Restoration in the built environment
Restoration is the process of returning a building to its former state. Historic England define this state as being ‘...a known earlier state, on the basis of compelling evidence, without conjecture.’
Restoration work is most commonly undertaken on historic buildings; accurately recreating its form, features and character as it appeared at a particular time, while protecting its heritage value. Decay or alterations made to the building can be reversed as part of restoration works.
Restoration aims to achieve a high level of authenticity, replicating materials and techniques as closely as possible. Where necessary, modern works, such as replacing outdated utilities, or installing climate controls, alarm systems, and so on, are undertaken in a concealed manner where they will not compromise historic character.
Criteria that might be used to assess whether restoration works are acceptable include:
- The effect of restoration work on the overall heritage value of the building.
- The weight of evidence for need for the work.
- Whether the work respects the previous forms of the building.
- The implications of the work in terms of ongoing maintenance requirements.
The basic principles that should be taken into consideration, particularly for structural restoration:
- Having sufficient respect for the original materials.
- Respecting the valid contributions of all periods on the building.
- Replacement of missing parts must integrate harmoniously with the whole.
- Additions should not detract from the building, its setting or relation with surroundings.
- Use of traditional techniques and materials.
- Modern techniques and materials are admissible where traditional alternatives are not feasible.
Restoration techniques can be classified as either reversible or irreversible. Reversible actions may be preferable as they can be subsequently replaced without damage to the original fabric, for example if further restoration is required, or if better techniques or materials are developed in the future. Typical examples of reversible techniques include:
- External buttresses.
- Ties at arch springings.
- Rings at the base of domes.
- Prestressed unbonded stitches.
- Anastylosis of stone or marble monuments with dry joints.
- External ties.
- Improvement of the strength, stiffness and ductility of existing diaphragms.
However, it may not be possible to use reversible methods for interventions, and some interventions cannot be easily undone without causing damage to the existing structure. Typical examples of irreversible techniques include:
- Groutings.
- Bonding-in of new bricks across cracks after grouting and cutting out to each side.
- Deep rejoints.
- Rebuilding of part of the facings of walls.
- Stitching of walls with prestressed rebars.
- Reinforcement of masonry with steel bars.
- Connection of marble or stone parts with bonded dowels.
- Skins of reinforced concrete on masonry.
- Strengthening of foundations.
The compatibility and durability of the replacement materials should be considered carefully. They should be compatible with the existing building in terms of chemical, mineralogical, physical and mechanical properties, as well as being aesthetically harmonious. Other points to consider are the strength, stiffness, bonding, thermal expansion, and permeability as well as problems such as efflorescence.
Common types of non-metallic materials for irreversible interventions are as follows:
- Stone and marble.
- Brick.
- Concrete.
- Mortar and grouts (Portland cement, lime-cement, pozzolanic, epoxy resin).
Where high tensile strength or prestressing forces are required, steel is often used, as well as fibre composite cables.
Paintwork and renderings can degrade due to air pollution, acid rain, UV radiation, and so on. Historic paint analysis of old paint layers can determine the original pigmentation and enable a chemical recipe to be reproduced. Often, modern substitutes have to be used, as some paints were originally manufactured using harmful materials such as arsenic and lead.
NB High Speed Rail (Crewe – Manchester) Environmental Statement, Glossary, abbreviations and references, published by the Department for Transport in 2022, defines restoration (ecology) as: The re-establishment of a damaged or degraded system or habitat to a level similar to its original condition.’
And restoration (ground) as: ‘The works delivered following completion of excavation, including regrading of excavations, the placement and preparation of soils, and landscape treatment.’
[edit] Related articles on Designing Buildings
- Anastylosis.
- Archaeology and construction.
- Building Preservation Notice.
- CIOB conservation scheme welcomes retrofit roles.
- Conservation of the historic environment.
- Curated decay.
- Flexbury Church.
- How to clean masonry.
- Interview with Kevin Borg, founder of KJB Building Consultants.
- Library of Celsus.
- Licence for Alterations for Apartment.
- Licence to alter.
- Listed buildings.
- Making good.
- Principles of conservation.
- Refurbishment.
- Remedial works.
- Renovation.
- Restoration v repair.
- Retrofit.
- Scheduled monuments.
- Types of brick arches.
IHBC NewsBlog
Mayor of London and Government announce bold plans to transform Oxford Street
Plans include turning the road into a traffic-free pedestrianised avenue, creating a beautiful public space.
Crystal Palace Subway, for 160th anniversary
The remarkable Grade II* listed Crystal Palace Subway in South London begins a new era following major restoration.
National Trust brings nature back to an area twice the size of Manchester in less than a decade
The National Trust has achieved its aim of creating or restoring 25,000 hectares of priority habitat on its land by 2025.
18th-century hospital in York to become sustainable homes
A former mental health establishment founded by a Quaker in 1792 is to be converted into 120 energy-efficient homes in York.
Context 180 Released - Where Heritage and Nature Meet
The issue includes life, death, Forests, bats, landscapes and much more.
Church architecture awards 2024: now open
The National Churches Trust has announced three awards, all of which are run in partnership with the Ecclesiastical Architects & Surveyors Association (EASA).
The essential sector guide includes officers' updates and a foreword by EH Chair Gerard Lemos.
Historic England opens nominations for the National Blue Plaque Scheme
The scheme is open to nominations to celebrate people from all walks of life.
Striking photos show nature reclaiming brutalist concrete
‘Brutalist Plants’ explores nature’s links to the architectural style characterised by imposing form and exposed concrete.
Purcell’s guidance on RAAC for Listed Buildings in England & Wales
The guidance specifically focuses on Reinforced Autoclaved Aerated Concrete (RAAC) in listed buildings.
Comments
[edit] To make a comment about this article, click 'Add a comment' above. Separate your comments from any existing comments by inserting a horizontal line