Defective Building Materials?

Ultimately, defects in materials may be regarded as arising in poor design or workmanship.  It is arguable that a material itself cannot be faulty, only incorrectly used.  For example, using green, rotting or damaged timber for floor joists will result in faults in the floor after construction.  Neither a competent designer nor a skilled worker would select such timber where dimensional stability and durability were required; it is incompetent action that causes the building defect. 

Paradoxically, the careful selection of flawless timber may give rise to an allegation of faulty materials. 

Some 25 years ago, the following problem was encountered in a new terraced housing development in Milton Keynes:

The floors had been designed so that the living room floor joists were at their maximum spans.  The contractor, a cautious and conscientious man, carefully selected knot-free timber for the longer spans.  On completion, these floors were disturbingly mobile.  People crossing their living room floors excited resonant oscillations, causing furniture at the edges of the rooms to hop gently towards them.

The floors were moving safely within their elastic limit and were acceptably level under dead load.  However, the knotty joists, which were so carefully selected out, would, if left in, have randomly stiffened as well as potentially weakened the floor. 

In the above example, the joists had been carefully selected to be the ‘best of their respective kinds’.  The structural design, as an exercise in applied mathematics, was correct and accorded with published guidance.  The floors were not ‘fit for purpose’ because footfall caused unacceptably large resonant oscillations. 

The materials were blamed for the fault, in that they were insufficiently stiff to provide stability, although considered solely in terms of the quality of the material the living room floor joists were consistently the best of the structural timbers used in the building!

Defects often arise because the designer does not consider how materials will behave during construction and during the life of the building.

It is fundamental to good building practice that the design takes into account the process of construction.  Concrete, for example, is unlikely to be built as a monolithic mass.  Each part of a concrete structure will be limited to that which can be built in a single working day.  If the inevitability of day joints is considered in the design, their effects on strength can be controlled.  It is less certain that their effect on the watertightness of the concrete can be controlled, but good design – which takes into account construction techniques – can greatly reduce the risk of impaired performance.

Good communication between designers and building workers helps to resolve problems.  Some designers’ lack of practical knowledge is all too apparent to site staff when they are asked to work from ill-conceived drawn details.  This encourages building workers to pay scant regard to detailed designs and to implement their own ideas of how to build, working round what they see as bad designs rather than discussing them with the designers.  This is particularly common in design-and-build contracts where the builder stands to gain no contractual advantage from drawing attention to design defects.

During an investigation of a dispute between a Dutch contractor and manufacturer over a new partly built factory, the project engineer’s drawings were studied.

Part of the ground-bearing concrete floor slab had been carried down to form a lift pit.  The drawings showed asphalt tanking to the outside of the pit walls and floor.

Had the work been built to the drawing, it would no doubt have performed adequately. 

The problem was that the asphalt would have had to be applied to the concrete after the concrete had been formed.  As it was to be applied to the outside of the concrete, this would have involved sending in a team of miners to tunnel under the lift pit with picks in one hand and buckets of steaming asphalt in the other.   As this seemed somewhat unlikely, the site agent was asked to explain what he had built. 

His immediate and firm answer was that he had built precisely what was drawn.  With proper acknowledgement of the admiration due to the mining skills of the asphalters, the impracticability of building what was drawn was spelled out to the site agent.  He immediately changed his story and claimed he had recognised he could not build what was drawn and had obtained revised instructions from the engineer, which were, of course, fully recorded, he said, in his site instruction book.  Invited to show the revised instruction, he spent some ten to fifteen minutes thumbing through a handwritten journal without success.

It was impracticable to build the detail as drawn.  The lift pit had not been tanked.  The contractor was in breach of contract but, at the source of the problem, was the failure of the designer to consider how what he had drawn was to be built.

If the design doesn’t permit building in a logical sequence it is not likely to be followed

 

As well as the worsening of communication caused by the often shifted sands of truth on a building site, the above problem illustrates the potential pitfalls of isolating the designer from site work.  This can militate against both a good understanding of what is buildable and close co-operation between designers and site workers.

The best design is of no value if workmanship is inadequate.  Good design assists workers but it does not prevent errors on site.  Site supervision and inspection can catch bad work but it cannot create good work.  Skilled tradesmen cannot safely be replaced by unskilled workers no matter how good inspection and supervision.