A NEW ROOF AT ROSSLYN

7 July 2025

From new Welsh Slate roof to a Net Zero first at Rosslyn Castle.

A historic castle in Scotland is believed to have become the oldest building in the world to have adopted air source heat pumps as a Net Zero element.

But it is at the opposite extreme of the building that another sustainable element has made its mark – Welsh Slate roofing slates as a new permanent roof over formerly ruinous areas of Rosslyn Castle’s East Range for the first time in more than 350 years.

Rosslyn Castle, jointly with Rosslyn Chapel, is one of the most significant heritage assets in Midlothian. Surrounded on three sides by the North Esk river, the castle is located within the magnificent Roslin Glen, the largest surviving tract of ancient woodland in Midlothian.

The A-listed building known as the East Range, which was completed in 1622, had remained partly ruinous since the mid-1600s. The £3.5 million project to bring the ruined areas back into use was fully funded by the Rosslyn Chapel Trust, a charity established in 1995 by the current Earl of Rosslyn, and has now won a Gold Award in this year’s Scottish Design Awards.

Its triumph was announced at “Scotland’s most prestigious awards for architecture firms and design agencies” in Glasgow on June 25th.

The trust commissioned Page\Park architects to conserve the Great Hall, adjoining tower area, and three layers of medieval vaults below, which were dramatically deteriorating due to their exposure to rainfall over the past 350 years. Historically used as service spaces, the vaults provided kitchens, bakehouses, and dungeons - spaces which are now revived as modern-day service spaces including housing air source heat pump plant rooms.

The East Range now operates as a year-round holiday let for eight people in partnership with the Landmark Trust, and income generated is used to help look after the full castle complex.

The decision to reroof the East Range was born out of a conservation management plan Page\Park undertook for the entire castle site, with one of the primary outcomes being to aid not only the long-term management of the castle but also its setting. The conservation-led approach to the project sought to minimise any visual impact on the historic setting whilst upgrading the castle and bringing it up to 21st Century standards.

Through the early stages of the design process, various options for the best approach to conserving and protecting the vulnerable masonry were considered through collaboration with Midlothian council and Historic Environment Scotland. Options included conservation of wall heads only, light-weight structures, and the reintroduction of a permanent roof. The latter option was agreed as being the most appropriate and future-proof approach, allowing for a more holistic and sustainable project to be undertaken.

While the 35° pitch of the existing roof over the East Range could feasibly be matched, this did not translate to the roofing material, which had been Scottish slate. As no newly-quarried Scottish slate was available, the project would have had to rely on reclaimed Scottish slate, and availability of this could not be guaranteed.

Page\Park required a traditional material that was local, to help the practice meet its low carbon objectives, and this ruled out Spanish and Argentinian slate which would have had to be shipped in, with high embodied carbon. Frequent users of Welsh Slate on their heritage projects, they decided to use it at Rosslyn - some 150m2 of Penrhyn Heather Blue slates to be precise.

Jonathan Walsh of Page\Park said: “Welsh Slate was an excellent alternative. The roof was a significant element of the external face of the project. We do a lot of heritage projects and we adopt the most appropriate material for each project, in this instance, natural slate to match the existing adjacent roofs.”

The Welsh slates were fitted by specialist sub-contractor B&D Roofing for main contractor John Dennis & Company (Scotland).

B&D Roofing's team included two second-year apprentices and three advanced slaters installing the Welsh slates with different widths and diminishing courses.

Site supervisor Martin Mercer said: “This project was particularly exciting due to its historical elements, requiring both pride and a high level of skill for its installation. The Welsh slates were a great alternative to a Scottish slate. I first used these slates on St Augustine's Church in Edinburgh many years ago and after the final result, with the finish and robustness of the slate, we have always advised on this as an alternative.”

The structure of the roof is expressed internally through exposed Douglas Fir rafters and linings, which echo the existing roof construction elsewhere in the building. Hidden from view on arrival, new curtain wall glazing on the west gable juxtaposes the existing stonework with a modern intervention, opening up views to the ancient woodlands surrounding the castle. From the surrounding glen below, the new glazing offers a glimpse of a new stone fireplace used to conceal structural supports for the new roof and introduce a new focal point in the ‘Great Hall’.

The castle was constructed by William St Clair during the 14th Century and has endured multiple major historical events, surviving two significant attacks. The first was by the Earl of Hertford in 1544 as part of the ‘rough wooing’ (an attempt by Henry VIII to force a marriage between his infant son and Mary Queen of Scots) which led to a period of rebuilding. This was when the East Range was constructed. It was also during this time the ‘Great Hall’ was built.

The site was attacked again in 1650 by Cromwell’s army and was so severe it left the castle in a state of ruin from which it never fully recovered. Only the East Range escaped relatively unharmed, although it is thought it was at this time the roof over the Great Hall was lost.

Post-completion, embodied carbon emissions were measured internally by Page\Park to better understand what impact the approach had and to learn lessons for future projects. The upfront embodied carbon (A1-A5) was estimated to be 174kg CO2e/m2 - extremely low when compared to the LETI 2030 targets for residential buildings at <300kgCO₂e/m2.

Rosslyn Chapel Trust director Ian Gardner added: “We are delighted to see this major and innovative project reach its conclusion. This ‘once in a generation’ work will help to conserve the East Range of Rosslyn Castle for future generations to appreciate and will absolutely transform the quality of the experience for guests staying here. We are extremely grateful for such skillful work from the contractors and sub-contractors and there is no doubt this pioneering project will secure the long-term future of one of Midlothian’s most historically significant buildings.”

James Cameron, associate director of engineering consultancy Harley Haddow, noted: “We believe that Rosslyn Castle may be the oldest building in the world to have adopted air source heat pumps as a sustainable, low carbon technology of the future.”

Jonathan added: “Page\Park are delighted to have been involved in such a unique and historic project, providing a rare opportunity to reintegrate a ruinous part of the castle into the habitable house that will help safeguard its future. As a reuse practice, we revel in the opportunity to combine our conservation expertise with transformative change in such challenging historic settings. We are proud of our role in supporting Rosslyn Chapel Trust in their vision to preserve the internationally significant precinct of buildings, providing extensive cultural and environmental benefits for future generations.”

Page\Park has a longstanding relationship with the Rosslyn Chapel Trust, having supported them in the delivery of four major capital development projects. The first, the conservation of Rosslyn Chapel, was completed in 2013, when the practice moved on to design a new visitor centre to alleviate the pressure of rising visitor numbers on the historic site. In 2018, it also completed a refurbishment of Collegehill House, a former 17th Century inn at the entrance to the site, now used as a holiday let.

< back