A forensic investigation: Detecting multiple leaks plaguing a residential building

Location: Derbyshire
Roof type: Fibre cement slating and single ply
Roof size: 2,500 sq m
Building type: Apartment building

Roof Analytics was engaged to conduct a forensic investigation on a recently installed fibre cement slated roof of a large apartment block, plus a leaking flat roof at the same property, also installed recently. Here we describe the investigation and results.


The building owners wished to identify the causes of various leaks to different areas of the building. They also wanted to be advised on the best solution(s) to fix the problem. The leaks were located internally to the ceilings within one of the flats, at the base of a pitched valley gutter over a bathroom and to the ceilings in a corridor under the flat roof.


We carried out a forensic investigation by removing small sections of roof slating as required to study the underlying groundwork and examine the slate fixings and method of installation to establish compliance (or otherwise) with the Building Regulations, British Standards and manufacturers’ installation instructions in force at the time of fixture.

For the areas of leakage, we removed slated sections on two separate roof elevations. This offered insight on any issues that may show consistencies in application, whether good or bad, and relevant to the whole roof.

In addition to close study of these areas, we also carried out a drone survey to inspect the whole roof and establish the general quality of works. Aerial photography helps to identify any exterior defects that cannot be seen from scaffold access to the roof.


The forensic investigation identified multiple fixing errors in breach of manufacturers’ recommendations, Building Regulations, BS5534:2014 and NHBC requirements in force at the time of installation.

These included insufficient slate tail overhang, insufficient shank diameter of the copper nail fixings, the lack of tail rivets to the first course slates over the dormer roof, the lack of double rivets to the cut-double slates at the pitched valley gutter, insufficient shank diameter of the batten fixings, the lack of counter batten between the breathable membrane and the batten, and insufficient overlap of the breathable membrane. These are just some of the fixture errors we discovered, highlighting how poorly the roof had been installed, especially in the instance of the missing counter batten.


With such fundamental failures to the installation of the roof, we had no choice but to condemn it entirely for the only solution was to remove the total roof slating and associated groundwork and carry out a full replacement to the selected material manufacturers’ recommendations and all the necessary standards and regulations.

We made this recommendation to the building owners and provided a report with a written analysis and photographic evidence. The client was able to use the report as they wished – to take legal action against the installer who carried out the work or to simply ensure the roof was renewed to the correct standards.

Do you have a leak or defect on one or several of your buildings that you need to investigate? Chat to our team about a hassle-free forensic investigation. We’re happy to send a sample of one of our comprehensive reports to demonstrate the level of detail we undertake.

Lack of tail rivet on the left of a pitched valley gutter and only one tail rivet on the double width slate could result in the tail sections curling and fracturing

Abutment detail where the wider slates display only one tail rivet, which will result in eventual failure

The third course down presents as a stripe throughout the roof caused by a basic mathematical error. This compromises the headlap and is prone to water ingress.

Lack of counter batten – this hidden flaw is enough to condemn the whole roof as it doesn't allow enough space to ventilate the gap, which results in condensation.