Roof renovation at St. Mary's Cathedral in Andernach
The Roman Catholic church of the Assumption of Mary is an impressive building. The mighty gallery basilica with its four towers, west building and choir is located in the immediate vicinity of the city walls of Andernach. This is where the fort of Antunnacum was located in Roman times, from which the later settlement developed. During work next to the church in 2006, the remains of a Roman bathing complex from the 4th century were even discovered, proving the historical significance of this location.
The history of St. Mary's Cathedral goes back far into the 12th century. Little is known about its original appearance, but Carolingian grave sites under the present church indicate a very early foundation. As early as 1194, the previous building, at that time still St. Michael's, was donated to Archbishop Johann I.. This building fell victim to a dispute over Andernach in 1198 and was destroyed by fire. All that remained was the free-standing bell tower, which has survived to the present day. It is assumed that the church was consecrated in 1220.
In 2019, just in time for the 800th anniversary of the building, the roofs of both west façade towers were due for renovation. So a working and protective scaffold had to be erected for the two towers with a height of almost 50 metres. The contract for this was awarded to the scaffolding company Schmiedt from Kobern-Gondorf, which has made a name for itself nationwide with outstanding scaffolding solutions on numerous buildings. In addition to many historical buildings, castles and churches, the company also provides solutions for new buildings and for the renovation of modern structures.
Scaffolding of this dimension always requires a static calculation. This is because both the scaffolding construction itself and the difficulty of anchoring it in the historical masonry require an engineering approach. In such cases, Schmiedt works closely with the engineering and expert office for scaffolding construction IBS, Dipl.-Ing. Joachim Specht & Partner. Responsible for this project was Manuel Specht, who planned, calculated and also supervised the demanding scaffolding construction during the erection phase.
It was quickly discovered that the wooden roof truss was still the original 800-year-old wooden construction. Of course it had to be preserved, so a weather protection roof had to be installed in addition to the scaffolding. So the scaffolding was unceremoniously braced in order to make it load-bearing for the aluminium cassette roofs over the upper 20 m, where it could not be anchored in the cathedral wall.
With regard to the scaffolding technology used, Gerüstbau Schmiedt relies on systems from Scafom-rux, a manufacturer of modern scaffolding systems with over 60 years of experience as a partner and supplier to the scaffolding industry. Essentially, the Rux-Variant modular scaffolding was used for the scaffolding structure, as well as the Rux-Alu-Rasant cassette roof for the weather protection roof above the two towers.
In addition to the area susceptible to wind forces, a factor that always needs to be taken into account with scaffolding of such dimensions, there were two other major challenges for those involved that had to be solved in terms of engineering. On the one hand, there was the fact that the scaffolding on the towers could only be based on two sides. On the other hand, a platform had to be erected between the towers from a height of about 24 metres up to a height of 30 metres, which connected the two scaffolds and served to store material and equipment. This platform had a span of just under 10 metres.
Since the towers had to be scaffolded from all sides in the so-called “pinnacle" area, but could only be erected on the ground on two sides, elaborate steel and lattice girder structures were required from a height of around 26 metres, which partially went through the towers themselves to enable the massive scaffolding construction to be accommodated on each of the two sides. In addition, double standard supports were fitted in the lower area of the scaffolding, both inside and outside, in order to absorb the immense load of the entire structure. The fact that the roof structure of the central nave could not be stressed and exposed to loads added to the challenge. In the area of the two roofs, the scaffolding construction was adapted to the roof slope with the help of 2-plank brackets so that the various trades could carry out their work without danger.
Far more than 3,000 square metres of Rux-Variant scaffolding material as well as several running metres of lattice girders and scaffolding tubes were installed on the object. With the help of a truck-mounted crane as well as various lifts - two of which were placed on the platform between the towers - the material was transported safely and economically to the appropriate places by the Schmiedt company.
A stair tower with aluminium stairs was erected for safe scaffold ascent and convenient transport of material and tools for the subsequent work by the trades. Furthermore, the lifts used to erect the scaffolding were also available during the renovation phase.
Actually, a varied anniversary programme was on the calendar for 2020, which was also pointed out by a large banner on the scaffolding during the construction phase. But here, too, the Corona pandemic has thrown a spanner in the works, so the celebrations will probably have to be somewhat smaller or postponed. The important thing is: the towers shine in a new splendour and the completed work gives hope that the Mariendom zu Andernach will survive another 800 years.
Gerüstbau Schmiedt can add another prestigious object to its list of references - an extremely successful interplay of various agencies that are not only highly skilled in their fields but also have a soft spot for historical buildings. Christian Schmiedt, who is responsible for the planning, says enthusiastically: "A 50-metre church tower is already a challenge. But a double tower with a stage in between and two weather protection roofs on a free-standing scaffold as the crown ... that's a unique combination - it really gets your heart pumping".