Under the lamp

Case study

Highgate, London

In February of 2024, we carried out a site investigation to determine the source and extent of water ingress affecting interior finishes within a converted Victorian coach house in Highgate.


Patrick Hughes


Damp Survey


February 2024



Highgate House
Highgate House

Ongoing water ingress beneath a parapet gutter to the north and flat roof area to the south had recently resulted in damage to interior finishes. Naturally, the homeowner was keen to establish both the source of the water ingress and the extent of damp affected interior finishes to resolve the issue as swiftly as possible.

As access to several of the flat roof areas and the historic northern parapet gutter was not possible at the time of survey, we utilised a lightweight drone to allow for high-level imagery to be captured and analysed. This revealed widespread cracks and fissures to the mastic asphalt finish over the majority of flat roof areas which was deemed to be at/nearing the end of its effective service life. Evidence of several campaigns of repair to the parapet gutter lining were also identified and found to have largely failed at the time of the survey leaving the structure below vulnerable to ongoing water penetration.

To the south, inadequate detailing of a suspended tile terrace over the first-floor flat roof had concealed and compounded issues of material failure resulting in active water penetration. The extent of the damage was investigated in further detail internally via the deployment of thermal imaging equipment and fibre-optic borescopes within ceiling voids.

Our team offered tailored remedial advice to inform a refurbishment strategy that was both sensitive to the historic nature of the building and practical to implement.

Using drones for high-level imagery, Six Heritage revealed critical issues with the clients roof and gutter systems that were contributing to ongoing damage to interior finishes. Our team ensured the client would have a clear understanding of the issues at hand and a comprehensive plan for addressing them, ensuring the problems identified receive the correct level of attention.

Matt Amis, Director, Six Heritage

In focus – parapet gutters

Parapet gutters have historically been a popular way of concealing eaves drainage from view to passers-by at street level. It was no surprise to find one present to the street-facing northern elevation of this Victorian coach house, though there was evidence of a history of intervention and refurbishment.

Originally, gutters would have been lined with lead, typically of a substantial thickness (modern day code 4-6, roughly 2-3mm), laid over timber boards over a sub-structure of parapet gutter joists which were mechanically fastened using butt-joints to common rafters. It was likely the majority of this build-up remained in this case, though it is important to note that lead has a long service life and is arguably better suited than modern day mastic asphalt or GRP to lining parapet gutters as failures take longer to develop.

The replacement linings present at the coach house were either poorly detailed or were reaching the end of their effective service life which left the structures below vulnerable to damp and decay. Regular inspection, maintenance and repair of all rainwater goods is vitally important, but arguably more so within parapet gutters which are not always visible to the homeowner.

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