The aim of construction cost forecasting is to provide an estimate
of a construction contract. Construction clients are interested in knowing their
fi nancial commitment before the completion of a detailed design. There are
various methods used by estimators to forecast the construction cost of building
and civil engineering projects. The accuracy of these techniques is, however,
impeded by some external factors that need to be overcome or are provided for
in order to get a realistic estimated value. This study examined the three most
common techniques used in preparing preliminary estimates in Nigeria, namely,
the fl oor area or superfi cial method, the cubic method and the storey enclosure
method. Total construction costs were extracted from the fi nal accounts of 10 bank
projects executed within the last 15 months in Lagos metropolis, Nigeria. From
the extracted costs, using a random selection, a project was used as the base on
which other techniques were used. The data were analysed using their respective
deviation from the fi nal cost and the Pearson correlation coeffi cient was used to
test their degree of relationship with the fi nal cost. The study revealed the cubic
method of calculating preliminary estimates as having the highest frequency
accuracy closest to the obtained construction value with respect to the 10 projects
sampled, whereas the fl oor area and storey enclosure methods followed behind.
However, using the Pearson product moment correlation coeffi cient, the fl oor area
or superfi cial method has the greatest relationship to the construction cost; the
cubic method came second, whereas the storey enclosure method has the least
relationship with the construction cost.

• Comparative accuracy of fl oor area, storey enclosure and cubic methods in preparing preliminary estimate in Nigeria