John Potter Architect | Architectural services | Design:refurbishment

Expert Witness: Investigation and Report

Expert witness: Investigation and Report.

Client: Fisher Jones Greenwood LLP, Solicitors for Apex Roofing Services LLP.

We were instructed by Fisher Jones Greenwood LLP, Solicitors for Apex Roofing Services LLP, the First Defendant, to inspect numerous slated roofs of properties at Aberfeldy, Greenhithe and elsewhere in the outer London, Essex and Kent areas. We were to comment and advise upon the suitability and fitness for purpose of synthetic fibre cement slate roof coverings. These had been distributed by Cembrit Blunn Ltd under the product name of "Zeeland" fibre-cement slates and installed on the roofs in large numbers.

Apex Roofing Services, a Colchester based company, claimed that a significant proportion, if not all, of these slates, purchased from Cembrit Blunn Ltd between 2000 and 2003, curled and lifted. It was alleged that this was caused by the inconsistent application of a weatherproof coating to the back of the slates, which led to high water absorption. This in turn forced the retaining rivets holding down the tails of the slates to be pulled straight so reducing the ability of the slates to resist wind up-lift forces. It was suggested that the absence of the coating was attributable to deterioration of the manufacturer's quality control system following transfer of production from Scandinavia to eastern Europe. The absence of the coating to the back face of the slate allowed greater water absorption to occur on the lower surface of the slate thus causing expansion and curling.

The fault first became apparent in 2003 after "Zeeland" slates fitted to properties on the Aberfeldy Estate in East London, and Ingress Park at Greenhithe in Kent, began to pull away from their rivets. Abnormal strain on the disc rivets caused them to straighten, increasing the exposure of the slate to wind uplift. This raised concerns that the slates may snap and come away from the roof. The manufacturer acknowledged that the slates could 'break and fall under uncertain wind conditions', but offered to replace only parts of the defective roofs.

The matter was transferred to the Copyright Court when the manufacturer alleged a breech of Copyright against the Contractor for distributing correspondence between the manufacturer and a third party. This therefore became a Copyright matter, rather than a Construction Court matter.

We prepared, for the benefit of the Court, a Report on the curling of the slates and the design and workmanship of the roofs on which they are laid. We also obtained further insight into the problem when the slates were wind and water tested at the BRE Research Centre. We subsequently attended Court as expert witnesses on behalf of the Claimants.

Mr Justice Kitchin, ruled that Cembrit Blunn were in breach of Contract under the Sale of Goods Act 1979, concluding that the lifting and partially lifting fibre-cement slates were 'not of satisfactory quality'. He found the evidence in support of thin and inconsistent back coating in the manufacturing process to be 'overwhelming'. The judgement can be found here: http://www.bailii.org/cgi-bin/markup.cgi?doc=/ew/cases/EWHC/Ch/2007/111.html&query=Apex&method=Boolean. The Judge found our evidence to be "... honest, knowledgeable and candid ... under cross examination and {it} has given me considerable assistance".

Apex Roofing had already replaced slates to 59 properties with an alternative synthetic slate covering and asked the Court to order Cembrit Blunn to reimburse Apex Roofing Services for the full cost of this work.

The moral of the story: be very careful when selecting slates and understand that synthetic slate coverings perform quite differently from real slate coverings. You pay your money, and you take your pick!

Below: photgraphs of the defective slates in situ, and of the BRE Test Rig upon which wind and water testing was conducted.