1
Ex ante performance evaluation of housing
Methods and tools
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André Thomsen |
1.1 Measuring performance.................................. 285
1.2 Measuring functional quality........................... 285
1.3 Measuring costs................................................ 286
It is well known that the first stage of the design
process enables the maximum adaptability of the plans but disposes of the least
information. Towards the final realisation of the building the information
about the performance grows to a maximum and the adaptability diminishes to
almost zero. It is therefore essential to achieve results of performance evaluation
as early in the design process as possible. Ex-ante performance evaluation
proofs to be a useful approach for that purpose. This kind of ex-ante
evaluation is based in principle on anticipation on future performance using
broad and long term experience with similar products. This makes it useful for
application on serial produced housing projects.
However some major difficulties are to be
solved, regarding measurement and assessment of performance as well as
practical utilisation.
1.1
Measuring
performance
For performance evaluation a large number of
methods is available, varying from post occupancy evaluation and user enquiry
surveys to various kinds of benchmarking. Most often they are based on
quality/cost rating. For early design and development stages simple and ready
to use quality/cost rating-methods are most suitable. We will discuss the use
of both variables: quality and cost, as follows.
1.2
Measuring
functional quality
The performance of housing products depends
mainly on the satisfaction of the residents, as this determines the market
position of housing estates. Resident satisfaction depends upon a mix of mainly
functional qualities (e.g. usable floor space) and subjective preferences (e.g.
location). Though quite some research is available regarding resident satisfaction,
the translation and implementation of functional users preferences in
evaluation criteria of built construction come across a couple of problems:
The translation of functional preferences,
based on dwelling activities, in building construction characteristics. For
instance: the activity cooking (of a meal) implicates not only functional
criteria for the kitchen floor plan and equipment but also for heating,
ventilation, relation to dining room/table, to be differentiated depending on
household type and size etc.
The implementation of a large number of incomparable
and partly contradictory aspects in a useful and practicable system.
Solving this problem encounters a dilemma. One
has to choose between very complicated compiled scorings, leading to insignificant
non-transparent results, and simple but questionable undifferentiated results.
As a research project targeted at the development of a consumer’s test for
housing products showed though, a useful and practicable system like the Dutch
Woning Waarderings Stelsel (Dwelling Assessment System) is largely favourable,
as it is widely used and recognised as a comparison gauge (Thomsen 1992, 1995).
Regarding its nature quality assessment must always be considered to be a rough
and doubtful approximation of the many facets of the reality.
1.3
Measuring
costs.
Though most often used in building construction
practise, investment costs are not practicable for assessing performance,
optimisation and weighing alternatives. Running costs like maintenance, energy and
management costs should be considered as important as the initial building
costs. To compare different (re)design and (re)development alternatives a Life
Cycle Costs approach using net present value is necessary (see Ruegg and
Marshall, 1990)
Methods and tools
In recent years a variety of design and decision-making
tools have been developed based on some kind of quality/cost assessment (Van
der Flier & Thomsen, 1996, van den Broeke, 1998). They are to be used for
ex-ante performance evaluation in the early project development and design
stage. They focus on different levels of scale: product-level, neighbourhood-level
and company/local-level, and different purposes: analysis, strategy development
and assessment. Table 1 shows the relation between them in the routing of
project- (and policy-) development.
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Table 1: Routing of
project-development.[1] |
Most of these tools are software applications
developed for building and planning consultancy. They calculate integral life
cycle costs to compare with qualitative variables, resulting in a performance
score. Though practical for quick scan and weighing alternatives, the
qualitative variable is the weak component. This can be seen, for instance, in
the rather sophisticated Anymo-system (Van Leent et al., 1992). It is developed
as computer software for portfolio analyses of rented dwellings. The system
evaluates the market position and performance of the dwellings. Basic determinants
are the quality and the rent. Input data are quality aspects, derived from a
list of criteria, and scored by a panel of managing staff and or surveyors.
Based on the quality score the potential gross rents and assets are estimated.
The system is clearly market- and product-oriented and may best be applied for
weighing alternative interventions regarding the market position of dwellings.
The weak point of these market-oriented systems is the fact that
market-indicators are rather soft and fluctuating; often they are just symptoms
for deficits that could be neglected in the decision making.
2Conditions and restrictions
Using these tools we should keep in mind some
conditions and restrictions. According to Potting et al (1990) the tools may be
reviewed referring to the following initial goals:
·
rational
basis for decisions
·
efficient
use of resources
·
transparency
of effects
·
open
democratic decision control (discussion of this goal is beyond the scope of
this article)
·
use of
professional skills
The tools are meant to offer a rational basis
for decision making on programs and plans. As we have seen above the
qualitative variable is often a weak point. And apart from that: ratio is not
the only ground for decisions. It is wise to take into account that assessment
of alternatives in practise is influenced by a lot more often ‘irrational’
items than people like to admit.
The tools should enable a more efficient use of
budgets and resources. But the use of these tools is a matter of optimisation: a
rather good decision is not enough, one perfect solution does not exist and
there is often more than one good alternative.
The tools should give a transparent view of the
design process and the effects of programs and plans. This presupposes the
presence of proper professional skills (see below). They are expected to reduce
the complexity of decision making but the result can be a false simplification
of reality. Weighing alternative should be based on comparable and realistic
conditions or programs.
The tools should make use of professional
skills. The selection of relevant information and parameter values is a matter
of profound professional knowledge of housing management and economics and is
therefor the most tricky part of the system. This includes a minimum of
comparability and knowledge of use and misuse of evaluation methods (Lans,
2000). Systems for experts may also be used to hide the absence of knowledge
and skills, or worse: to generate and proof desired results. Also for this it
is essential to keep an open and controllable check on input, throughput and
output.
Ex-ante performance evaluation of dwellings
implies the reduction of doubts. The design and decision tools can help to
diminish uncertainty and sharpen the awareness for risky elements. But even the
smartest tools cannot give a guaranteed well performing solution.
3Bibliography
Broeke, R. van den, 1998, Strategisch voorraadbeleid van woningcorporaties: informatievoorziening en instrumenten, (DUP), Delft.
Flier, C.L. van der, en A.F. Thomsen, 1996,
"Matching alternatives, Design & Decision Support Systems for the
management of existing housing stock", paper for the Int. Conference on
Design & Decision Support Systems in Architecture and Urban Planning, Spa
1996.
Lans, W, 2000, “Housing evaluation, some
methodological considerations”, in: proceedings, ENHR 2000 Conference, Gävle.
Leent, M van, en J.M. van Vliet, 1992, Strategisch woningbeheer, systematiek en hulpinstrumenten van DHV Bouw bij het opstellen van beheerplannen, DHV, Amersfoort.
Potting, A. en M. del Canho, 1990, Behelpen als hulpmiddel, Afstudeerscriptie Faculteit der Bouwkunde TU Delft.
Ruegg, R.T. and H.E. Marshall, 1990, Building
economics, Van Nostrand Reinhold, New York.
Thomsen, A.F., 1992, "Towards a consumers
test for houses, surveying users-preferences and functional quality", in:
proceedings, International Research Conference on Housing, Montreal,
2/7-07-1992.
Thomsen, A.F., 1995, "Woonconsument en woningkwaliteit, prestatiemeting van woningen met behulp van vergelijkend warenonderzoek", in: "Tijdschrift voor de Volkshuisvesting", vol. 1 nr. 4.