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 Where necessary, modern works, such as replacing outdated utilities, or installing climate controls, alarm systems, and so on, are undertaken in a concealed manner where they will not compromise historic character.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.
- 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:
- 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.
- Mortar and grouts (Portland cement, lime-cement, pozzolanic, epoxy resin).
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.
 Find out more
 Related articles on Designing Buildings Wiki
- Archaeology and construction.
- Building Preservation Notice.
- Conservation of the historic environment.
- How to clean masonry.
- Library of Celsus.
- Licence to alter.
- Listed buildings.
- Making good.
- Principles of conservation.
- Remedial works.
- Scheduled monuments.
The Construction Industry Council’s (CIC’s) ‘CIC Coronavirus Digest – Issue 8’ surveys the latest government advice with updates from the construction industry.
Organisations with conservation links have been collating resources on COVID-19 impacts, including Built Environment Forum Scotland (BEFS), Historic Environment Forum, The Heritage Alliance (THA), and Historic England, on cleaning surfaces.
Councils are reported to be considering taking up rarely-used executive powers to keep the planning and development system moving during the coronavirus pandemic.
Historic England's 'After a Flood' provides timely advice on how to dry walls properly and avoid further damage to the building fabric.
Context Issue 162 offers a peek into an archive of timber conservation history through the records of the practice of FWB and Mary Charles Chartered Architects.
To meet the government’s target of being carbon neutral by 2050, we must recycle, reuse and responsibly adapt our existing historic buildings, according to this year’s Heritage Counts report, so Historic England and partners are calling for a reduction in VAT rates to incentivise this more sustainable option.
Donald Insall Associates, with the help of Historic England, has completed restoration work of Moseley Road Baths, being converted for use as an arts and culture venue.
Celebrate your local ‘retired members’ and ‘successful learners’ with £500 cash prizes and 2020 Brighton School places!
The Conservation Hierarchy is a new framework developed by the University of Oxford to help construction projects achieve Biodiversity Net Gain.
Jacqueline Hughes, senior risk analyst at Equib, in pbctoday discusses how project managers for town centre developments can get their risk management strategies right.
A new paper from the Adam Smith Institute argues that the problem with the High Street has been totally misunderstood, saying that we need to reform restrictive planning rules and reject a policy of managed decline to reinvigorate our town centres.
The Whole Life Cost of Energy (WLCoE) calculator – issued by government in BETA form – is intended to help building owners and operators to understand the full financial cost of the energy their buildings use, and welcomes feedback.