between what have been termedprincipal forms and parasitic forms. The principal forms can be classified in terms of thesix basic categories of space, with variants, as described. There may be other minor builtform elements, however, attached around the periphery, or sitting on the roof, which donot fall easily into this six-way classification. If such elements are very minor in scalethey can safely be ignored. But where they account for significant amounts of floorspace, and especially if that floor space is heated or otherwise serviced, they oughtarguably to be included in the classification of forms. We are referring here to sucharchitectural entities as large porches, lean-to extensions (including lean-to conserva-tories), portes cocheres or canopies (including canopies over loading bays or over thepumps of petrol stations). None of these would be found in isolation, as buildings intheir own right. They exist always as additions to other structuresöhence the term`parasitic'.

The examples just cited are all elements which would necessarily be attachedaround a principal built form at ground (or entrance) level only. Further examples ofparasitic built forms are to be found in those multistorey buildings where the verticalcirculation is removed from the main building masses and is provided in separatetowers attached to the sides or ends of those masses. Where such a building is flat-roofed, the lift machinery and other plant may be housed in a distinct structure orstructures on the roof. (In other cases, both vertical circulation and plant may verywell be incorporated within the principal forms.)

We will provide a full classification of parasitic forms shortly. Table 1 lists thecategories for principal built forms, together with an indicationöfor explanation andguidance only, and not by any means forming a part of the classification itselföas tothe typical range of activities found in each type of space. Figure 12 (see over) showsthe categories diagrammatically. The drawings should be read in every case as para-meterised descriptions. All plan areas, numbers of storeys, roof slopes, etc are to beunderstood as variables (although in some cases with restricted ranges).

The sidelit strip forms are shown as straight lengths, of constant depth, whereactual buildings might consist of multiple strips, of varying depth, even curved inplan, assembled into complex plan configurations as already described. Artificially litforms have no theoretical limits on their depths in plan. They are illustrated here withsimple rectangular plans, although in reality their plan shapes could be many andvarious. Again, the indication of the roof forms is quite schematic. Each built formcategory might be associated with any of a variety of forms of roof. The original codingof the data from the four towns recorded actual roof geometry and angles of roof slopein some detail (Brown et al, 2000). That coding is therefore not duplicated in thepresent system.

Some comments are in order, on individual codes. For convenience, the respectivecategories for sidelit strips, both cellular (CS) and open plan (OD), have been sub-divided into forms with between one and four storeys (CS4, OD4) and forms with fivestoreys and more (CS5, OD5). This corresponds broadlyöalthough not in everyinstanceöto a distinction between forms in which staircase access alone is possibleand forms for which lifts are necessary.


Open-plan space other than sidelit has been divided into a number of subcatego-ries, based on properties of form which have essentially to do with structural systems.[Whether built forms have framed or load-bearing construction is nevertheless classi-fied separately in the NDBS database (Brown et al, 2000).] Thus `open-plan space in asingle shed' (OS) is distinguished from `open-plan continuous single-storey space'(OC1) which would be provided typically in framed structures without internal parti-tions and roofed with monitors or multiple pitched roofs. The separate category for c̀arparking and trucking decks' (OG) is the one case in which we break our self-imposedrule of separating activity from built form in the process of classification. This isbecause of their very distinctive form of construction, their access ramps, low ceilingsand possibly sloping floors, and the fact that as a consequence such space is mostunlikely to be converted to other uses. Some categories specify whether daylit formsare sidelit or toplit or both. (Although in practice it was not always resolved, fromstreet surveys alone, whether built forms in the four towns were in fact toplit, or litwholly by artificial light. Some categories therefore allow for this uncertainty.)

A category is allowed for `single-room forms' (SR) and another for `strings ofsingle-room forms' (SSR). The latter might seem like another way of referring to asidelit strip, and indeed the distinction is not absolutely clear-cut. The SSR category isused, however, in those cases, typically in factory complexes and depots, where a seriesof contiguous but structurally separate small huts or stores or offices have been strungalong an access road or the edge of a site. Each is entered separately from the exteriorand there is no continuous internal circulation. A separate code (RA) is allowed forarches in railway viaducts converted to useable accommodation because of theirspecial structural and geometric character.

It is the principal intention of the classification, as explained, to distinguish formsaccording to the basic lighting and room-size categories and to describe complexassemblies in terms of these simpler components. This rule has, however, been broken,because of the contingencies of coding, in three frequently occurring cases. Specialc̀omposite' codes are provided for a cellular sidelit strip around artificially lit or toplitopen plan space (CDO); a cellular daylit strip around a hall or halls (CDH); and, asalready mentioned, a cellular sidelit space within an open plan shed (CDS). Where

Table 1. Principal form types.

CS4 Daylit (sidelit) cellular strip, 1 to 4 storeysCS5 Daylit (sidelit) cellular strip, 5 storeys or moreOD4 Daylit (sidelit) open-plan strip, 1 to 4 storeysOD5 Daylit (sidelit) open-plan strip, 5 storeys or moreCT1 Toplit cellular, single-storeyHD Daylit hall, either sidelit or toplit (or both)HA Artificially lit hallOS Open-plan space in a single shedOC1 Open-plan continuous single-storey spaceOG Open-plan car parking or trucking deckOA Artificially lit open-plan multistorey spaceSR Single-room formSSR String of single-room formsRA Railway arch

Composite form types with special codesCDO Daylit (sidelit) cellular strip around some or all edges of artificially lit or toplit

open-plan spaceCDH Daylit (sidelit) cellular strip around some or all edges of artificially lit or toplit hallCDS Open-plan shed with daylit cellular strip or strips inside, along one or more edges


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CS4

CS5

OD4

OD5

CT1

HD (sidelit)

OS

OC1

OG

OA

HD (toplit)

SR

SSR

RA

CDO

CDS

Figure 12. Diagrams of principal forms (see table 1 for key). Arrows show the directions ofdaylighting. (No diagram is shown for HA, `artificially lit hall', which is equivalent to HD inform.)


possible, use of these codes has been avoided. They have only been necessary wherebuildings had already been broken down geometrically into floor polygons in theSmallworld GIS in ways which were not compatible with the simple built form cate-gories.

Table 2 lists all the parasite forms in the classification, and figure 13 gives illus-trations. Note that atria and covered streets or arcades (as found typically in shoppingcentres) have been treated as parasites rather than as open-plan space because of theirspecial structural and glazing characteristics and the fact that they would never exist asindependent entities. The decision was taken initially to treat basements (other thanbasement car parks) and occupied pitched roofs or attics as parasites, rather thaninclude them with the principal built forms. In subsequent analysis, however, thisdecision has been reversed (see Steadman et al, 2000b).

A few additional codes are provided for other subsidiary forms, comparable withparasites, but which are not actually attached to their `hosts'. Some of these arespecialised structures or large machines, for example training towers for firefightingpractice, car washes, and bus washes. Outdoor swimming pools have been coded,despite their not being `buildings', because of their use of energy.

PRCL

CB

AT

PC

CT

AGOR

BA

EX

AI PO

AR

BL

AC

Figure 13. Diagrams of parasite forms (see table 2 for key).

Table 2. Parasite form types.

AC Attached open-sided canopyAG Attached glasshouse or conservatoryAI Monopitch aisleAR Covered street or arcadeAT AtriumBA BasementBL Large balconyCB Circulation bridgeCL Covered enclosed ground-level circulation linkCT Attached circulation towerEX Small single-storey extensionOR Occupied pitched roof or atticPC Porte cocherePR Roof-level plant room


The classification appliedAll floor space at the 3350 addresses in the four townsöamounting to some 4 million m2

in totalöhas been coded according to this classification. There are nevertheless someindeterminate boundaries between the categories, which made this process slightly morearbitrary than it might otherwise have been. Readers will have noticed that, althoughdistinctions between types of space are based in principle on room size, no actual limitson area or plan dimensions have been specified. The precise thresholds, for examplebetween a large cellular room and an extent of open-plan space, or a large cellular roomand a hall, are left undefined. `Small single-storey extensions' are treated as parasiteforms, without quantifying what is meant by `small'. Another kind of uncertainty incoding occurs where a continuous extent of open-plan space is partly daylit and partlyartificially lit but the precise boundary is difficult to define (and would be, even withaccess to actual measurements of light levels).

These problems aside, it proved straightforward in practice to assign the major partof the floor space in the four towns to the categories in tables 1 and 2. But the codingwas hampered in other cases by the fact that neither internal plans nor detailed dataon artificial lighting were available. Although the classification is focused on externalenvelopes, the forms of these envelopes are nonetheless determined in part by thecharacter of the internal layout. The value of any analytical results would no doubthave been even greater, had the built form categories been that much more sharply andquantitatively defined. All this said, the data set of the four towns provides a unique`laboratory' for investigating built forms and their relationships, both with activitiesand with building construction, at a statistical level. (It should be emphasised that allfloor areas and wall lengths are measured with great precision and that all data onstorey heights and roof slopes are also reasonably reliable.)

Table 3 gives the total gross external floor area of floor space devoted to each typeof principal form in the four towns. The picture is dominated by two types, the sidelitcellular up to four storeys (CS4) and the composite sidelit cellular around artificially litopen plan (CDO). The former accounts for more than half of all floor space, and thelatter for nearly a quarter. The majority of the corresponding activities are offices,shops, and hotels with shallow and deep plans respectively. The `shed' types OS andCDS, and the single-storey open plan OC1, between them account for some 15% offloor space, the majority used for warehouses, workshops, and factories, as would beexpected. These same uses, together with shops and offices, account for much of theOA open-plan artificially lit multistorey space (5.5% of the total). Several principalform types are negligible in terms of floor area, notably CT1, CDH, and SSR.

In Steadman (1994) some statistics were given to illustrate the relationship of builtforms to activities in these data. For every built form type, the floor area was com-puted for each of the whole range of activities, classified according to `primary descrip-tions' used by the Valuation Office of the Inland Revenue (Bruhns, 2000). Theseanalyses confirmed the points made at the beginning of this paper about the flexibility ofmany types of built form. Activities such as shop and office are found in almost all ofthe principal form types. Conversely, there are certain types of form, notably sidelitcellular space up to four storeys (CS4), associated with almost every activity other thantelephone exchanges and multistorey car parks. At the same time, there are formswhich tend to be more restricted in the range of activities accommodated: thus daylithalls (HD) are concentrated mostly in schools, sports centres, lawcourts, churches, andvillage and community halls, as would be expected. The least flexible form is the carparking and trucking deck (OG), which is of course defined in activity terms: but eventhis is associated with shops and offices, as well as multistorey car parks. In Steadmanet al (2000b) these results are translated into `built form recipes', expressing the typical


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built form composition of premises in a range of size bands devoted to different groupsof activities.

Some statistics are also illustrated in Steadman et al (2000b) for the relationshipsbetween built forms and the constructional characteristics of buildings in the fourtowns. These include the occurrence of structural system types (framed or load-bearing)in built forms of different types and sizes; the relationship of exposed wall areas andglazing areas to floor areas, in different types of built form, especially the sidelit types;and the association of different geometric forms of roof with built forms of differenttypes. Such relationships are being used to make inferences about construction, materi-als, and the surface areas of buildings in the national stock. Beyond this immediateapplication, the work takes the first steps towards a new kind of quantitative study ofbuilding morphology, devoted not to theoretical forms but to a mass of empirical dataon existing buildings. Such a programme could not be contemplated without a resourcesuch as the four towns database, in which the geometry and construction of very largenumbers of actual buildings are fully and consistently represented along with thepatterns of activity which they accommodate.

ReferencesBaker N, Hoch D, Steemers, 1994 The LTMethod Version 1.2 Commission of the European

Communities Directorate-General XI, Cambridge Architectural Research and Martin Centrefor Architectural and Urban Studies, University of Cambridge, Cambridge

Bemis A F, 1936 The Evolving House (MIT Press, Cambridge, MA)Brown F E, Steadman J P, 1991a, `̀ The morphology of British housing: an empirical basis for policy

and research. Part 1: functional and dimensional characteristics'' Environment and Planning B:Planning and Design 18 277 ^ 299

Table 3. Total gross floor areas (square metres) in principal form types, in the buildings surveyedin four English towns.

Type Floor area, m2 percentage

CS4 1 343 247 33.9CS5 207 516 5.2OD4 36 615 0.9OD5 79 632 2.0CDO 771 402 19.5CT1 4 204 0.1HD 33 967 0.9HA 26 555 0.7CDH 9114 0.2OS 224 676 5.7CDS 106 454 2.7OC1 245 359 6.2OG 173 558 4.4OA 216 322 5.5SR 23 456 0.6SSR 4 087 0.1RA 20 378 0.5

Parasitic formsBA 245 809 6.2CT 32 902 0.8EX 31 992 0.8OR 37 896 1.0All others 84 032 2.1

Total 3 959 173


Brown F E, Steadman J P, 1991b, `̀ The morphology of British housing: an empirical basis for policyand research. Part 2: topological characteristics'' Environment and Planning B: Planning andDesign 18 385 ^ 415

Brown F E, Rickaby P A, Bruhns H R, Steadman J P, 2000, `̀ Surveys of nondomestic buildingsin four English towns'' Environment and Planning B: Planning and Design 27 11 ^ 24

Bruhns H R, 2000, `̀ Property taxation data for nondomestic buildings in England and Wales:''Environment and Planning B: Planning and Design 27 33 ^ 49

Bruhns H R, Rickaby P A, Steadman J P, Moss S, Herring H, 2000, `̀ Types, numbers and floorareas of nondomestic premises in England and Wales, classified by activity'' Environmentand Planning B: Planning and Design 27 forthcoming

Clay F, 1902 Modern School Buildings (Batsford, London)Department of Education and Science and Welsh Office, 1977 A Study of School Building (HMSO,

London)Ham R (Ed.), 1972 Theatre Planning (Architectural Press, London)Holtier S, Steadman J P, Smith M G, 2000, `̀ Three-dimensional representation of urban built

form in a GIS'' Environment and Planning B: Planning and Design 27 51 ^ 72Joedicke J, 1962 Office Buildings (Crosby Lockwood, London)Klose D, 1965 Multi-storey Car Parks and Garages (Architectural Press, London)Kru« ger M J T, 1977 An Approach to Built Form Connectivity at an Urban Scale PhD thesis, School of

Architecture, University of Cambridge, CambridgeMarch L J, 1972, `̀ Elementary models of built forms'', in Urban Space and Structures

Eds L Martin, L March (Cambridge University Press, Cambridge) pp 55 ^ 96Steadman J P, 1994, `̀ Built forms and building types: some speculations'' Environment and

Planning B: Planning and Design 21 s7 ^ s30Steadman J P, 1998, `̀ Sketch for an archetypal building'' Environment and PlanningB: Planning

and Design 25 (Anniversary Issue) 92 ^ 105Steadman J P, Bruhns H R, Rickaby PA, 2000a, `̀An introduction to the national non-domestic

building stock database'' Environment and Planning B: Planning and Design 27 3 ^ 10Steadman J P, BruhnsHR,Gakovic B, 2000 b,``Inferences about built form, construction and fabric

in the nondomestic building stockof England andWales''EnvironmentandPlanningB:Planningand Design 27 forthcoming






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A classification of built forms

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