cost analysis by Davis Langdon

106 TALL BUILDINGS: A STRATEGIC DESIGN GUIDE

107KEY TECHNICAL COMPONENTS

Optimal design solutions can identify‘appropriate cost’. When factored into abuilding’s performance, this can have ameasurable influence on theproductivity of the spaces enclosed. Itmay or may not support the initial costof a building (as space from which totransact business) over its operationallife cycle. The creation of a landmark is arelated issue.

Procuring tall buildingsThe size, complexity and duration of tallbuilding projects means that there are alimited number of ways to design andconstruct them, in terms of bothstrategy and the range of designers,contractors and specialists with theskills, experience and resources toundertake the work. This sectionconsiders key issues in developing asuccessful procurement strategy for tallbuildings.

STEVE WATTS DAVIS LANGDON

cost:�The cost and scarcity of developable land, thepermitted footprint, building bulk, quality ofspecification, and the time required for design,construction, occupation and use are all genericcost drivers of buildings. The cost of anyparticular mix of these influences the economicsof a building – whether short, tall, large or small.

� Tall buildings in the City of London.The historic street pattern of the City of Londoncreates small, often complex footprints. Theproximity of listed buildings and conservation areasinfluences the modelling and articulation of tallbuildings. Both factors serve to produce structuresof relatively high cost.© Hayes Davidson


Speed and efficiencyOne of the main opportunities of tallbuilding design and construction is theability to exploit the benefits ofstandardisation and repetition acrossmajor cost elements, such as thefaçades. The scale of tall buildingsmakes this true even when a building isbespoke. Achieving and maintainingspeed is critical to successful projectdelivery. Procurement strategies thatallow the overlapping of design,procurement and construction areessential to achieve acceptable projectdurations.

To optimise the programme andeliminate potential sources of delay anddisruption, it is vital to invest in strategicconstruction planning and buildabilityreviews at an early stage. Key elementsin programming tall building projectsinclude:

� Management and co-ordination oftrade activities on site, to maintainthe cycle of floor construction

� Management of extended design andprocurement programmes, to permit themaximum degree of standardisationand minimise floor constructioncycles

� Optimising the use of standardised and pre-fabricatedcomponents and other measures topromote ‘buildability’.

Specialist contractorsThe procurement of specialistcontractors is strongly influenced by thesize of packages involved. It can bebeneficial to bundle related trades into a

single package with unitedmanagement. Examples of this are corearea fit-out works and servicesinstallations. The early appointment ofspecialist contractors is essential toprovide for their early design input andco-ordination. For example, a concretetrade contractor may influence thechoice of core construction method,which could result in changes to itsdesign.

LogisticsProvision of sufficient cranage andhoisting is critical to maintainprogramme. Co-ordination of deliveries,cranage slots and constructionprogrammes is necessary to ensure thatspeed is maintained. Efficient transportof people and materials is crucial toachieve productive utilisation of labour.On tall structures, the added time takento travel to and from higher levelworkfaces calls for attention to verticaltransport during the construction periodand provision for worker welfare aboveground level. The location of toilets andcanteens at regular intervals up thebuilding will minimise downtime andprevent delays through unnecessaryjourneys in hoists.

Health and safetyHealth and safety is a major issue whenworking at height. The attention paid tothese requirements during tall buildingconstruction in the UK means that therisk is generally well managed. One ofthe benefits of working on largebuildings is that trades do not need towork on top of one another, with the riskof minor incidents accordingly reduced.

� Canary Wharf, including proposals by RichardRogers Partnership (shown to right of the cluster),reflects the relative lack of constraints on eitherfootprint or building form, resulting in large regularblocks which are relatively cost-effective toconstruct.Canary Wharf Group plc/© Miller Hare

109COST


Cost overviewHeight is not the sole criterion in theconsideration of the relative cost of tallbuildings. The size of the floor plate, theoverall proportion of the building, itslocation and degree of architecturalexpression will all have a fundamentalimpact on cost. This section looks at anumber of indicative construction costmodels based on building designs thatvary according to these criteria.

Site issuesSite constraints, such as adjoining structures and existing services obviously affect cost.

Height, shape and geometryThe most sensitive cost drivers are the specification and the extent of the frame and envelope. These are determined particularly by planning issues, the floor plate design and the environmental strategy, which affect the wall to floor ratio, structural complexity, core design and envelope performance criteria.

Services strategyThe environmental solution needs to be developed alongside the thermal performance of the façade. Cost drivers include: aesthetic intent, requirements for flexibility, building usage / operational issues, availablespace for plant and whole life costs.

Lift strategyPopulation distribution, building functions, performance targets and factors that affect the core design, e.g. orientation of building entrances, structural considerations and escape strategies, all combine to influence the design and economics of the lifts and escalator installations.

Building usesThe costs of single occupancy versus multi-let buildings and the design complexities associated with accommodating multiple uses within a single building are relevant.

Building ownershipDrivers include the quality of design and materials, investment to reduce whole life costs, applications for sustainability and requirements for flexibility and redundancy.

Regulations and preferred practiceDesign responses to Part L of the Building Regulations, together with enhanced performance for sustainability have cost implications.

Life safetyEnhancements for safety and security, including requirements for bomb-blast measures to cladding, structural collapse resistance, fire protection enhancements, evacuation improvements and provision of diverse support systems are other drivers.

Tall office buildings: for shell and core constructioncosts.

Principal cost drivers. � © Davis Langdon LLP/KPF

111COST

Indicative costsThe following four models considerindicative costs based on key designvariables relating to the design andconstruction of tall buildings.

Floor to Floor = 4m

15

1944m²GEA

1944m²GEA

1944m²GEA

1944m²GEA

30

45

60

14,580m²GEA

4374m²GEA

1944m²GEA

45

206

Floor to floor = 4m

Urban peripheryLarge floor plate, regular planLimited external articulation

1944m2

GEA 2835m2

GEA

45 45

City coreSmall floor plate, irregular planArticulated, high performance envelope

Floor to floor = 4m

Floor to floor = 4m

m

1215m²GEA

X 45 = 54,675m² X 45 = 72,900m² X 45 = 87,480m² X 45 = 127,575m²

1620m²GEA

1944m²GEA

2835m²GEA

4545 45 45

Cost Model One: Building height

Constant plan size, varying heights.� © Davis Langdon LLP/KPF

Cost Model Two: Plan size

Constant height, varying size floor plate.� © Davis Langdon LLP/KPF

Cost Model Three: Proportion

Enclosing identical amounts of gross floor space inbuildings of varying height and floor plate.

� © Davis Langdon LLP/KPF

Cost Model Four: Articulation

Comparing a more architecturally expressive building,as could be required in the City of London, with the'straight-up-and-down' form used for the baseanalysis that is more feasible for a peripheral site.



Cost Model One: height

Irrespective of floor plate, shape, formand other factors, tall buildings costmore to construct per unit of floor areathan low rise buildings, despite theopportunities they offer in terms ofrepetition and sequencing. This relatesto:

� their increased wind loadings andheavier frames

� their vertical transportationrequirements, particularly liftcapacities, speed, zoning, etc.

� the larger capacities of plant anddistribution systems together withthe increased pressures/hydraulicbreaks that are required to deal withthe increased vertical distances

� the effects of their scale andcomplexity on the movement ofmaterials and labour

� the risks associated with theiruniqueness and the fact that theserisks are exacerbated by scale andthe need to access a limited pool ofskills and expertise

� the potential interest in includingelective security and safetyenhancements in response topossible risks (although acceptableresponses can be provided atrelatively little additional cost).

Cost Model One provides a notionalindexing analysis for 15, 30, 45 and 60storey buildings. It shows that theprincipal cost drivers that differentiatethe taller from the shorter buildings(with constant floorplates) are:structure, façades and verticaltransportation. In contrast to a typicalcity centre situation in which thebuilding is likely to be more articulated(see Cost Model Four and associateddiscussion), this theoretical model isconstructed with constant floor plates,thereby ensuring identical wall to floorratios and hence relatively littledifference in the cost of external walls.Arguably the most important finding thatCost Model One shows is the trend forfloor area efficiencies to reduce as theconstant floor plate building increases inheight. The actual efficiency achievedwill depend on various factors including:services strategy, structural design, liftarrangements and building use.

Floor to Floor = 4m

15

1944m²GEA

1944m²GEA

1944m²GEA

1944m²GEA

30

45

60

� Cost Model One: the impact of changing buildingheight on building efficiency and cost.© Davis Langdon LLP/KPF

Floor to floor = 4m

113COST

15

1944m²GEA

1944m²GEA

1944m²GEA

1944m²GEA

30 45 60

75%

70%

68%

65%64%

50%

Efficiency Overall net / gross

15

1944m²GEA

1944m²GEA

1944m²GEA

1944m²GEA

30 45 60

100%

150%

100%

115%

125%130%

50%

Cost / m² Shell and core costs

� Efficiency: the ratio of net togross space – the building’sefficiency – will decline withincreased height. This reflectsthe larger core area required toserve a greater number offloors.© Davis Langdon LLP/KPF

� Shell and core costs: shell andcore cost per m2 rise withbuildings of increased height.© Davis Langdon LLP/KPF


Main cost drivers of tallbuildingsThe relative effect of the four principalcost drivers will differ in each costmodel.

StructureThe building’s height, volumetric shape,plan form, core location and columnspacings all combine to determine themost efficient and cost-effectivestructural solution. Irrespective of thestructural system, the mass and cost ofthe structural frame will increase withheight. Counteracting wind loads, whichincrease disproportionately with height,adds significantly to loads and costs.

Both material efficiency and buildabilityhave a greater cost impact with height.These need to be considered hand-in-hand. An important factor will be thesize of the structural members. This hasa bearing on buildability and speed, anda possible impact on lettable floor areas.The selection of the structural systemwill therefore be determined by cost,building movement, space take-up,aesthetics, buildability and speed ofconstruction. As with the other principalelements, it is important to focus on asingle solution at an early stage of thedesign process.

FaçadesTall buildings are typically designed witha totally sealed external envelope. Thefaçade’s contribution to environmentalcontrol is crucial. With increasingattention to carbon emissions, the designof façades and services installationsneeds to be developed in unison.

More often than not, tall buildings will beall-glazed and the façades will comprisedouble walls (triple-glazed). It will bemore efficient and sustainable to use thefaçade to control heat gain rather thanrely on cooling installations to mitigatethe performance of the envelope. Anumber of factors will affect how this isachieved. These are principally cost,performance, operational robustness,space take-up, aesthetics and ease ofconstruction.

Beyond the detailed performance of theenvelope, the design should seek to take

maximum advantage of economies ofscale, both in factory production and onsite. With large areas of external walling(and high wall to floor ratios), efficiencyof both production and installation arecritical. This can be achieved byrationalising cladding types and fixingdetails through maximum repetition(without compromising aesthetics),ensuring that panels can be fixed fromthe floors rather than having to rely oncranes, and by unitising as much of thesystem as possible.

As well as the environmental strategy,the façade’s interaction with thestructural frame is important. Tolerancesand movements should be addressed at

the earliest opportunity, with slab edgelive loads restricted to say 12-15mm toensure a competitive curtain wallsolution.

Should the design succeed in theserespects, there is every reason to expectthe economies of scale to offset anypotential additional costs associated withfactors such as increased wind loadingsand logistics. However, the cost of theexternal walls is still likely to show asignificant increase relative to those forlow buildings, when expressed per unit offloor area, because of the higher wall tofloor ratios that tend to be inherent to tallbuildings. Slender tall buildings will beparticularly affected in this respect.

200

180

160

140

120

100

80

60

40

20

0

Substr

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re

Super

struc

ture

Extern

al wall

s and

doo

rs

Inte

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walls,

finish

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nd fit

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MEP se

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sLif

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Main

cont

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relim

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on-

costs

Tota

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ll and

core

cost

� Elemental costs for a 30 storey building (baseline costs for a 15 storey building).© Davis Langdon LLP/KPF

Construction costs per unit of area rise with increasing height. Thefollowing diagrams illustrate how costs for building elements change withheight. Rates are expressed as a percentage of the construction cost for atypical 15 storey building.

115COST

200

180

160

140

120

100

80

60

40

20

0

Substr

uctu

re

Super

struc

ture

Extern

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s and

doo

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Inte

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walls,

finish

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MEP se

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sLif

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Main

cont

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relim

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s and

on-

costs

Tota

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core

cost

200

180

160

140

120

100

80

60

40

20

0

Substr

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re

Super

struc

ture

Extern

al wall

s and

doo

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Inte

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walls,

finish

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MEP se

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Main

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cost

� Elemental costs for a 45 storeybuilding (baseline costs for a 15 storeybuilding).© Davis Langdon LLP/KPF

� Elemental costs for a 60storey building (baseline costs for a 15 storeybuilding).© Davis Langdon LLP/KPF


Vertical transportationCore design is the crucial starting pointfor developing the internal operation of atall building. It determines both thebuilding’s development efficiency and itsoperational effectiveness. Together withstructural considerations, and to a lesserextent services distribution, the designof the lift installation is a fundamentalpart of optimising the core arrangement.

The aim of the lift and escalatorinstallations is to optimise travel times andwaiting intervals with the building’s likelypopulation profile in mind. Achieving thisinvolves a significant level of specialistanalysis, the result often representing abalance between number of lifts, liftspeeds, size of groups, zoning of thebuilding, core size and arrangement.

With an increase in building heightcomes an increase in strategic optionsto achieve these targets economically.

The fundamental options are:� Straightforward zoning of floors, with

transfer levels

� Sky lobbies served by express lifts

� Double-deck lifts

� A combination of the above.The use of sophisticated controls, suchas destination hall call, could beincorporated to improve overallperformance. A cost/benefit analysis ofsuch options will determine theirattractiveness.

Main contractors’preliminaries/on-costsMain contractors’ preliminariesencompass a large complement of staffto manage the design and construction,and an array of accommodation, plantand equipment for use by the client,consultants, construction personnel andother site visitors. Care needs to be

taken to ensure the correct quality andscope of all these items to maximiseefficiencies (and avoid unnecessaryduplication with trade contractors’preliminaries).

Appropriate investment in maincontractors’ preliminaries will mitigatethe pressures on trade contractors’preliminaries, which can often beconsiderably greater for a tall buildingproject, partly due to the logistics ofmoving people and materials to and fromthe workface. The time taken byoperatives travelling to and betweenfloors and welfare facilities such ascanteens and toilets can take up asignificant part of the day.

It is important to minimise theseinefficiencies and manage theconstruction process rigorously, startingwith robust and detailed planning. Anappropriate procurement strategy willalso help to minimise programme andfinancial risks.

� Demoltions: access and cranage.© KPF

� Basement construction: access and cranage.© KPF

Heron Tower, 110 Bishopsgate, KPF:Construction sequence studies.

117COST

To achieve all this will require asignificant level of input from aconstructor, employed to manage thedesign team and the construction andsite processes, and to provide an inputinto planning, procurement and costcontrol. This will include the provision,maintenance and co-ordination ofcommon items of plant, facilities andequipment provided for use by all tradecontractors. This level of input results inhigher costs, associated with staff andplant equipment levels, which will needto be provided for relatively longerperiods. The inherent cost andcomplexity of tall buildings will inevitablyalso result in relatively higher designand construction contingencies, whenindexed against lower buildings (thoughpercentage allowances will notnecessarily be higher).

� Top down construction proposed for basements.© KPF

� Superstructure construction: access and cranage.© KPF


Cost Model Two: plansize

The 45 storey building from the earlieranalysis has been further reviewed toconsider the effect of alternative floorplate sizes – 1,215m,2 1,620m2 and2,835m2 – on area and cost (re-indexedto the tall building).

The effect of varying floor plates on theshell and core cost of a tall buildingshows the principal cost drivers to be:

� Wall-to-floor ratiosThe significantly higher wall-to-floor ratioof a smaller floor plate will result in agreater proportion of costs beingattributed to the envelope. It will alsoaffect the services strategy, which willhave to respond to an increased level ofsolar gain.

� StructureSlender tall buildings require strongerframe solutions for increased stiffness,to counteract the more marked effects ofwind action.

� LiftsA higher lift density will be required toserve the needs of smaller ‘premium’occupiers.

Additionally, where the floor plate issignificantly reduced in slender tallbuildings, opportunities for economies ofscale may be reduced or lost. Net to grossfloor area efficiences are also shown todeteriorate with a decrease in the size ofthe floor plate, relating to relatively largercores on smaller floor plates.

1215m²GEA

X 45 = 54,675m² X 45 = 72,900m² X 45 = 87,480m² X 45 = 127,575m²

1620m²GEA

1944m²GEA

2835m²GEA

4545 45 45

� Cost Model Two: impact of size of the floor plate on the efficiency and cost of a 45 storey tower.© Davis Langdon LLP/KPF

119COST

1215m²GEA

1620m²GEA

1944m²GEA

2835m²GEA

4545 45 45

70%

60%

62%63%

65%

67%

50%

Overall net / grossEfficiency

1215m²GEA

1620m²GEA

1944m²GEA

2835m²GEA

100%

150%

120%

110%

100%

80%

50%

Cost / m² Total shell and core costs

4545 45 45

� Efficiency© Davis Langdon LLP/KPF

� Shell and core costs© Davis Langdon LLP/KPF


Cost Model Three:proportion

Cost Model Three considers the choice ofbuilding form for a given amount ofgross floor area. It shows threepossibilities to provide around 87,000m2

of total gross internal floor area: agroundscraper of 6 storeys (14,580m2

floor plate), a medium-rise building of 20storeys (4,374m2 floor plate), and the 45storey office building which wasanalysed previously. This comparisonresults in the following indicative effectupon the total cost indices.

The combination of decreasing heightand increasing floor plate affords:

� Significantly improved wall-to-floorratios

� More efficiently designed elements(such as the structural frame)

� Faster construction, with a greaterproportion of the building beinghorizontal rather than vertical, andeasier logistics

� More options in the location ofcomponents such as central plant.

14,580m²GEA

4374m²GEA

1944m²GEA

75%73%

70%

65%

50%

Efficiency Overall net / gross

45206

14,580m²GEA

4374m²GEA

1944m²GEA

45

206

Floor to floor = 4m

� Efficiency© Davis Langdon LLP/KPF

� Cost Model Three: impact of proportion onbuilding cost.© Davis Langdon LLP/KPF

121COST

Cost Model Four:articulation This compares a predominantly functional,well detailed but essentially plain buildingform, such as HSBC at Canary Wharf, with amore complex, articulated building typicalof the City of London. The comparisonillustrates key implications of designingand procuring a tall building in a sensitivecity centre location. These include:

� Complex substructures to avoidexisting obstructions and deal withboundary conditions

� A more complicated shape and form,particularly in response to planningconsiderations (e.g. the taperedshape of the proposal for 122Leadenhall Street, predominantly toavoid a viewing corridor to St Paul’sCathedral)

� The higher quality of design andmaterials

� The increased pressures toincorporate an attractive interactionbetween the building and thestreetscape, an architecturalstatement at its pinnacle, and moredemanding planning requirements

� More complex construction issuesresulting in extended constructionprogrammes.

By far the biggest impact on costs willbe the more complex building form, asimplified illustration of which is shownin Cost Model Four (noting that realexamples of this exist, e.g. the Heron,Minerva and London Bridge Towers).

Floor area efficiencies are also likely tobe reduced, possibly through a lessstraightforward core design and moreimpact of structure on the floor plate.

1944m²GEA

2835m²GEA

100%

150%

100%

130%

50%

Cost / m² Total shell and core

4545

Floor to floor = 4m

Urban peripheryLarge floor plate, regular planLimited external articulation

1944m2

GEA 2835m2

GEA

45 45

City coreSmall floor plate, irregular planArticulated, high performance envelope

Floor plate size

� Shell and core costs© Davis Langdon LLP/KPF

� Cost Model Four: articulation© Davis Langdon LLP/KPF


Cost and height

The following principles are involved:� For a constant floor plate, costs per

m2 of floor area increase with height,whilst overall net to gross floor areaefficiencies are reduced.

� The cost/height relationship ischaracterised by step changes, dueto various technical thresholdswhich occur at different heights andfloor plate dimensions. The full costprogression depends on the specificaggregation of the component costsin any given design.

� Larger floor plates are moreeconomic, mainly due to theirsuperior net to gross floor areaefficiencies and improved wall tofloor ratios.

� City schemes constructed in highvalue locations involve a trade-off,with reduced floor area efficienciesand higher cost, because of theirmore articulated façades, morecomplex forms and the otherimplications of a constrained,sensitive location.

� Groundscrapers can provide morenet area for the same overall grossarea provision, at significantly lowerconstruction costs, but involve lessintense – and potentially lesssustainable – use of high value land.

RiskCost-effective enhancements can promotesafety in tall buildings, addressingevacuation, structural collapse and bomb-blast resistance. With buildingmanagement and occupant training,these measures offer economically viableinputs to risk assessment.

A question of value

With many factors at play, the costindices provided here are necessarilyindicative.

Because of the increased unit costs anddecrease in floor area efficiency with tallerbuildings, net space is disproportionatelymore expensive. The viability graph(opposite) illustrates this by plotting thecost in accordance with net internal floorarea.

Irrespective of floor plates, landmarkstatus, form and proportion,development costs per m2 of gross floorarea increase with height. To be viable,the value of tall buildings per m2 mustalso be higher, and market evidencesuggests that it is possible for tallbuildings to provide an acceptable long-term return.

The economics of tall buildings on both amacro and micro scale will varyaccording to their location. The valuesand costs associated with a tall buildingin the Far East are different to one inLondon. London is a ‘young market’ fortall buildings. With the increasedknowledge and experience that comesas more proposals are developed, thecost and efficiency premiums may bereduced. The distinctiveness of qualitytall buildings may also represent avaluable form of diversification withinthe office sector.

123COST

Tall buildings: The pressures on a potential viability curve

Building height

- smaller floor plates- more complex ’urban form’

- larger floor plates- more regular functional form

Shell and coreconstruction costs

per m2


� Irrespective of floor plates, landmark status, form andproportion, development costs per m2 of gross floor areaincrease with height. To be viable, the value of tall buildingsper m2 must also be higher, and market evidence suggeststhat it is possible for tall buildings to provide an acceptablelong-term return.

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cost analysis by Davis Langdon