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 finishing
given 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 by
the 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 the
calculation 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 space
and 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 more
detailed 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 searching
and 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]
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