Material Marvels: The Notre-Dame fire highlighted timber shortage issues

Materials World magazine
10 May 2019

Policies, trade partnerships and politics can all influence what trees are available to harvest. What happens when the best timber is not available?

Finding the appropriate timbers that can be applied to specific applications is an ongoing issue. For Notre-Dame, sourcing timber that matches the original used in the cathedral will be difficult, to stay the least, as France no longer grows such trees.

The UK imports about 70-80% of its timber requirements, with the remainder coming from home-grown sources – a ratio that has more or less stayed the same for the past couple of centuries. This imbalance is due to the UK lacking the land availability required to grow enough trees to meet demand.

A growth industry

Oak, a hardwood, and pine, a softwood, have in the past been the most common types of timber used in the UK. Prior to the Victorian Empire, they were the main timbers grown in UK woodlands, and were mostly used for shipbuilding, construction and furniture.

Since the 14th Century, the UK has traded in timber and wood products with Scandinavia and the Baltic countries. Good quality European pine, traded under the name of redwood, and European spruce, sold as whitewood, is still bought from those countries. Whitewood currently accounts for about 50% of Latvia’s total export value and Latvian government statistics show that in 2017, 17% of the country’s total wood exports were to the UK alone.

Today, the UK also sources softwoods from Sweden, Finland, Poland, Austria and Germany, and temperate hardwoods from France, Denmark, Romania and the Czech Republic, among other places.

A line of defence

Home-grown oak played a part in the UK’s growing prosperity and world influence last millenium, as it had been used to build ships for the Royal Navy from the 13th Century. In World War I (WWI), the majority of UK pine was used either for lining trenches and other buildings on the European front, or for pit props in coal mines, to power the war effort.

After WWI, UK timber resources were critically low. As a result, the Forestry Commission was established in 1919 with the purpose of growing a sustainable resource of timber for the nation. Its remit was to provide timber in preparation for a second global conflict. However, trench warfare was obsolete by World War II, reducing the need to stockpile wood and enabling it to be used elsewhere. Hence, the role of the Forestry Commission changed to that of providing a commercial timber resource and it is now responsible for sustainable wood management, including for public use.

Sitka spruce, a softwood native to Canada, was the principal tree chosen for the UK market under the Forestry Commission’s remit because it grows quickly and in poor soil. However, it proved less than ideal for many applications, due to a highly knotty appearance and inferior quality to other softwoods. But its fast growth rate meant it was still useful and available, so for many years it was relegated to low-quality purposes, such as for pallets and fencing timbers. While still not regarded as a high-quality joinery softwood, from the late 20th Century onwards, advances in mechanical grading have enabled the variety to become a major source of basic house-building structural timber.

The Soviet Union affected the timber trade throughout a large part of the 20th Century. Between WWI and the end of the 1980s, Russia’s annexation of the Baltic states Latvia, Lithuania and Estonia, meant the UK supply chain was filtered through Russian outlets until Latvia and the Baltics gained independence in 1991. During that time, other countries, including Sweden, Finland and Germany, filled the space and became major suppliers of construction and joinery softwoods to the UK.

Building and manufacturing

The favoured sources of timber for construction and manufacuring have changed over the centuries.

When explorers in the Victorian Era travelled abroad, Britain had started importing woods such as mahogany from South America, and other varieties from Ghana, Nigeria and Malaya - now known as Malaysia. When under Colonial rule, rules were put in place to ensure timbers in these regions were harvested sustainably.

From the Victorian Era to the 1970s, pine was used for flooring, joinery and beams in buildings, which has largely been replaced with pine for joinery, while building timbers are either European whitewood or UK-grown spruce. Domestic sources included elm, beech, ash and oak. Oak, the most popular hardwood, has always been used for furniture, joinery, flooring and beams. In the UK it is approximately 80% imported and 20% homegrown. Elm had been an especially popular variety for furniture before Dutch elm disease destroyed all of the trees during the 1970s.

As can be seen, much of the swapping and changing between markets has been out of circumstances beyond the UK’s control.

The fight for Notre-Dame

France is facing its own troubles with timber supply – in this case, repairing an 850-year-old building with an ancient wooden foundation.

During a €6mln restoration project, the Notre-Dame fire broke out in the attic of the cathedral on
15 April, days before Easter. The fire spread from the attic, which contained a lattice of wood beams, across the roof where it ignited and brought down the building’s iconic spire – a 750 tonne timber structure covered in lead.

The church’s history dates back to the 12th Century, when Maurice de Sully was the Bishop of Paris, from 1160-1196. Upon his election, he proposed building a cathedral dedicated to the Virgin Mary, Notre-Dame – our Lady, in French. The first stone was laid in 1163 in the presence of Pope Alexander III.

Notre-Dame is 130m-long, 48m-wide and 35m-high. The cathedral has a choir and apse, a transept, and a nave flanked by two aisles and square chapels. The Gothic towers at the western façade rise up 68m-tall. At the cathedral’s east end, the apse has large clerestory windows, added in 1235–1270, and is supported by single-arch flying buttresses. The cathedral’s three rose windows still have their original 13th Century glass.

Although stonework prevented further destruction and retained the majority of the cathedral, repairing the timber skeleton will be tough. Preservation group Fondation du Patrimoine Vice President, Bertrand de Feydeau, said the cathedral’s roof cannot be rebuilt precisely as it was because France does not have those same trees. The original timber came from very tall, mature trees cut in the 12th and 13th Centuries, and there are none remaining. As the funding donations roll in, action is already underway on sourcing the best replacement timber for the job.

French oak trees were used for the church’s structure. The ceiling is nicknamed ‘the forest’ because each of the estimated 1,300 beams came from a different tree. The frame measures more than 100m in length, 13m in width in the nave, 40m in the transept – the area that crosses the main body of the building – and 10m in height.

The scarcity of large timber, due to deforestation and urban development, made it necessary to use lighter-section timber that allowed the elevation of the frames and the increase of their slope. The oldest timbers, particularly in the choir section of the building, are thought to date back to the 8th Century. But finding forests of 400-year-old oak trees will be a near impossible task.

Columbia University Art Historian, Stephen Murray, told Ars Technica that the high-vaulted stone ceilings give the cathedral an open, cavernous feel and perfect acoustics for religious services, but they were also built to help protect the interior of the cathedral
from an event exactly like this one – the collapse of a burning roof.

‘The vaults are intended to fireproof the interior of the building,’ Murray said. ‘We don’t know yet, as far as I know, whether that has been effective. The weight of that steeple falling on top of the vault may have punctured the vaults.’

But Notre-Dame is no stranger to repair projects. The building has undergone several redevelopments in its time. Some of the changes in the 17th and 18th Centuries included replacement of stained glass and redevelopment of the Central Portal. The great organ was restored in the early 1990s.

Lead roofing consisting of 1,326 tables of 5mm-thick and weighing 210 tonnes sat on the frame. The material was chosen over clay as Paris did not have an abundance at the time.

The structures of the choir and the nave have lasted centuries, while the transepts on the northern and southern parts of the building, and the spire, were redone in the mid-19th Century.

The spire

The last incarnation of the spire – the tallest point of the building – was designed by Eugène Emmanuel Viollet-le-Duc, who was one of two architects commissioned to restore the cathedral. His spire replaced a previous one that had been removed in the 18th Century after exposure to high winds risked it collapsing.

The 92m Gothic-inspired design is made of wood and has a protective lead coating. At the base were statues of the 12 apostles and the four evangelists.

Finally, the rooster that sat at the top of the arrow contains three relics – a parcel of the Holy Crown of thorns, a relic of St Denis and one of St Genevieve. It was considered a veritable ‘spiritual lightning rod’ protecting all those who work for the praise of God, inside the cathedral.

Notre-Dame has powerful connections for society – French people are proud of the monument, and millions of visitors flock to the location, drawn by the deep history, architectural prowess, and literary poingnace.

As such the event has prompted passionate responses from supporters keen to see the catherdral restored to its former glory, as close to the original as possible. A national donation programme has been established to help restore Notre Dame, and French President Emmanuel Macron is aiming for a rebuild within five years.

Keep reading Materials World to find out more as the project unfolds.