cast iron pipes to BS EN 877, while considerably cheaper to supply and install than the old pipes with caulked joints, will in most situations be more expensive than PVC based systems.
COMPETITIVENESS IMPROVED
Nevertheless, the price disadvantage of the new cast iron products was less significant than expected. The study indicates that the old cast iron system was very expensive and it is to a very great extent this perception of high cost that still remains today among both contractors and consultants.
Labour constants for the BS EN 877 new pipes are dramatically reduced compared to the old systems. To an extent the EC Harris research found that the CIDDA assumptions on labour constants were correct. The established times used in the price books for making a joint in a straight run of underground drainage showed a lack of consistency between price books. One price book suggested that a metre run of 100mm diameter mechanically jointed pipe, laid in a trench bottom should take 0.55 labour hours of advanced plumber and 0.55 hours of apprentice plumber. This equates to 1.1 hours of total labour time per metre run or 3.3 hours for a 3m length of pipe. To put it another way one man would be expected to lay only 3 pipes in a working day and even then he would need to work 2 hours overtime to achieve this.
To validate the new built-up rates, contractor's estimators were approached. The perceived opinion was that the build up of rates was reasonable. One contractor came back and said that their labour constants were lower than the ones calculated in the research.
NOW REFLECTED IN PRICE BOOKS
On completion of the research, the producers of the main building prices
guide books were contacted to update their records. Davis Langdon and
Everest, producers of SPONS accepted the research and applied the new
rates to their price guides, Griffiths price guide also following suit.
The latest SPONS guide (2001), now lists labour time and costs of the
BS EN 877 cast iron systems lower than uPVC solvent weld systems which
emphasises, speed of installation of the mechanical joints.
BENEFITS
There are a number of benefits a cast iron pipe system implies. Cast iron is less likely to suffer physical damage in exposed situations and is less susceptible to damage during the course of construction work.
As mentioned previously, there are also associated benefits in terms of fire resistance and sound insulation properties which need to be taken into account when determining the competitiveness of cast iron against alternatives.
Cast iron also requires minimal maintenance and in normal use will last the full 60 years normally taken as a building's life. For clients with a long term view, cost-in-use calculations could well indicate that a cast iron system will provide an economic solution. This benefit is now being utilised in the growth of PFI projects.
COST BENEFIT ANALYSIS/RISK ASSESSMENT
When conducting a cost benefit analysis it is important to consider the issue of business risk associated with a failure of the drainage system. Clearly this takes on significant proportions in the case of revenue sensitive operations such as supermarkets, and high priority use buildings such as hospitals.
SPECIFIER TO DETERMINE 'VALUE' VERSUS 'COST'
Having recognised that the use of cast iron is likely to be more expensive than alternative materials, the key question for building owners and specifiers is of course, 'under what circumstances will it be worth paying the extra?' This involves a consideration of costs versus benefits and risk analysis.
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