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Systematic procedure for setting building flexibility targets
Arto Saari
Helsinki University of Technology, Construction Economics and Management, Box
2100, 02015 HUT, Finland, E-mail: [email protected]
Abstract: The aim of the research was to determine: Which factors can be used to affect the flexibility
of a building? How should flexibility be taken into account in decision-making concerning construction
projects? In the presented method of setting flexibility goals, the modifiable flexible spaces are defined
first. It is essential that project-specific flexibility goals be set for modifiable spaces, for instance, with
respect to divisibility into separate rental units and flexibility of the space program. The base building is
dimensioned on the basis of the definition of modifiable spaces. It includes dimensioning of the
permanent frame section and permanent building services. The infill of the building’s modifiable
spaces is determined at later stages of the building project as the occupancies of the spaces are
“fixed”. The infill of various sections of the building may be attached one at a time as the project
advances. In order to remain within the budget of the building project, it is important that financing is
based on the most expensive combination within the limits of flexibility. The presented method suits
both new construction and refurbishment.
Keywords: Building, Programming, Flexibility, New construction, Refurbishment
Introduction
The Dutch pioneers of open building, John Habraken and Age van Randen, have
since the 1960s developed the idea of dividing a building into a permanent support
and a modifiable infill section. They thought of breaking up residential building
construction into two independent processes. The task of the support, which is the
permanent section of a building, is to provide space protected from the elements. It
can be divided into individual unitsof varying sizes in the ideal caseso that
fluctuations in demand can be met now and in the future. The permanent support
incorporates all common systems such as entrances, stair wells, lifts as well as the
fixed parts of electrical, water, gas, etc. systems up to the ”front door” of each space
unit. The modifiable infill serves individual spaces by providing building services,
partition walls, doors, equipment, kitchen and sanitary fixtures, internal surfaces, etc.
The service life of the permanent support is long compared to the modifiable infill
(van Randen 1996).
The basic principle of open building is to find ways of dividing and combining
subsystems so that their interdependencies are minimized. (see Fig. 1). Application
of this principle allows efficient buildings as well as redesigning or renewing a
subsystem to correspond to different features without redesigning and renewing the
entire system (Decker & Kendall 1996).
Proceedings of the CIB W070 2002 Global Symposium
Copyright © 2002 by CIB and CABER
116
Figure1. Decision-making levels in open building (Source: Decker&Kendall 1996).
Francis Duffy and John Worthington have also emphasized that the different service
lives of various parts of an office building must be considered. Already in 1972 they
introduced the ”shell-scenery-set” scheme which depicts the differentiation of
building sections that perform differently time-wise. The most durable parts of a
building such as columns, beams, foundations, roofs and bearing walls are structural.
Consequently, they are difficult to replace or redesign and rebuild. These structural
components determine the location of other building parts. Thus, they must be
designed so as to enable different mechanical systems and space arrangements in
the future. The shortest-lived parts of a building, again, must be such that office
workers themselves can control and alter them which promotes individuality and
creativity.
Steward Brand developed the stratification idea of the building further. He divides the
building into the following parts: site, structure, skin, services, space plan, and stuff.
Figure 2. Building stratification by Steward Brand. Source: Duffy 1997.
Systematic procedure for setting building flexibility targets
Saari, A.
117
In the United States and Canada, the building has been divided into three parts in
office and commercial construction for at least two decades (Kendall 1996): the base
building, interior construction and furnishing, fixtures and equipment.
Base buildings are designed and constructed without a space plan based on various
tenants or considering furnishing, fixtures and equipment. As soon as a unit has been
sold or rented, it is adapted to the user’s needs. Later on, individual units are adapted
to the needs of new users causing as little disturbance to other tenants as possible.
In the above-mentioned countries the entire process of building and renting office
and commercial space has been adapted to the described plan.
This paper presents a procedure which allows setting targets for the flexibility of
buildings at the project programming phase.
Flexibility of building
User’s viewpoint
The important factors from the viewpoint of users affecting flexibility are:
• Spaciousness (e. g. space per capita)
• space plan of rental unit and ease of its modification
• air change rates, cooling capacity, lighting capacity, etc.
• available common spaces and services.
The users of a rental unit are interested, especially, in the operative use flexibility of
the unit and its facilities, which indicates how well the unit adapts to the changing
needs of the user. Needs may change at intervals of a few years or, in extreme
cases, of just minutes. The use flexibility of a space or unit can be affected by its
universal applicability as well as its modifiability. Use flexibility is especially important
to the users of a space.
Owner’s viewpoint
The following features of buildings are the least adaptable to change:
• available room height
• horizontal openness of bearing frame
• load-bearing capacity of building frame
• layout and capacity of vertical traffic routes (stair wells, lift shafts, mechanical
shafts and ducts).
Of course, the mentioned features of an existing building can be altered, but the
related costs are extremely high. If we design a more spacious building with regard to
the mentioned features, the building will be more adaptable to presently unknown
occupancies.
Strategic flexibility describes how well a building adapts to possible changes after
years. Such changes are required, for instance, by changes in the operations of
space users, new users of spaces, a general change in the nature of work, and
structural change of society.
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Saari, A.
118
Strategic flexibility is an important feature for the building owner who must consider,
already at the investment phase, whether to invest in a more expensive and more
flexible alternative. After all, the option purchased at a high price may turn out to be
an unprofitable investment (no change occurs, or the change is completely different
than expected). It is also possible that if the cheaper and less flexible solution was
chosen, the costs (NPV) from the change are essentially larger than the price of the
option.
Differences between new construction and refurbishment
In refurbishment, the starting point is an existing building of a certain shape, number
of floors, frame depth, floor height, stair well system, frame system, and space plan.
Thus, the building can be highly unadaptable to major changes at present and over
its coming life span. It is easier to increase operative use flexibility than strategic
flexibility, which the owner values more, when refurbishing existing buildings.
In new construction projects the same constraints do not apply. The strategicflexibility features are more freely selectable than in refurbishment.
Consideration of the change cycle
Demands on buildings change over time. The demands can be met in two ways,
either by:
1. altering the building physically as requirements change, or
2. by incorporating in the building versatile or universal features.
In the first instance, the costs of the change are incurred at the time the change takes
place. In the second instance, hardly any costs are incurred as the need
changesthe costs were incurred already at the construction phase in preparation
for possible future changes.
Building
flexibility
low
Building
flexibility
high
Use type 1
User 1
Use type 2
Use type 3
Use type 4
User 2
Use type 5
Use type 6
Use type 1
User 1
Use type 2
Use type 3
Use type 4
User 2
Use type 5
Use type 6
Time
= disturbance to users/alteration costs
Figure 3. Investments to building flexibility decrease disturbance and alteration costs.
The cycle of change determines largely which method is more advantageous. If the
cycle is long, tens of years, it is generally more economical to choose the cheaper,
less adaptable option (e.g. a fixed board partition). Should the cycle be essentially
shorter (a few years), the more flexible option is generally better justified (a
Systematic procedure for setting building flexibility targets
Saari, A.
119
demountable and reinstallable system wall). In the case of an extremely short cycle
of a month or maybe a few hours, an essentially more flexible solution is called for
(e.g. a wall that slides on tracks).
Setting of flexibility targets for a building
The programming of a building project is done at an early phase before building
designs are drawn and work commences. In programming, the quantitative,
qualitative, financial, and time-wise targets of the building project are set.
In order to program flexibility into the project, one must establish what kind of spatial
flexibility is required of the building. Flexibility may be needed due to the fact that the
users of the building are not known (construction-phase flexibility) or to allow for
changes in building occupancy over its life cycle (life time flexibility).
Users of buildings are primarily interested in the spaces and their features. Thus, we
should determine what kinds of spatial features a building must be able to offer
immediately on its completion as well as over its life cycle. Therefore, programming
starts with setting of spatial flexibility requirements.
The highly unadaptable parts of a building such as the bearing frame and technical
routings limit changes. Thus, it is important to set flexibility targets already at the
programming phase for the base building composed of the permanent parts.
Required spatial flexibility
Flexibility of base building
Figure 4. Programming starts with setting of spatial flexibility requirements. It is
important to set flexibility targets already at the programming phase for the base
building composed of the permanent parts.
Required spatial flexibility
In order to be able to define and dimension the base building, the limits of the
features of the modifiable spaces must be defined.
The modifiable spaces consists of those building spaces whose occupancy or use
may change. Changes may take place during the building process or the use of the
building. The infill of the modifiable spaces of the building is ”fixed” at a later stage of
the building project when the occupancies of spaces are finalized.
Systematic procedure for setting building flexibility targets
Saari, A.
120
The following features of modifiable spaces are established:
Divisibility into units:
Number, size, limits, and independence of units.
Example: One should be prepared for the fact that the building may be divided into rental units of
about 200 m2 or its multiples. Walls between units cannot be bearing. The requirements apply to
flexibility during construction and building use. The units must be independent. Each one must have its
own entrance with a lockable door.
Space programme flexibility:
Space designations, no. of spaces, and their features
Example:
office rooms
open-plan office space
conference rooms
close-by storage space
toilet facilities
total (max)
300-1,600 m2 /ea. 10-20 m2 / 20-150 people
0-1,000m2
/
0-125 people
100-200 m2
200-400 m2
0-40 m2
2,600 m2
Indoor air quality requirement class is S2. If the toilet facilities are not implemented, water and drain
pipes are nevertheless laid up to the space in question. Otherwise, space requirements will become
more specified as the users of spaces become known.
Permanent spaces:
Some spaces of the building need not be modifiable or are so specialized that it is
not worth making them flexible.
Example:
car park
lobby
auditorium
toilets
service space
stair wells
corridors
mechanical room
other mechanical space
civil defence shelter
Total
420
100
100
30
60
130
260
200
40
60
1,400
m2
m2
Flexibility of base building
The base building incorporates all the physical building parts that need not be
changed or altered even if anticipated changes take place during construction and
use.
The definition and dimensioning of the base building involves:
Available room height:
Example: Clear height of modifiable spaces must be at least 3.5 m. Clear height is measured from the
floor surface to the underside of a bearing structure in the ceiling of the space.
Horizontal openness of bearing frame:
Example: The target gross area of the building is 4,500 m2. It must be possible to expand the building
in at least one direction (+50 %). The span of the building frame must be at least 9 m. Modifiable
Systematic procedure for setting building flexibility targets
Saari, A.
121
spaces must not incorporate bearing partitions. Facade fenestration must accommodate different
combinations of modifiable spaces.
Load-bearing capacity of building frame:
Example: Building frame must withstand a floor load of at least 5 kN/m2.
Flexibility of technical routings:
Example: The vertical routings of the building’s technical systems must be dimensioned according to
maximum capacity + 50 %, and the horizontal routings are to be dimensioned according to maximum
capacity +25 %..
Flexibility of technical systems:
Example: The building’s max. design value for ventilation is 10.5 m3/s and the min. value 9.5.m3/s. The
vertical and horizontal main air distribution ducts and ventilation equipment are to be dimensioned
according to the max. values.
Budgeting the building project
In order to be able to prepare a sound financing plan for the project, a ceiling for the
construction costs must be set. The ceiling is determined by including the most
expensive modifiable infill in the budget. The budget is broken down into support and
infill parts. The infill budget is revised as more is learned about the users of the
building.
Example: The ceiling price for construction costs is €6.5 million euros. Project financing is based on
the ceiling price. The base building’s share of the ceiling price is €3.6 million which also constitutes the
budget of the base building. The share of infill is €2.5-2.9 million. The infill budget is revised as the occupancy of the spaces becomes known. The ceiling price for the infill is €2.9 million.
Summary
The target setting procedure for flexibility of buildings defines initially the modifiable
spaces. The essential feature is that flexibility targets for spaces are project-specific,
for instance, with respect to divisibility into units and flexibility of the space
programme. The base building is defined on the basis of the modifiable spaces. The
infill of the modifiable spaces of the building is determined during later stages of the
building project as the occupancies of spaces are finalized. The infills of various
building parts can become attached piecemeal as the project proceeds. To ensure
that the project stays within budget, the financing should be based on the most
expensive combination within the limits of flexibility. The procedure is applicable to
both new construction and refurbishment.
The presented method of programming building flexibility needs to be tested in pilot
projects.
Systematic procedure for setting building flexibility targets
Saari, A.
122
References
Decker K., Kendall S. 1996. Open building, CIB Work Commission on Open Building, 11 p.
Duffy F. 1997. The new office, London: Conran Octobus Ltd, 256 p.
Kendall S. 1996. Developments toward open building in the United States, 3 p.
Saari A. 2001. Tavoitteiden asettaminen rakennuksen muunto- ja käyttöjoustavuudelle (Systematic
target setting procedure for the flexibility of buildings), Helsinki University of Technology,
Laboratory of Construction Economics and Management, Papers 36, Espoo, 31 p. (Only in Finnish)
Systematic procedure for setting building flexibility targets
Saari, A.