The Incidence, Causes and Prevention of Defects in the Construction of new Houses.

Abstract

One thousand cases of disputes about defects, taken from the records of the National House-Builders Registration Council, are analysed. Different types of defects are identified and quantified. Criteria off fequency, frequency/cost and frequency/seriousness are applied and the 40 most important defects identified. The causes and means of preventing these defects are considered. Quantitative patterns of the incidence of defects are given for building elements and stages, trades, cost groups and regions. The responsibility for defects is allocated to the design, site management, workmanship and component manufacture functions. The defects are analysed according to the size of builder responsible for them. The incidence of defects in builder size groups is compared with the number of houses built by the size group and reasons for differences are postulated. The defects are sorted into 11 groups such as structural, damp penetration, building movement and incomplete work. The relative importance of each group is found for different regions, geographical areas and types of complaining purchaser. Technical and behavioural factors causing differences are identified. The most contentious groups of defects and alleged defects are noted. Tolerances are proposed as objective means of distinguishing between defective and non-defective work in these groups. Schedules and check lists are built up from the analysis of defects to assist in systematic quality control of house construction. The place of the quality control function in the builder's management structure is discussed. Because all houses contain some defects, a system of demerit marking is proposed in order to define what is a defective house. The constraint of purchasers is recommended in relation to minor defects and financial sanctions against builders who do not remedy defects timeously is also recommended.