SGT D&T has harnessed the most modern roofing materials and advanced 21st century technological know-how to help preserve one of Europe’s most remarkable ancient monuments: the 5,000-year-old Skara Brae.
This remarkable Neolithic village is a designated World Heritage Site and one of the most-visited tourist attractions on the historic Orkney islands. Hidden for centuries by layers of sand and grass, it lay undiscovered until 1850 when it was revealed by a fierce storm.
The excavated site – a fascinating commune of small interlinked stone dwellings – is incredibly well preserved, with almost everything but the roofs intact. It offers up to 60,000 visitors a year an unparalleled taste of life in Neolithic Orkney.
With the site at the mercy of the fierce coastal elements, Historic Scotland called on SIG D&T to help overcome an unusual problem.
Stephen Watt, District Architect at Historic Scotland, explained: “The dwelling that lies furthest inland on the site, House Number 7, was covered with a glass roof in the 1930s to protect its delicate fixtures, which include a collection of Neolithic stone carvings.
“Then it emerged that the glass, which protects the house from frost, water and windblown sand, was creating an unstable environment which could potentially put the carvings at risk.
“After detailed studies and research, it was decided that we needed a material that would deny light altogether if we were to provide thermal stability.”
It was crucial that any work to the 30 sq m roof blended as seamlessly as possibly with this unique natural “treasure”. Following months of appraisal, Historic Scotland selected a green roof, with Rhepanol hg, SIG D&T’s most sustainable innovation, the single-ply membrane of choice.
Rhepanol hg is a pioneering long-life waterproof membrane with unrivalled green credentials, comprising more than 70% minerals and less than 30% from oil derivative in contrast with PVC-based membranes which are mainly oil based.
This soft, flexible, thermal synthetic material, based on the proven material polyisobutylene, has been chemically improved to make it root-resistant and able to stand up to temperatures as low as -60 degress celcius. It is the only membrane to achieve the Life Cycle Assessment rating of DIN EN ISO 14040 part ff. This means it has been shown to have excellent durability, low energy consumption, low emissions and low pollutant through the whole life process.
SIG D&T’s technical team worked closely with Historic Scotland’s in-house experts to create a garden roof which closely matched the grassy slopes of the ancient site.
Stephen Watt said: “Months of monitoring and assessment went into planning the replacement roof. A temporary structure was built over the dwelling to provide protection before work began dismantling the existing roof over House Number 7.
“Part of the existing roof structure, including concrete beams dating back from the 1930s restoration work, was re-used and a series of kiln-dried Douglas fir joists fitted to provide a timber base for the new roof.”
A protective fleece layer was laid to a 22mm-thick marine plywood timber base which was mechanically fixed to the rafters. The fleece was covered with the single-ply Rhepanol hg membrane, with filter, drainage and 70mm thick growing medium layers providing a base for the sedum-planted roof.
Said Stephen Watt: “We selected Rhepanol hg because we had a duty to select a proven membrane. It’s absolutely vital we get this right because the house is irreplaceable. Rhepanol hg has a reported good track record, it’s a clean system and we expect to be able to leave the historic fabric beneath the new roof undisturbed for many years to come.”
With work complete, external views to the interior of House 7 are no longer possible, but a 3D photographic computer model is now available to allow visitors to remotely experience the interior in an intimate way not previously possible.
For more information about SIG D&T’s products and services ring (01509) 505714 or visit the website.
For details of Skara Brae visit www.historic-scotland.gov.uk.