At a later point, when dealing with apportionment of responsibility, his Honour said that the appellant "had within its capacity to take reasonable care by a system of regular inspection and maintenance to prevent the danger arising at all".
15 The appellant did not take issue with his Honour's statement of its general duty to take reasonable care to safeguard the customer from injury: cf Northern Sandblasting Pty Ltd v Harris (1997) 188 CLR 313, at 340, 342-3, 347-8, 365-6. It submitted that his Honour had fallen into error in three respects. First, it said that there was no evidence that water entry down a screw, as was found to have occurred on this occasion, had occurred previously - rather, the evidence identified rusty sheets of iron as the likely source of the earlier leaks, and the offending screw was in a new piece of iron. The "inevitability" of water entry in the particular manner was, it said, an erroneous basis for what followed. Secondly, it said that in insisting on a system of regular maintenance and inspection his Honour had misapplied the "ordinary principles of negligence" in Wyong Shire Council v Shirt (1980) 146 CLR 40, and had in effect imposed strict liability on the appellant. Thirdly, it said that in any event it had not been established that employment of a proper or better system of regular maintenance or inspection would have detected the source of water entry or the water entry, so as to preclude the presence of the water in which the customer had slipped. Causation had not been shown, at least unless the system of regular maintenance or inspection would have led to discovery of the problem with the screw, and there was no evidence that it would have.
16 For present purposes I am prepared to assume that, as his Honour said, the seal waterproofing a screw holding roofing iron can break down so that there can be water entry down the screw, even that breaking down in relation to some of the screws in a roof is inevitable. In my opinion, however, the appellant's submission in other respects should be upheld.
17 In Wyong Shire Council v Shirt, in a passage which has often been adopted and applied, Mason J said (at 47-8) -
"In deciding whether there has been a breach of the duty of care the tribunal of fact must first ask itself whether a reasonable man in the defendant's position would have foreseen that his conduct involved a risk of injury to the plaintiff or to a class of persons including the plaintiff. If the answer be in the affirmative, it is then for the tribunal of fact to determine what a reasonable man would do by way of response to the risk. The perception of the reasonable man's response calls for a consideration of the magnitude of the risk and the degree of the probability of its occurrence, along with the expense, difficulty and inconvenience of taking alleviating action and any other conflicting responsibilities which the defendant may have. It is only when these matters are balanced out that the tribunal of fact can confidently assert what is the standard of response to be ascribed to the reasonable man placed in the defendant's position."
18 Mr Olney had extensive experience to do with roofing, and had attended to the roof of the shopping centre over a period of about six years. He had been called on to ascertain the source of a leak in a roof hundreds of times. He described how that was done, in brief by seeing where water was running down a beam or a truss and if it could not be traced in that way by putting a dye colour on the roof and seeing where the colour came in, and -
"Q. Can we summarise that by saying that when tracing the source of a leak one follows the water?
A. Yes you can summarise that, that's the way of finding a leak in a roof.
Q. Is it possible to find a leak in a roof of a kind that was above Grace Bros section of the shopping mall in the absence of water to trace?
A. I can't say no, because nothing is impossible with all due respect, but it's very improbably [sic] because you have to be advised a leak is there before you go look for it, and the only way you're advised a leak is there, is it's leaking and there's water coming through it. It is possible to seal roofs prior to a leak, but that's an extraordinary cost that people just don't go to. The standard way of finding a leak is when there's water and it leaks, and you follow the trace back. And you can go to a lot of other problems if you want me to explain, but I mean it's a lot of cost.
Q. In your years of tracing the source of leaks, have you ever employed any other technique than following the water to the source?
A. No we've suggested it to some RSL Clubs, but they are not interested once you tell them the cost, they're happy to wait until they find a leak and go with it from there."
19 This evidence was uncontested. It was not suggested to Mr Olney, or the subject of other evidence, that leaks in a roof of the kind presently in question could be detected ahead of time by inspection, that maintenance of a roof would include detecting and obviating a leak of the kind presently in question in the absence of water entry to trace, or that a system of inspection and maintenance was either normal or something which could usefully be put in place at reasonable cost. Mr Olney's evidence was that sealing roofs prior to a leak, by which in context was meant finding a leak in the absence of water to trace, was an extraordinary cost, a cost "that people just don't go to".
20 The water entry presently in question was down a screw securing a new sheet of iron. The respondent's case was not of negligence in fixing the new sheet of iron, nor was it of negligence in having leaky old iron on the roof. In the balancing of which Mason J spoke the "expense, difficulty and inconvenience of taking alleviating action" was in instituting a system of maintenance and inspection in order to detect and obviate a source of water entry down a screw. On the evidence of Mr Olney, there was both little prospect that a system of maintenance and inspection would be sufficient to detect such a source of water entry, and an extraordinary expense of such a system in an endeavour to do so, to balance against the magnitude of the risk to entrants to the premises and the degree of probability of its occurrence.
21 On the other side of the scales in the balancing exercise, it was correct to envisage possibly severe consequences to a person slipping in water on the floor. But the risk was lessened by the expectation, although of course not a guarantee, that the occupier of the premises would detect any water entry and take steps to clean it up, and would erect barricades to prevent slipping in the water while the source of the water entry was detected and rectified. That is why it could have been material to investigate why the respondent was liable to the customer, but that was not done. Even in relation to common areas of the shopping centre, a procedure could have been put in place to guard against occasional water entry leading to injury.
22 In my opinion, his Honour should not have held that the appellant was in breach of a duty of care owed to the customer. I do not think that a duty of care owed by it as lessor of the premises to entrants to the premises required that it go to the extraordinary expense, so far as the evidence showed not an expense which would necessarily have detected and rectified a source of water entry of the kind presently in question ahead of the entry of water, of something more than the ad hoc approach; and what that could have been was not disclosed.
23 Even if this be incorrect, in my opinion there was no evidence on which it was open to his Honour to conclude that, if a system of regular maintenance and inspection had been in place, it would have detected ahead of time the source of water entry presently in question. The only material evidence was that of Mr Olney. It gave no support to a system for detecting that water would leak from the roof surface down the screw. He was not asked what could have been done to "seal roofs prior to a leak", or to explain what he meant by "or you can go to a lot of other problems"; he was not asked what had been suggested to the RSL clubs. The respondent pointed to his evidence to the effect that, in order to trace a leak which was not still leaking, more water could be put on the roof, but that was evidence directed to a known leak the precise location of which was to be found. It was not suggested to Mr Olney that a system of maintenance and inspection could have been putting water on a roof greater in size than a football field in order to see whether and where there might be water entry.
24 The leak in question was in fact traced by Mr John Rogers, a plumber summoned by the respondent, who went into the ceiling and traced the leak to the screw, and then got up onto the roof, pulled the screw out, and replaced it with a silicone sealant. Mr Rogers said that the screw could have been loose, but he could not remember whether it was. As I have said, it was not shown that the earlier water entry coming to the particular place within the premises had been from the screw.
25 Even if the appellant had been in breach of a duty of care owed to the customer, it would not have been liable to the customer unless the breach caused or contributed to the customer's loss, and so it had to be established that having in place a system of regular maintenance and inspection would have precluded the water entry which caused the customer to slip: cf the need to establish that a proper or better system of cleaning would have prevented the slipping in Sleiman v Franklin Food Stores Pty Ltd (1989) Aust Tort Rep 80-226 esp at 68,834-5. There was no evidence that such a system would or might have detected the unsatisfactory sealing at the particular screw, no doubt one of thousands in the roof. I do not think that was established.