EDUCATIONAL USE OF AN ELEMENT BASED COST MODEL FOR OFFICE BUILDING IN THE INITIATIVE PHASE
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EDUCATIONAL USE OF AN ELEMENT BASED COST MODEL FOR
OFFICE BUILDING IN THE INITIATIVE PHASE
Peter de Jong
Dept. of Real Estate & Housing, Faculty of Architecture,
Delft University of Technology, Delft, the Netherlands
Email: p.dejong@bk.tudelft.nl
ABSTRACT: Based upon research of hundreds realized office buildings a parametric
approach of quantities of a standardized office design is elaborated in a cost model, enabling
determination of a virtual reference building using a few basic characteristics. Using 'defaults'
most secondary values are given, but can be adjusted to get a better match between the virtual
reference and the design. The qualitative match can be established by selecting building
specifications on element level. This will result in an estimate on element level of the
reference, meeting the design as far as possible, given the restrictions of the type. Finally the
quantities can be adjusted, based upon variation in building layout and qualities can be
superadded, resulting in a reliable detail estimate.
Educational value follows from investigating numerous versions with (slight) variance in
quantity and quality influencing the building costs. Students gain understanding of building
costs and get awareness of cost-quality-ratio.
Keywords - Building costs, Cost model, Education, Office buildings, Ratio cost quality
1. INTRODUCTION
Economy is not about money; it is about scarcity. In many building processes funds as well as
quality are sparse items. The education of architects as well as design managers should not focus
on costs without emphasizing qualities at the same time. Future project managers should learn
not how to minimize cost but how to maximize quality within the limits of a (sometimes elastic)
budget.
Teaching building costs in the Bachelor course of an Architectural Faculty, producing
architects and project managers, is different from teaching building cost consultants of quantity
surveyors. The main goal is cost awareness as a means for design quality. Or, in a more informal
way of speaking, cost awareness without turning creative persons against cost controllers.
Svinsk is a cost model used at the Faculty of Architecture of Delft University of Technology,
created to combine a thorough building cost approach with the focus on quality, presented as an
easy to use tool, even for inexperienced people.
2. RESEARCH
Working in a field in which algorithms and modelling are part of the daily business, the whole
idea in this paper may seem rather obvious, but one should realize that most estimates in building
projects are hardly ever based on intelligent models. The normal estimate consists of quantities,
extracted from the brief, the design drawing or the CAD-model, an estimated cost per unit,
approaching the required quality as far as possible, resulting in a post including the quantity per
unit, the cost per unit and the product, which is the total cost of a certain element (or work item,
labour, material and so on). The total costs of building will be found by summing up the total
amount of different elements. A systematic approach will ensure that all of the elements are
included. The most ‘intelligent’ calculations will deal with the determination of the contractor
costs or the advisory fee.
Given this starting point, working with reference projects is a first step. Searching for a
reference with a similar function will reveal cost per gross floor area. This is the level mostly
used, if any, in architectural reviews. Even this simple approach is precarious, because proper
definition of the used number is rare in these cases. Questions should be: which year, where is it
built, what is the project size, what is the established quality, and what is the relation between
square metres asked for in the brief and square metres realized in the design?
If a reference project shows more detailed information, usability as a reference project is
increasing. If there is enough similarity between the reference and the new project, the cost per
m² gross floor area (gfa) could be reused. If in such a reference project for an inner wall € 53,-
per square metre is used, the same could be used for a new project. The obscurity is laying in the
definition of enough similarity. To what extend are the cost of a m² brickwork in a 2-layer
apartment building comparable to the same m² in a 6-layer apartment building? What is the
influence of the gfa/shape ratio on the amount of façade? How does the project size affect that
square metre?
Still using the more detailed reference project it is possible to investigate more. If quantities
are given as well, one could distinguish several ratios combining floors, roof, façade,
installations etc. Qualities described, can be matched with the new project, even using simple
formulas like 20% more financial space for ICT.
The base of the philosophy behind Svinsk is formed by a group of researchers, joined in a
group named PARAP. They combined professional experience with a common goal, which may
be represented by a single question: how can we bring the information, normally available at the
end of the building process, more to the front.
Fig. 1. Information versus influence
PARAP started back in 1995 as a research group in cooperation with the Dutch Government
Buildings Agency. In one of their research activities, over 200 office buildings were analyzed.
Within this analysis all possible relations where searched and described. An example is the cost
of a parking space as a function of the location, the availability of public transport, the number of
employees and other possible influences. Or less complex the average cost of roof finishinggiven a certain range of quality. These relations are used to complete the first model of the
reference building estimate.
The second step was to use calculated quantities. Within the limits of a single or double
corridor office building type, many design decisions are regulated by standard starting points
(defaults), like the average number of square metres for a office employee, and (national) rules
like the maximum distance between a workplace and a staircase and so on. This resulted in a
second model: quantities as a result of parameterized design and costs based on the historic
formula based approach. The outcome of the model is tested and proven within reasonable
margins with actual building estimates. The model itself has to be maintained: costs are
influenced by time, so at least regular indexing has to be done. This is the state of the art on
which the student application Svinsk is build.
At the same time the research is going on. Costs of building elements are influenced by the
technical solution. Think of the costs of a beam versus the span length or the cost of brickwork
versus the project size. These relations are described in detail, and will be implemented in an
upcoming version of Svinsk, as far as these relations are significant for the level of detail on
which the application is aiming.
The next step in the PARAP research will be unrevealing the installations in a similar
approach along with the contribution of the cost in use. The general idea is of course that
estimates focussing on investment costs do not deliver the required level of information for the
user. He will be better served by life cycle costs.
3. APPLICATION
The purpose of the model is to provide a project estimate. Therefore three main steps are
required: definition of the reference in quantities, definition of the reference in qualities, and
finally adjusting the project estimate in both quantities and qualities.
In order to explain the model the easiest way is to go through these steps. The main vehicle
for the model is Microsoft Excel; due to the customized menus and controlled environment,
using the Visual Basic for Applications, the Excel under layer is not always recognized. It is felt
as an application on its own.
As homage to the original Excel a ‘wizard’ is created, comparable to e.g. the one used for
creating graphs. Our wizard consists of five (sub) steps in order to establish the first main step:
definition of the reference in quantities.
3.1 Definition of the reference in quantities
First the input of the usable area is asked for. The user could choose for calculating the
usable area by giving a number of employees or the required functional area. Like the rest of the
wizard default input values are used, so by giving a number of employees, and accepting all
other defaults, an estimate will be made. Along with selecting any input box a short explanation
is given of the scope of the input. Furthermore a comprehensive on-line help file could be used
all the way.
The usable area will result in a calculated gfa, using default for required area for traffic,
construction and installations, given a certain number of floors. This will result in a ‘design’ of a
floor plan with a regular zoning, along with more detailed information about the space taken bythe construction (façade, inner walls, core and fire segmentation) and traffic area (corridor,
elevators and stair cases). This requires a cyclic approach behind the surface, but with a few
cycles the floor plan could be redrawn. If any default value is adjusted the calculation algorithms
will start again resulting in a new floor plan. See figure 2.
Fig. 2. The input in Svinsk is organised with a ‘wizard’.
In this wizard grey fields are either defaults or calculated values. Only white fields could be
adjusted directly. The building width cannot be changed because this is the sum of the several
zones and the given thickness of the façade and the inner walls. To get another value for the
width, one should change the zoning or the thickness. The building length cannot be adjusted
too, because this is a result of the required gfa and the calculated width.
When the floor plan is acceptable, the next step of the wizard will be the input of regional
parameters. The PARAP-research distinguished region related influences on costs, which are
taken into account by selecting the city. Average foundation costs will also change by the region
(stratum for pole foundation). Just overwrite this if any better number is available. Further
‘regional’ settings are the type of location (inner city or elsewhere) and an indication of public
transport on the site.
3.2 Definition of the reference in qualities
The last step of the wizard is used for a selection of standard ‘quality’ packages for the façade,
the finishing and the installations. These qualities can be adjusted in the reference estimate,
which is created after finishing the wizard.
Every item in the estimate is provided with a set of quality options. If no choice is made, the
default will be used, where the default is based on the most used type, as found by the PARAP-
research. These adjustments are still considered as a part of the reference estimate, since thecalculation of quantities and the calculation of the dynamic element cost are still treated as a
total. Figure 3 is not only showing an example of one of the sets of qualities: behind the pop-up
one could see the items, which are not adjustable by putting in own quantities or costs.
Fig. 3. In the reference qualities are set.
When the reference is completed, by choosing all the required qualities or accepting the
defaults, the ‘virtual’ reference is finished. This reference should be the closest match possible to
the new project, based on the standard, rectangle, single or double corridor office building.
Next there is the option to insert a project estimate. This is presented as a variant, because
several alternatives can be put next to each other. By selecting the variant the internal control of
values is left behind.
3.3 Definition of the project
The first draft of the project estimate is a simple copy of the reference estimate. Adjustments can
be made on the type of elements, a choice of different qualities and the quantities. A small
library of materials is given with the application. The user could insert these materials or create a
new item with a new material.
Fig. 4. On project level the library can be used for detailed materialisation.If Svinsk was not a student version, but a real professional tool, one of the first steps, but at
the same time one of the most time consuming activities would be the maintenance of a complete
and updateable library with element costs. Within the educational setting the limited library will
be enough. For additions one could use the information of commercial databases or using own
references.
While the reference is based on e.g. a single type of façade, in the project estimate different
facades could be combined together. The user should adjust quantities in a way that the total of
different quantities per façade type is still in line with the reference. It becomes slightly more
complicated when for instance an atrium is submitted. Also changing of the building shape may
require second thoughts. The single corridor building will keep the same quantities if it is not a
straight rectangle but L-shaped, or even U-shaped. When the last corner is rounded and the
building is enclosing a courtyard, mayor changes in the façade quantity will take place. Also the
number of required staircases may change.
Fig. 5. Inserted item with adjustment of quantity
The way in which these adjustments are treated is quite simple. If there is any adjustment in
quantity or element cost the adjustment is used instead of the default value.
Finally the application gives some assistance in comparing the variants in tables and graphs.
Effects of adjustments could be made clear in a number of views.
Fig. 6. Overview in tables and graphs.
4. EDUCATION
A rather obvious research question and easy to investigate with Svinsk would be the lowest
building costs for an office building, single or double corridor, with a given usable floor spaceand with variation in the number of floors. Leaving all defaults as is, a usable floor space of 4000
m² will result in the following graph.
Fig. 7. Number of floors versus building costs per m² gfa.
The upper (blue) line shows the solution for the single corridor and the lower (pink) line
shows the double corridor. Please note that the difference between both options is excessively
because the y-as starts at € 620/gfa.
Being able to produce this result in a quarter of an hour is not the aim of such an assessment,
although it is useful. The awareness starts when students have to analyse the explanations for
these figures. One of the underlying assumptions is that elevators and staircases are placed in the
mid section of the double corridor office in order to have as many as possible office rooms using
daylight. This explains why Svinsk does not produce a result for the 10 floors double corridor;
there is not enough space in the mid section left over to put in all the elevators and staircases, a
well-known problem in designing high-rise. The option to use the mid section fully in the double
corridor situation with the low number of floors is depending of the specifications. In many cases
it will not be allowed to put workplaces in this area and modern offices do not require that much
archive space.
The lines are not fluid, which is caused by the fact that all kind of regulations, which are
taken into account, are not fluid either. One of the reasons the number of staircases is increasing
when the number of floors is decreasing is because the length of the building is escalating. So,
because the distance between office room and the staircase is limited the number of staircases is
rising. Of course much more can be said over this simple assessment. Perhaps the most
rewarding conclusion will be that in many cases the optimum number of floors will not be
realized due to the fact that building regulations for a certain area are requiring a minimal or a
maximal building height. The reasons for such regulations may be obvious in the view of urban
design, but due to this preference architects may be forced to create expensive buildings.
Architecture in Delft is given with focus on the spatial occurrence. This results in sufficient
‘natural’ understanding of quantities as walls, floors and openings. Even finishing may be valued
properly. Structural costs may cause already some problems, but it becomes really difficult to
comprehend installations and their costs. Although most of the element costs are still based on
gfa-relations, the additional value is the possibility to reflect on qualitative selection of a moredetailed level. While at one hand most application used in the early stage will stop at calculating
costs per square metre for ‘mechanics’ or ‘electrical installations’, and at the other hand exact
quantifying of ducts and apparatuses is not possible without consultation of the specialists,
Svinsk supplies costs at the sublevel like heat distribution and air treatment with the fashionable
solutions.
Table 1. Options for air treatment with the usable area of 4.000 m²
Options air treatment Quantity Costs per quantity Costs per element
Natural ventilation 5530 m² 0 0
Mechanical ventilation 5530 m² 36 198.900
Pre-treated mechanical ventilation 5530 m² 80 443.200
Air-conditioning 5530 m² 275 1.519.900
The estimate for the procurement should be based on ducts and apparatuses, but during the
design process a gfa-based cost is more logical because also the final cost will be set based on
the number of square metres, which has to be treated.
While the costs of the choice for mechanical installation instead of natural ventilation could
get an immediate adequate answer, one still could wonder if the air quality is well defined by this
choice. If used as a designer instrument, one should be aware of the fact that defining quality by
measurable parameters like technical specifications and economic conditions seems desirable,
but is still a surrogate for the full context (Gerritse 2005). There are still so many other aspects of
air treatment, which are not covered; a more accurate and time-consuming approach on costs is
not feasible at this point of design.
Working with sophisticated cost models and students, lacking the day-to-day struggle to get
proper cost information while making cost estimations, gives calculators and programmers a
double-hearted feeling: while these calculators will value the results, and the programmers will
realize the amount of work to have such an application-based model full-proof functioning for
thousands of students over the past five years, the students themselves just take it as it is, without
the required critical view on input, output and algorithms. But, beyond this feeling, it will
become a fact to deal with and in the end it will appear more the problem of the non-
sophisticated models. For educational purpose it is important to realize that working with such a
model claims an additional and all-embracing explanation of the model, in order to prevent the
appearance of a ‘black box’, with high risk of the phenomena: garbage in is garbage out.
5. CONCLUSIONS
Svinsk is proofed to be very useful as an instrument for educational purposes for the following
targets:
• Reference building
• Researching influences of qualities
• Researching effects of shape variances
• Cost awareness
• Quick results for next steps like feasibility studies
Svinsk is not aiming at learning how to make an estimate or deepening the knowledge of
element costs. For these purposes more gain will be found in estimation by hand and searchingand valuing element costs line by line. Basic knowledge of costs of building elements is much
about knowledge of construction. This kind of knowledge will hardly improve by modelling.
One of the strength of this particular model is the way in which default values are used. Even
with a few choices a full estimate is generated, while ‘adjusting the defaults’ gives an option of
fine-tuning. At this moment the research of the PARAP-group is focussing more and more on
installations. The idea is that one of the next versions will treat installations in a similar way,
enabling the quick and dirty result on installations, based on a more intelligent level then the gfa,
with at the same time the option to fill in parts of the installation, in case deliberated design
choices are possible and made. Perhaps it is necessary to recall the model is intended for the
early stage. A more final estimate will have installation costs based on the advice of the
professional in this field.
The figures in this paper may suggest the existence of an English version, but up to this point
the development is completely in Dutch. Translation into another language is easy enough, but
the core is not, although the script language is English based too. Formulas and ratios, costs,
percentages and options are bound to Dutch circumstances and building traditions. Thorough
translation will only be possible by a party with sufficient knowledge of the local market.
So, even if the result is not satisfying, with the proper tools at hand, cost calculation itself
could be fun.
6. REFERENCES
Gerritse, C. 2005, Kosten-kwaliteitsturing in de vroege fase van het huisvestingsproces, DUP
Science, Delft.
De Jong, P. (2005). Svinsk 2003, [Online]. Available from: http://web.bk.tudelft.nl/re-h/projects/
svinsk/ [14 December 2005]You can also read
