It is worth looking at the judgment of Windeyer J as he draws a distinction between the word “fault” as something blameworthy or “fault” as the word is used in the particular clause as being a description of an inanimate thing; and the use of the word “faulty” in that sense means defective, namely, bad in any respect not fit for the use intended. He contrasts this, however, with the exclusion relating to faulty workmanship which he takes to be a reference to fault or something done wrong on the part of the workman. He continues by saying that if the words had been “faulty designing” then the two phrases would have been comparable.
This analysis was accepted by the Court of Appeal in Hitchins (Hatfield) Ltd. v. Prudential Assurance Co. Ltd.  2 Lloyd’s Rep 580. It was held that the phrase “defect in design” did not require negligence although “defectively designed” did require proof of negligence to enable the insurer to rely on the exclusion.
In Kiev Construction Ltd. v. Royal Insurance (UK) Ltd. & Ors.9 30 Con. LR 45, the assured made a claim for damage to temporary piles constructed in the course of building works at the nuclear power generating station at Sizewell B. The claim was made pursuant to a single site construction all risk policy. The policy excluded “works … defective in material workmanship, design or plan…”
The court held that, in the circumstances, there had been no negligent workmanship in that the damage was most probably caused by unusual ground conditions not readily foreseeable, although it was recognised with the benefit of hindsight that the work could have been carried out differently.