Common 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.
Much can be learnt from the condition of the existing building stock about what mostly causes dissatisfaction after completion.
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.
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. 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 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.
Faults in New-build Housing
Similar figures published by the BRE for faults in new-build housing. 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:
Figure 3: Faults in new-build housing
Figure 1: Serious defects in existing dwellings in 2000
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:
Figure 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
Figure 4: Distribution of defects by building type
These proportions have altered since, but dwellings still predominate.
Another recent survey records that house purchasers’ complaints concerning unidentified defects in surveyors’ reports related mainly to damp – followed by damage, rot and leaks. Most frequently mentioned were roofs. Many complaints related to gas and electricity supplies.
Causes of Defects
Each volume in the BRE series breaks the figures down to reveal principal characteristics and causes of defects in each element. Advice is given on how to avoid defects, as well as on inspection and diagnosis.
For some elements, statistics are analysed in detail to show where responsibility for defects mainly lies. The overall split is estimated at approximately ten per cent to materials, 45 per cent to site work, and 45 per cent to design and specification With other elements some faults are described as due to shared or other causes, and a distinction is made between ‘rehab’ and new build.
Failings in design and specification are generally worse in rehab, where they reach a maximum of over 63 per cent in separating walls. In contrast, in new-build the failing ranges from 46.6 per cent with gas services to a minimum of 20.8 per cent with partitions.
From a review of 200 claims in the USA, causes of defects there have been broadly categorised showing that ambiguities, divergences, deficiencies, inaccuracies and typographical errors in specifications, drawings, schedules and the like accounted for just over half of all claims – making poor preparation of documents the biggest single factor in causing defects disputes.
Causes of Defects in Substructures
BRE Elements, Foundations, basements and external works states that most foundation difficulties arise from weak and compressible soils and exceptionally heavy loads. Trouble may be caused by either the imposed load or independent movement of the ground.
Approximately half of all housing substructure faults relate to cracking and settlement, one third to defective damp-proof courses and one sixth to durability of masonry below damp-proof courses. In cellars and basements, about half the faults observed related to dampness, and structural faults were few. Although its significance is uncertain, settlement is thought to affect about five per cent of all houses. Insurers of new houses report that problems associated with ground and foundations predominate in the first ten years.
Causes of Defects in Walls
Rain penetration was the most common defect investigated in external walls, at around 40 per cent of cases brought to the BRE. Entrapped water accounted for less than three per cent, and rising damp for less than two per cent; cracking was found in nearly 18 per cent and detachment in 10.5 per cent. Condensation was found in approximately one case out of ten. Nearly two thirds of all faults recorded were in new-build cavity walls. Many faults occurred at junctions with other elements.
Sound transmission and fire prevention are more significant in separating walls. Durability and satisfactory performance in terms of weathertightness, etc. was found to be significantly worse in new-build than in rehab dwellings.
Causes of Defects in Floors
The BRE believes avoidable defects occur too often. A high proportion of enquiries received by their advisory service concerns floors. BRE data suggests that about 30 per cent of all housing faults relate to floors – about two thirds of them to faults shared with other elements.
Recent figures indicate that about three quarters of floor defects relate to finishes. Especially significant are the consequences of not allowing sufficient time for concrete slabs to dry. Increased insulation requirements are again causing ventilation and cold-bridging problems – especially in ground floors. Upper floors in housing are predominantly suspended timber, and although many faults occur most are minor.
The effect on performance of faults in flooring in new housing is allocated as follows:
Figure 6: faults in flooring in new housing
Figure 5: Distribution of defects claims by cause from a survey of 200 USA engineering claims
Causes of Defects in External works
In external works, about half of all faults were in boundary and other free-standing walls, and half in pavings and drains. Drainage faults included damaged pipework and leakages, some leading to foundation settlement and some associated with pipes incorrectly carried through external walls.
Causes of Defects in Roofs
The BRE’s records show that about a quarter of all failures investigated up to around 1970 were for roofs and roofing, and that this had increased to about one third in the 1980s. Flat roof defects outnumbered pitched by more than two to one, and finishes were slightly more significant than structure. Roofing faults can lead to serious problems. Construction Quality Forum (CQF) figures indicate that a high proportion of them result in litigation. Recently, changes in insulation requirements have resulted in numerous faults relating to lack of ventilation, cold bridging, and failures to observe regulations. The BRE indicates a worsening situation with roofs.
Defects in Services
The BRE claim that most building services perform well, but that avoidable defects often occur. Their housing data gives no clear indication of how these are distributed among water, gas, electrical and other services. As has been noted, CQF data, which relate mainly to non-domestic building, allocate no more than seven per cent of defects to services, which is divided as shown below:
Figure 7: Proportion of defects which relate to service installations