Persistent water ingress into a live office space had remained unresolved for over two years, despite multiple attempts by others. Through controlled dye testing and targeted investigation, the true source of the leak was identified and resolved without the need for full roof replacement. This case study outlines the process from diagnosis through to successful outcome.
The Problem
We were instructed by BNP Paribas Real Estate to investigate ongoing roof water ingress affecting a seventh-floor terrace above a live office space at Trinity, Manchester.
The issue had persisted for approximately two years. Multiple attempts had been made to resolve the problem by the original waterproofing manufacturer and other contractors, including flood testing of the balcony area and localised sealing works to the balustrade and perimeter details. Despite this, the ingress remained unresolved.
Given the disruption to the tenant below, it was essential that the cause of the ingress was accurately identified before any further remedial works were undertaken.
Diagnosing the Source of Roof Water Ingress
A detailed inspection of the terrace was undertaken, during which all potential defect locations were reviewed. This included assessing the falls across the coping stones, which were found to direct water back towards the termination detail.
The balcony waterproofing comprised a ballasted single ply system, which by its nature can allow water to track beneath the surface layer.
To accurately diagnose the issue, controlled, non-destructive roof leak testing was carried out using coloured dyes. The terrace was divided into zones and tested systematically, allowing the movement of water through the construction to be tracked.
This approach confirmed that water was not entering through the primary waterproofing membrane, but instead through joints in the coping stones and at the interface between the coping stones and the termination detail, before tracking beneath the waterproofing layer.
Identifying the Cause
The testing demonstrated that:
Water was entering through joints within the coping stones
Moisture was tracking behind the termination detail
This type of interface detail represents a high-risk junction, combining:
movement
multiple materials
mechanical fixings
and reliance on sealants
Developing the Solution
A full roof replacement was not considered necessary or proportionate.
Instead, a targeted remedial strategy was developed, focused on addressing the identified failure points.
The agreed solution involved:
Installing a reinforced liquid-applied waterproofing system over the coping stones
Integrating balustrade penetrations into the waterproofing layer
Introducing a trim detail independent of the existing membrane system so as not to affect the existing guarantee
Selecting a system that would provide a suitable aesthetic finish, noting that the seventh-floor tenant is an architectural practice and appearance was an important consideration
Care was taken during specification to avoid preparation methods that could worsen the issue. In particular, jet washing was avoided to prevent introducing additional moisture into an already vulnerable detail.
Installation
The works were carried out by Holloway Cook, with technical input from Polyroof.
Preparation, detailing and coating application were undertaken in stages, with independent inspections carried out throughout the process.
The final finish was completed using a grey topcoat, following initial trials of a sandstone colour which was not considered visually suitable.
Outcome
Following completion of the works at Trinity, Manchester, the site experienced significant rainfall, providing a real-world test of the repair.
A final inspection confirmed:
No evidence of water ingress into the occupied space below
Internal areas previously affected remained completely dry
The waterproofing system appeared continuous and well executed
Feedback from the occupants confirmed that the issue had been resolved.
Client Feedback
“We approached Steve Cookson to provide technical advice on an ongoing and challenging case of water ingress into a live office space. Previous surveyors had attempted to deal with the issues with little or no success. Steve was not only sensible in his approach, but kept us informed at each step, providing written updates that could be shared with all interested parties.
After identifying the likely cause Steve worked with a roofing contractor to provide a solution which was tendered and instructed. The works were undertaken and the solution has provided a successful outcome.
I wouldn’t hesitate to recommend Steve Cookson to anyone having issues with water ingress via their roof, and we have already requested Steve Cooksons services for his input on another project.”
— Ian Porter, BNP Paribas Real Estate
Key Takeaway
This project demonstrates the importance of professional roof leak investigation and targeted waterproofing design, particularly where complex interface details are involved.
At Trinity, Manchester, a structured approach combining inspection, controlled testing and precise remedial design resolved a long-standing issue without the need for full roof replacement.
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