Conservation

Buildings Conservation

From prehistoric monuments and Roman forts to medieval castles, Georgian country houses and Victorian palaces, English Heritage cares for over 400 historic buildings, each with their own unique conservation needs.

Our buildings are constantly monitored for damage and deterioration, with our experts carrying out vital conservation work and preventative care to ensure these historic sites can continue to be enjoyed for many years to come.

Learn more about some of the techniques we use to care for our buildings, and explore some of the unique projects we’ve carried out in recent years.

Conservation stories

Find out more about some of our most recent conservation projects to protect our buildings. 

A stone being removed during the conservation of Lincoln Medieval Bishops’ Palace, where a plant root had found its way into the structure of the wall
A stone being removed during the conservation of Lincoln Medieval Bishops’ Palace, where a plant root had found its way into the structure of the wall

Threats to Buildings

Stone and bricks are known to be very strong building materials and are used across most historic buildings. However, without special care there is a risk that these materials could deteriorate over time.

One of the biggest challenges in caring for these sites is damage caused by rain water. As well as contributing to erosion decay, if water penetrates the joints or any cracks in walls it can weaken and wash out mortar, increasing the risk of structural failures. And in the winter months, trapped water can freeze and fracture stone. Historic interiors and collections are also at risk of damage if water enters a building.

Plant growth on buildings also causes huge problems. Some plant life can spread from the ground and take root in stonework. The more harmful varieties establish deep roots which harden and broaden over time. If plant growth is not kept in check, their roots can creep into the joints and gaps between the stones, wearing and dislodging material, and allowing water to enter the core of the wall.

The threats of moisture and plants on buildings are becoming larger issues as climate change brings more rainfall, rising sea levels, frequent storms, and wetter winters that promote increased plant growth.

A specialist conservator scales the walls at Dover Castle to clean plant growth from the stonework. The varying size, condition and location of our sites means that some conservation work can be incredibly difficult to carry out
A specialist conservator scales the walls at Dover Castle to clean plant growth from the stonework. The varying size, condition and location of our sites means that some conservation work can be incredibly difficult to carry out

Combating the issues

Our teams carry out regular maintenance to our buildings in order to prevent serious damage before it occurs. This includes removing harmful plants and protecting exposed masonry where appropriate. Soft-capping is also a commonly used technique for protecting the tops of walls, particularly on exposed ruins. It involves placing turf on the top of the wall to absorb excess moisture and insulate it from frost.

Even with regular maintenance and preventative measures, sometimes damage and deterioration can occur to stonework, which will require repair. Repointing is the most common repair we will make. This is where we fill any open joints in the face of a wall. Loose or dislodged stones are re-bedded in their original positions. We always try to use mortars which reflect the character and performance of those used historically. Generally this means using lime mortars, which are weaker than modern cements but more porous, allowing the stonework to breath and helping to release any moisture that might have entered the wall.

Cracked stones can often be repaired by pinning and grouting. But sometimes the original stones are damaged beyond repair and we will carry out careful research to source the best matching stone material. Stonemasons will cut the stone to shape and tool the visible faces of the new stone to ensure that the texture matches that of the original.

In some rarer cases, greater interventions are required, for example inserting steel pins into weak points within a structure to provide long term stability. We always aim to conceal these measures with stone and mortar to preserve the historic character of the building.

Roof repairs were carried out at Audley End House and Gardens, Essex in 2017 as part of a major conservation project at the estate
Roof repairs were carried out at Audley End House and Gardens, Essex in 2017 as part of a major conservation project at the estate

Upkeep at Country Houses and Halls

Much like our own homes, historic houses require regular maintenance in order to restore any damage caused from general wear and tear and to protect the building for years to come.

Some challenges that conservators face with the upkeep of our historic estates include:

  • Water damage, often caused by damaged roofs or poor drainage on the outside of the building, which can promote mould growth and poor air quality.
  • Light damage, which can deteriorate collections within the building and degrade paintwork on the exterior.
  • Old infrastructure such as poor wiring or heating, which is both energy-inefficient and can become dangerous if left unaddressed.

Necessary interventions might include refreshing exterior paintwork, repairs to the roof, timber repairs to windows, rewiring, and improving drainage. Any repairs have to be carefully considered to ensure the integrity and history of the building is maintained while also creating a safe environment for any collections that may be on display inside, and for visitors and staff.

Millwright Tim Whiting during the restoration of Saxstead Green Post Mill
Millwright Tim Whiting during the restoration of Saxstead Green Post Mill

Unique Structures

The diversity of our sites means we often need to undertake more unusual projects that are completely unique to a specific building. In 2018–19 we carried out major conservation work on Saxtead Green Post Mill in Suffolk, including replacing the internal stairs and the construction of completely new windmill sails. This work had to be carried out by a specialist millwright and required extreme precision to protect the structural integrity of the building, and to ensure the mill could function perfectly.

Another example of a unique project is the maintenance of the thatched roof of the reredorter at Mulchelney Abbey, in Somerset. The reredorter is a 13th century toilet building used by monks – one of the best preserved examples in Britain. After damage caused by storms, the roof needed to be replaced in 2020–21. Historically, the thatch material used for Mulcheney’s roof would have been a by-product of the harvest of cereal crops. However, today the straw from modern crops is too short for thatching use and so specially grown thatching straw had to be sourced for the project. 

The mahogany staircase at Marble Hill
The mahogany staircase at Marble Hill

Even Stonehenge, which has survived for thousands of years, has seen the effect of weathering over time. When conserving Stonehenge our team use specialist hand tools to carefully clear out any loose or eroded mortar from the gaps between the stones, and then replace the modern cement (used by conservators in the 1960s) with traditional and breathable lime mortar. While carrying out this work, we are very careful to protect the many different types of lichens that grow on the stones. They’re an important part of the ecosystem, and a vital part of the character of the stones themselves.

Sometimes internal features of a building require specialist attention, for example, the mahogany staircase at Marble Hill House, London, which was examined and repaired as part of a major conservation programme at the estate in 2019–21. Over time, the stair treads (the top of a step) had moved under the weight of people climbing them, meaning that they were not entirely level, and there was concern that this might worsen over time. Investigative works were undertaken by a team of specialists including a conservation architect and carpenter and it was found that at some point a supporting timber beam had been partially cut away to allow additional headspace to the passage beneath the stairs. This had weakened the structure causing the deflection to the treads. The beam was extended and supported to ensure that the staircase remains structurally sound

Read more about the conservation of Marble Hill

New Technology

We use a range of non-destructive technologies to monitor moisture content and other conditions in the walls of our buildings. With the help of Historic England, we can use techniques such as X-ray fluorescence spectroscopy (XRF), infrared thermal imaging and measuring microwave responses to tell us more about salt levels, microbial growth and the presence of trapped moisture in walls. The simplest and quickest of these is thermal imaging. Wet materials lose heat more readily so wetter parts of a structure will show up as being colder on the imaging.

Other new technologies such as laser scanning and 3D imaging can help us to record more information about a building and allow us to survey and monitor it for any signs of deterioration in the future. At Lincoln Medieval Bishops’ Palace we used laser scanners combined with photogrammetry to build up an accurate 3-dimensional image of the ruins. This imagery and data provides us with precise measurements of the site as it is now, and will allow us to monitor the tiniest changes over long periods of time.

Explore the 3D models of the Alnwick Tower and the kitchen and chapel areas at Lincoln Medieval Bishops’ Palace below.