Welsh Slate helps save Dover mansion block from its Waterloo

Dover’s Waterloo Mansions are treated to a Welsh Slate reroof.

An unusual double-mansard roof on a Grade II listed seafront mansion block is enjoying a new lease of life, thanks to Welsh Slate.

Some 11,000 Penrhyn Heather Blue Capital-grade slates from Welsh Slate now adorn the roof and elevations of Waterloo Mansions, part of a Georgian terrace which overlooks Dover harbour, designed in the 1830s by Philip Hardwick, architect of the Euston Arch.

The multi-million pound project to refurbish the six-storey building envelope for client Dover Harbour Board was completed this summer by main contractor Walker Construction after several years, and several Covid lockdowns.

Architects Hazle McCormack Young LLP were commissioned to carry out a series of specific refurbishments/repairs to areas of the building. But the project eventually grew to encompass a full exterior envelope refurbishment to address the poor condition of the fabric and rectify some of the original design defects and subsequent poorly executed repairs/alterations that were contributing to the deterioration of the building.

Challenges included its Grade II listing which required extensive discussions and close collaboration with Dover District Council’s heritage team, its highly exposed location on the historic seafront, and resolving issues with the original design without impacting the character of the building in a Conservation Area.

Original slates taken from the roof and elevations of the fifth and sixth storeys of the older parts of the building were identified as Welsh and the specified 500mm x 300mm products from Welsh Slate were the closest match.

Project architect Nathaniel Seall said: “Some areas had been previously replaced with slates we believe were Spanish and the appearance did not match. The use of traditional materials and techniques as close as reasonably possible to the original was a key part of the project philosophy and approach taken by the client and design team.”

The upper and lower mansards are steep (up to around 72º), which affected the overlaps and some of the leadwork detailing, but the specification was otherwise mainly determined by the size and format of the original slates to maintain the appearance, as well as the exposed location, to ensure the roofing and cladding covering would be robust enough to withstand the coastal conditions.

The roof presented a wide range of features – hipped ends, several changes of pitch, parapet gutters and dormer windows. It also had to be vented below the coverings, as a layer of insulation was introduced between the timbers to improve its thermal performance. This meant careful detailing at all the direction changes – eaves and ridges, for example - to ensure the ventilated cavity was maintained but still achieving the weathering.

The slate’s main interface is with traditionally executed leadwork to abutments, parapet gutters and the roof crowns, which required careful detailing and close collaboration with the specialist roofing contractor, Butler Brothers Roofing, to maintain the ventilated cavity below the coverings. Here, the architects made extensive use of stainless steel formers to the leadwork in place of timber grounds, as this keeps these details very slim and discreet, allowing them to be incorporated without impacting the balance of lead to slate and affecting the overall appearance.

Nathaniel said: “The Welsh Slate plays a significant part in the project as the roof covering was the only element of the fabric to be fully replaced. Everything else has been refurbished or repaired in situ. It is also an important part of the overall appearance and character of the building, particularly with the slightly unusual double-storey mansard.”

He added that buying British had a role to play too.

“While the heritage connection and desire to match the original covering from a conservation point of view was the principal driver behind selecting Welsh Slate, we were also conscious of the general consensus that the longevity and robustness of a Welsh slate is superior to other options, and given the condition and scale of the project felt that this made it more appropriate,” he said.

So too did slate’s sustainability.

Nathaniel said: “As a conservation project where the material choice is somewhat pre-determined, this was not initially as much of a consideration as it would be on other projects, but we do take the overall environmental impact and carbon cost of the materials we specify very seriously, and in this respect a natural, more locally-sourced, durable, and in principle re-usable material like slate has many plus-points.

“Part of the interest in this project, and in conservation work generally, is understanding how some of the materials and techniques used in the past can be adapted to modern construction, and actually have better environmental credentials than many of the more modern, commonly-used materials we are familiar with.

“As a practice we have specified Welsh Slate in the past, principally on other projects with a conservation aspect. Often this ends up being changed as part of value engineering, unfortunately.”

Butler Brothers Roofing were 18 months on site fixing the Welsh slates on 633m² of roof with two stainless steel nails each, to minimum headlaps of 76mm (on the vertical faces of mansard) and 98mm (to roof pitches over 30°) over counter-battened sarking boards.

Director Gary Butler said: “This project was very challenging if you take into consideration the problems with updating the insulation and ventilation whilst trying to adhere to conservation rules. The specification shows the complexity of the project. But the Welsh slates performed brilliantly, as they do every time.”