The roof of West Horsley Place has weathered many winters, and is in great need of comprehensive conservation and repair. Today it exhibits the symptoms of age common to many historic buildings of its type, as old materials deteriorate through exposure to the elements. The roof is constructed of clay plain tiles laid on timber batten, a practical construction for excluding water from the interior. The fired tiles themselves are hard and brittle, and when laid in alternating rows they form an effective barrier against wind, rain and snow. They are hung on the underlying timber with iron nails or wooden pegs, and many of the latter still in situ are centuries old. Battens are nailed laterally across the roof rafters and the internal timber structure of the roof, though designed to be pleasing to the eye, is an impressive feat of engineering calculated to support the weight of the thousands of tiles above it.

Much of the roof lacks any internal water-resistant membrane that we might expect in the attics of modern homes, however in some areas late 20th century bitumen felt can be found, potentially part of a repair commissioned by Mary, Duchess of Roxburghe. Generally the roof is ‘left open’ with air able to pass beneath the tiles to circulate around the attic space. This is beneficial for the historic timber inside, as this circulation reduces the potential for lingering moisture and the accompanying effects of mould and pests. Despite this, years of deterioration and leaks have resulted in numerous forms of damage to the roof.

This year we have carried out a package of urgent works to the roof to stabilise the most concerning areas of weakness and rainwater ingress and limit future deterioration in these areas before a future, thorough roof conservation project.

The roof of the manor house supports thousands of tiles, and whilst these are made of tough, fired clay, the combined effects of frost and plant growth has inevitably caused many to become ineffective. Delamination, cracking or spalling occurs gradually but relentlessly, resulting in some tiles that are beginning to break down, and some that have crumbled away completely. The growth of moss on the tiles has a highly negative impact on the roof’s effectiveness. Moss traps moisture against the tile’s surface, and this is particularly troublesome during the winter where freezing and thawing causes repeated expansion and contraction. For tiles to remain most effective, they must be clean and clear of plant matter and debris. We have been clearing moss and other plant life from the roof wherever we can, helping us to get greater longevity from our tiles.

Some tiles have been replaced altogether with tiles that are suitably patinated and cohesive with the appearance of the roof. Replacement has occurred on the roof’s pitched surface, in the valleys, on ridges and where bonnets are fitted to roof hips. In some of these areas clear holes have been filled, whereas some leaks were more difficult to locate. The experienced roofers on site were very successful in tracking leaks to their source. The moisture that has found its way into the roof has caused corrosion of the nails in some areas. When iron corrodes it increases in volume, and this has cracked numerous tiles (this is called ‘nail sickness’). These have also been replaced. Perhaps the most difficult part of the project was access to the areas that require repair. Replacement of the tiles can be fairly simple, with a new tile slotted into the row and hooked over the batten with integral lugs or nails. The height of the manor house and the steep pitch of its roof means that careful planning was needed to design the correct scaffolding arrangement, and manoeuvrable portable access towers and long ladders were also used.

Along the roof’s ridges and hips, tiles are bedded with mortar. This material, like the tiles themselves is hard-wearing and weather resistant however whilst it can be expected to last for many decades eventually leaks form underneath the tiles. We have re-bedded these tiles in several key areas, such as above the north end of the 1425 CE west range, and above dormer windows along the south elevation. The most challenging task was the repair of a large mortar fillet located behind the south elevation central gable, a section of roof that required excellent access planning and balance on a ladder to access. This gable was built as part of the façade development in the early to mid- 17th century, and since its construction there has been some movement away from the roof. A large gap of several inches had formed, and this was allowing rainwater into the walls where important structural timbers are located. Once the old, cracked mortar had been carefully removed, the gap was bridged with tiles to create a strong bed for the new fillet. This area was one of our greatest concerns, but now this work is complete the interior timbers and rooms below have been safeguarded for several years.

The roof of West Horsley Place was once covered with lead, along its box gutters and atop the decorative brick pilasters at the south elevation. We are working to return this to several areas where it is missing, and part of this package of works involved the installation of new leadwork at the tops of pilasters and surrounding dormer windows. These are areas over which water flows and settles, and if left unprotected the surrounding brickwork and timbers are vulnerable to water ingress.

There is much more to do to consolidate the roof of West Horsley Place, and what is described above represents a small portion of the work that has been carried out. In the future, we will need to carry out repairs on a much larger scale but what has already been achieved represents an important intermediary measure to repair the most vulnerable areas.