Twyford Abbey was built on the site of an existing Manor House in the early 19th century as a ‘romantic castellated abbey’ in the Pimlico style. This included many Victorian gothic features to the facades, roofs and roof drainage systems which were very vulnerable to blockage and overcharging, and therefore required regular maintenance. The building was occupied as an Abbey and convalescent home throughout the 20th century, but reduced maintenance and heavy occupancy by feral pigeons resulted in defective roof drainage allowing chronic water penetration into the structures beneath.
This provided the conditions for dry rot (Serpula lacrymans) infection and decay to the structural softwood timbers built in contact with the masonry of the walls where these were subject to chronic water penetration from defective roof drainage. Dry rot is a ‘geophilic’ fungus in the wild which infects timbers built in contact with masonry subject to chronic water penetration from defective roof drainage. It is therefore often found extending in a ‘cone shape’ down through a building from a valley or parapet gutter or roof drain. Dry rot may persist in damp masonry for many years and decades; especially at and below ground level where the base of the walls and foundations will remain damp.
Dry rot will recur and spread in areas subject to further water penetration from roof drainage, plumbing leaks, and other sources of rising or penetrating damp. Dry rot may also spread through unventilated building voids and beneath impermeable surfaces under damp conditions. It was therefore often found spreading beneath ‘linoleum’ and other impermeable floor surfaces and behind lath and plaster in unoccupied, unheated buildings. This results in structurally significant decay and loss of original materials.
In the wild dry rot prefers to grow in materials with relatively high calcium and iron content, and like many decay organisms prefers added nitrogen in order to grow. It therefore grows well in masonry subject to chronic water penetration resulting in corrosion to ferrous fixings; especially when buildings are heavily occupied by feral pigeons. This is because feral pigeon faeces and nesting materials will result in blockage and overcharging of drainage systems, and allow water and nitrogen containing materials to penetrate through to structures beneath over many years. Dry rot is generally killed by ozone and other free radicals in fresh air and cannot grow in dry conditions. It is therefore generally controlled in occupied buildings with ventilation and heating, however dry rot will spread rapidly when ventilation and heating is restricted under reduced occupancy or unoccupied.
At Twyford Abbey, dry rot infection and decay had spread in many parts of the building subject to chronic water penetration from defective roof drainage and inadequate maintenance as described above. This had resulted in structural decay and failure to lintels over window and door openings, bearing ends of joists and primary beams, wall plates and bonding timbers built into the masonry. Dry rot had also spread to affect floorboarding and plaster. This was continuing to occur despite extensive previous remedial treatments and repairs. Generally, failure to prevent water penetration, the failure of previous chemical remedial treatments, and the introduction of impermeable materials on previous refurbishments was allowing the persistence of dry rot and further decay. H+R undertook detailed investigations to identify decayed, partially decayed and at risk timber elements by using H+R Rothound dry rot search dogs, and by deep drilling and probing. H+R also identified sources of water penetration and residual moisture in the structure by moisture profiling.
How we solved the problem:
H+R gave detailed recommendations for repair, conservation and remedial detailing so as to prevent further decay, so as to retain the maximum of historically important material, and so as to allow the eventual refurbishment of the building for future occupancy. This involved the isolation of vulnerable materials from damp, potentially damp or salt contaminated masonry, and the introduction of breathable materials and ventilation to building voids so as to allow long-term drying before, during and after refurbishment, and the eventual elimination of dry rot infection. No chemical remedial timber treatments or wall irrigations were required, and no injection of chemical damp-proof course materials or use of ‘proprietary tanking systems’ was required. This allowed significant budget and programme savings and the conservation of the maximum of historically important material as required by the planning and conservation authorities.