Surveys of historic and period buildings and methods of repair and care
As a company we have a special interest in period and listed historic buildings and are members of SPAB, (Society for the Protection of Ancient Buildings). The founder of SPAB, William Morris set about solving the issues of the nineteenth century by extending protection to buildings of ‘all times and styles’. At the core of this philosophy was the concepts of repair, care and sustainability.
In particular we adhere to the solution of damp problems in buildings which are period or historic in construction; by the use of sympathetic and traditional materials, such as lime-based renders and plasters.
The use of differing damp-proofing methods is analysed briefly below:
A Physical damp proof course can be inserted by cutting in or during rebuilding. Can cure rising damp but this drastic method is usually inappropriate.
Drawbacks: possible major structural problems; potential damage to historic finishes internally; unsuitable for randomly coursed walls; access difficulties; deterioration sometimes of masonry below damp proof course where moisture is concentrated.
Chemical: Walls impregnated with chemical solution through holes at bottom to create waterproof barrier are widely used today but not always appropriate for old buildings.
Drawbacks: drilling holes inadvisable in flint, granite, etc; hard to form proper barrier in rubble walls with voids; holes unsightly; deterioration sometimes of masonry below damp proof course where moisture is concentrated.
Cost: typically £195/m (including re-plastering). Ceramic tubes: Holes drilled to receive porous siphons approximately 50mm in diameter that absorb damp and evaporate it from each tube. Sound in theory but problems may occur in practice.
Drawbacks: salt accumulation in tubes may increase moisture; airflow sometimes inadequate; tubes commonly set in hard cement mortar; unsightly.
Cost: typically £125/m.
Electrical potential aimed at reducing capillary rise using electrodes bedded in wall. l Cheap but dearth of evidence that electroosmosis is effective and system rarely used today.
Drawbacks: adjustment of current needed to match variations in damp along a wall usually impractical.
An Austrian product presently under trial in the UK claims to inhibit the passage of water up a wall inducing a local magnetic field. Achieved noninvasively with unit plugged into mains, typically in loft.
Likely cost: £3,000/unit (one unit covers an average sized house).
However, in old buildings, walls were built thick enough so as damp would not penetrate to the inside. The joints were always lime mortars or earth. The joints were more porous than the building elements of brick or stone so as the joints would drain and shed water by evaporation, therefore not allowing damage to the masonry. The joints were the sacrificial element of the building. Because lime and earth mortars are so porous, timber in contact with lime mortar is less prone to decay than when bedded in cement mortar. Historic houses did breathe and shed water when built. They were also heated by coal or log fires in an open fireplace which promoted rapid air changes, through air being drawn out through the chimney. Windows and doors were not sealed as they are today allowing air movement into the building. Internal finishes were lime wash which allowed surfaces to breathe, and although it would discolour when damp, it would not peal from the wall like wall paper or blister like modern paint.
From the day they were built many of these buildings (not all) have had water from the ground, rising into the walls through capillary action. Water from the ground contains salts. Initially for many years the moisture in the walls would evaporate off harmlessly outside during fine dry weather, and inside, as a result of the rapid air changes induced by the open fire heating drawing air rapidly up the chimney.
When water from the ground evaporates the soluble salt it contains is left in the walls at the point from which it evaporated which would be in the surface of the masonry or in plaster finishes. Salts block the pores and cause damp to rise further up the walls to evaporate. A proportion of Salts are also hydroscopic and in humid conditions (Modern living no open fire) will attract moisture to the wall causing a damp area, or band even when there is no capillary moisture.
Rendering and painting reduce evaporation significantly from the outside surface of the wall, and cause damp to rise further up the wall and to appear on the inside. Renders crack and allow water to penetrate through, either by capillary action into fine cracks or directly as penetration into larger cracks and de bonded areas. The water is then trapped behind the render and can penetrate to the inside. All of the above means that by the 21st century a great many old traditionally built houses have damp problems often caused over the last 100 years, by changes in heating and finishes, these damp problems have not been addressed due to a lack of knowledge and understanding of older buildings, traditional materials and the way they work together.
The Survey The biggest problem for older properties is the method of surveying. Most surveys on old properties are commissioned by Estate Agents or lenders when they are sold. Most estate agents have only one interest that is selling the house at the best price. The Royal Institute of Chartered surveyors, Trading Standards, and even The Estate agents’ professional bodies, all state that surveys should be carried out by a qualified Chartered surveyor, and any work should be carried out by a BWPDA member company. This is often in the terms of the mortgage company instruction. However, most Estate agents will try and use a cheaper unqualified company for a free survey. It is these companies, who, through a lack of training and understanding will usually in an effort to provide the cheapest quickest fix, will recommend the installation of a chemical Damp Proof Course and often precautionary timber treatments.
Given that the survey is free there is some pressure to find some work. It costs on average £150+vat to attend a property write a report and send it. These costs have to be recovered somewhere. In the ideal world surveys would be commissioned by Building Surveyors or Architects who would undoubtedly use a surveyor or company that they knew to have the relevant experience knowledge and qualifications. If Solicitors had a better understanding of guarantees they would insist that work was carried out by qualified companies, and that guarantees issued were meaningful and enforceable, and also underwritten by insurance and not by chemical companies for the protection of their clients, this would ensure that companies did not use chemicals where they were not necessary, just to comply with the terms of the guarantee.
The walls can still become damp with the application of lime plasters after a short period of time of the building work completed if incorrectly specified. The lime mortar has had to be removed and replaced with a Ventilated Plaster lathe. In times gone by, houses were lined with timber wainscoting (a stud work on the wall with vertical boarding over) when they became damp. Grander houses had internal stud work and lathe linings or Hessian stretched over timber and then papered.