Principles of Repair for Historic Buildings
The objective of repair is to reduce the long-term deterioration of a building's fabric by remedying the cause of any defects. This in turn sustains the significance of the building, but to achieve this there needs to be sufficient information to understand the impact of the proposed repairs.
A conservative approach is fundamental to good conservation - so retaining as much of the significant historic fabric and keeping changes to a minimum are of key importance when carrying out repair work to historic buildings.
The unnecessary replacement of historic fabric, no matter how carefully the work is carried out, can in most situations have an adverse effect on character and significance.
The detailed design of repairs should be preceded by a survey of the building’s structure and an investigation of the nature and condition of its materials and the causes and processes of decay.
Repair can also help to reveal significance. An inappropriate alteration may have been made in the past, which is causing damage and looks unsightly.
Approaches to repair
- Only techniques and materials which have been demonstrated to be appropriate to the fabric should be considered. These will normally be the same as the original or parent material or where this is no longer available or appropriate, have compatible properties, both technically and aesthetically.
- Interventions should maximise the life expectancy of significant building fabric consistent with sustaining its significance
- Interventions should be reversible, if technically feasible and practicable, or at least, retreatable and should not prejudice future interventions when these become necessary.
- All works should be adequately recorded and the records made available for others
- Interventions should contribute to or at least not compromise the sustainability of future management and maintenance
To carry out effective repairs you need to understand how a building works and why its materials are starting to fail, as well as what can be done to prevent it happening again.
This requires a detailed examination of all the evidence which may involve selective testing and monitoring of the building’s condition over time.
Different types and periods of structure present different problems, so solutions must always be site-specific. Inappropriate or poorly-executed repairs may fail prematurely and accelerate the deterioration of the original building fabric, increasing the extent and cost of future maintenance and repairs.
While extensive investigations and monitoring may in theory be desirable, often the depth of such assessment is constrained by various factors. These include cost, difficulties in obtaining access or restrictions on opening-up building fabric or monitoring, and may be influenced by the requirements of funding bodies.
A two-stage approach can be helpful in deploying resources.
The first involves establishing an overview of the significance of the building and its general condition together with an initial idea for a programme, access issues and resourcing. This helps to define the scope of a second more detailed and often targeted stage of assessment.
Establishing a repair strategy requires a regular review of information to determine a particular course of action. If the information is inadequate further investigation may be required before any decision is made.
All of the practical options should be considered and the final choices should be those that either eliminate or more usually minimise harm to the significance of the building.
Devising a repair strategy
- Arrive at a comprehensive, soundly based diagnosis of deterioration and its causes
- Define the objectives of treatment or repair and any constraints
- Determine how urgent the need for work is
- Establish the likely extent of the works needed to meet the conservation objectives, including mitigating the causes of deterioration
- Assess the available resources (knowledge, skills, materials, finance)
- Identify options that meet the objectives for treatment or repair
- Assess the ‘buildability’, effectiveness, cost and maintenance implications of options
- Assess the impact of these options on the heritage values of the elements affected and thus on the significance of the building as whole
- Select options that minimise harm to significance, while being effective and affordable
- Determine priorities for implementation