The Pathology of Building Defects
The incidence of different types of defects
What is a Non-defective Building?
In the most general sense, a satisfactory building is one which is where it is needed, fits appropriately into its surroundings, and provides adequate space and facilities, protected from adverse weather and other undesirable external conditions. Since this protection cannot readily be achieved with short-lived structures, buildings typically outlast many other modern products, and, if built so that they can be adapted to changing requirements and easily repaired, can give satisfactory service for a long time.
Condition Surveys
Much can be learnt from the condition of the existing building stock about what mostly causes dissatisfaction after completion.
Dwellings
Existing buildings in Britain number about 25 million. Most are dwellings, which in 2000 numbered about 23 million – well over 90 per cent of the total, but it is estimated that in terms of floor area, domestic and non-domestic buildings are roughly equal.[1]
At the beginning of the 20th century there was, in Britain, one dwelling for every 2.6 persons – slightly above the size of today’s dwindling average household. Population growth is now slow overall, and current demand for building arises largely from changes in household composition and inter-regional migration. The annual rate at which new dwellings were being completed in 2000 had fallen to well under 200,000, compared with more than double that figure in the mid 1960s.
Consequently, for English houses as a whole, recent official figures indicate that more than one fifth are over 80 years old, and around half are 50 years old.[2] There are no comparable statistics for non-residential buildings.
In spite of their age, most existing buildings are still fit for continued use. Government statistics for dwellings officially designate as unfit less than 5 per cent of the total (i.e. 885,000 unfit dwellings). The most common reason for unfitness is disrepair (46%), followed by facilities for the preparation and cooking of food and dampness. Externally, faults occur most commonly in roof features and rainwater goods (34%), exterior wall finish (26%) and windows (25%). Internally faults are most common in ceilings (22%). This is an increase in the number of houses which are in disrepair when compared to the previous year’s survey.
Incidence and type of faults is given in figure 2 and as follows:
no faults 31%
interior faults only 6%
exterior faults only 35%
both interior and exterior faults 28%
Other official publications[3] give some indication of the maintenance required. For housing, in terms of maintenance cost, external walls accounted for 13 per cent and windows and doors for 14 per cent. In about six per cent of dwellings, rising damp had affected internal walls and partitions.[4]
Faults in New-build Housing
Similar figures published by the BRE for faults in new-build housing.[5] External walls and roofs each account for about 20 per cent of total faults, doors and windows for up to 18 per cent – a total average for the external building envelope from surveys in 1980 and 1990 of some 58 per cent. The biggest elements of internal works are: services, separating walls, partitions, upper floors and ceilings. Substructure, ground floors and damp-proof membranes together make up less than three per cent. External works add up to about two per cent and miscellaneous defects account for the roughly ten per cent remaining.
These figures are set out in greater detail in the BRE series on building elements, which is based on several decades of defects investigations. The volume on walls, windows and doors indicates that, of the defects investigations carried out in the 1980s by the BRE, over half were into dwellings. The distribution among building types is shown in the following chart:
Fig 4 Faults in new-build housing
Fig 1 Serious defects in existing dwellings in 2000
Non-residential Buildings
Comparable statistics for mainly non-residential properties can be found in the database managed by the Building Research Establishment (BRE) for the Construction Quality Forum. In 1997, the occurrence of defects by element was shown to be as follows:
Fig 2 Occurrence of defect by element in mainly non-residential properties
From this it will be seen that defects in external elements are over half of the total, and that, with adequate maintenance and the upgrading of services and installations, most buildings could probably last a very long time.
Distribution of Faults by Building Type
Fig 3 Distribution of defects by building type
These proportions have altered since, but dwellings still predominate.
Another survey records that house purchasers’ complaints concerning unidentified defects in surveyors’ reports related mainly to damp – followed by damage, rot and leaks.[8] Most frequently mentioned were roofs. Many complaints related to gas and electricity supplies.