Care of Buildings

Current priorities

• Assessing moisture in building materials
• Controlling micro-organisms with UVC irradiation
• Ivy on walls
• 'Damp Towers': Reducing rain penetration in exposed masonry structures
• Design of cover buildings (shelters) for archaeological sites
• Environmental protective glazing
• Role of ventilation in conservation
• Soft wall capping as a conservation method for ruined monuments
• Conservation of fibrous plaster ceilings

Assessing moisture in building materials

Water is responsible for many forms of deterioration in a wide range of materials. Therefore, the ability to assess moisture conditions and understand moisture movement in materials is of considerable importance in the conservation of historic buildings. Excess moisture can accumulate in building fabric because of occupancy, building and services defects, or emergencies such as fire or flood. Whatever the cause, assessing the moisture conditions of building fabric can help in diagnosing faults, assessing risks of decay and deterioration, and monitoring drying after carrying out remedial works. In addition to the projects outlined here, further research into moisture movement is being carried out in connection with Energy Efficiency and Major Threats and Emergencies

Measuring moisture content in historic building materials

Most efforts to develop convenient moisture measuring and monitoring techniques for building materials have been developed for wood or concrete. In contrast, instruments for the accurate, convenient and non-destructive measurement of moisture in brick and stonework have proved particularly difficult to devise. The potential and limitations of a variety of methods for assessing moisture are currently being investigated in an ongoing programme of research. The aim of this particular project is to understand better the limitations of resistance moisture meters for assessing moisture content in timber, and the use of timber dowels for assessing moisture in porous masonry.

Participants: Ridout Associates

Read the Historic England research report: Measuring moisture content in historic building materials

Intercomparison of methods to assess moisture in porous masonry

Many different methods and devices are commonly used to assess damp problems in walls, but all have some drawbacks. There is a lack of agreement over how they should best be used, and little information over how they compare one with another. The first phase of this project aims to develop a common methodology for comparing the performance of different moisture measurement methods, starting with laboratory-based testing. The range of methods under review includes non-destructive resistance, capacitance and microwave moisture meters, along with other techniques such as TDR, IR thermography, timber dowels, and temperature and relative humidity probes. The second phase of research is investing the depth penetration provided by some of the more promising techniques identified in phase 1 on different materials (Portland limestone, new brick, old brick and lime mortar). Finally, the aim is to produce technical advice on best practice in the use of moisture meters.

Participants: University of Oxford; Historic Environment Scotland; Ridout Associates

Read more on Techniques for monitoring moisture in walls.

Read the paper from the 1st International Conference on Moisture in Buildings (June 2021) on: Assessing moisture in porous traditional building materials.

Development of a robust methodology for assessing moisture in solid brick walls

This project aims to investigate the uptake of moisture in masonry walls, and how this is affected by their existing moisture conditions. The project will concentrate on solid masonry walls built of brick and mortar.

A 4-year SEAHA doctoral programme commenced in 2017.

Participants: UCL; University of Oxford; Industrial partners.

Moisture movement beneath solid floors

Historic England is often called upon to give advice on measures to improve the energy performance of floors, or increase their resilience to flooding. Proposals often include the replacement of an existing floor with some form of insulated concrete or 'limecrete' ground bearing slab. It is a widely-held belief that if an impermeable ground bearing slab is installed in an old building, ground moisture will be 'driven' up adjacent walls. Although there are numerous references to this phenomenon, both in technical and product literature, they tend to be anecdotal and unsupported by scientific evidence. The objective of this project is to understand the influence of ground bearing floor slabs, both permeable and impermeable, on moisture movement within the walls of historic buildings. The project aims to answer the following research questions:

• How does the type of foundation slab material influence local ground moisture and water levels?
• How rapidly does liquid water and water vapour permeate through typical floor and wall materials?
• Does the choice of floor material influence soil moisture and the collection of water beneath building foundations?

The project comprises long-term field monitoring and laboratory-scale experiments to understand the physical processes and drivers. This will be supported by numerical modelling to project long term wall and slab moisture conditions for a range of building types, over long term changes in seasonal weather and a changing climate. The findings of the research will contribute to an evidence base that will enable informed decisions to be made about improving the energy performance and flood resilience of ground floor structures.

Participants: University of Bath

Read more about Water in permeable building materials - article in The Building Conservation Directory 2016, published by Cathedral Communications Ltd in 2016.

Read more about assessing moisture in building materials: Assessing moisture in porous building materials – article by Soki Rhee-Duverne in volume 164 of Context, the Journal of the Institute of Historic Building Conservation, published by Cathedral Communications Ltd in May 2020.

View the 2020 webinar: Survey and inspection: Damp
This webinar looks at the principles that should be adopted when investigating moisture-related issues in traditional buildings, including the factors to take into account when determining the causes of damp in old buildings. It also explains the potential and limitations of various methods for assessing moisture in building fabric and how measurement and monitoring can help in diagnosis of damp-related problems.

Read the paper from the 1st International Conference on Moisture in Buildings (June 2021): Towards a holistic view of moisture transport in historic buildings.

Control of micro-organisms with UVC irradiation

Micro-organisms can disfigure masonry surfaces and promote colonisation by higher plants. Traditionally, they have been treated by mechanical cleaning and the application of biocides, but these methods do not provide long-term protection. Therefore, more effective and persistent treatments are being sought. Trials with ultra-violet C (UVC) irradiation (a method widely used in industry to eradicate micro-organisms) have been encouraging, but the application of this treatment in conservation has still to be fully assessed.

Our current research project aims to establish and refine the parameters for applying UVC irradiation to porous inorganic surfaces affected by micro-organisms. The preliminary trials began at Newport Roman Villa (Isle of Wight) in 2008 on a Roman mosaic. These were very successful. Trials have been renewed at the Villa, and will subsequently be applied at a diversity of sites. Guidance on the application of UVC irradiation will be published from these controlled trials.

See latest research article on Control of Biological Growth on Masonry

Participants: Isle of Wight County Council; School of Biological Sciences, University of Portsmouth.

Ivy on walls

The aim of this project was to investigate whether ivy growing on masonry surfaces causes deterioration or acts protectively. The research questions addressed were:

• How does ivy alter the micro- and macro-climate at the surface of the stone and are the changes favourable?
• What are the physical and chemical effects of ivy roolets?
• Under what circumstances will ivy root into walls?
• Do ivy roots in the ground pose a problem?
• What is the best strategy for managing ivy on walls?

A programme of field investigation and laboratory experiments was carried out to answer these questions.

Participants: University of Oxford School of Geography and the Environment

The final report was published in April 2018:

• Ivy on Walls

Read more about this topic:

• Ivy on Walls: Seminar report (2010)

'Damp Towers': Reducing rain penetration in exposed masonry structures

This project began in 1989 in response to reports of church towers in southwest England where amounts of water ingress due to wind-driven rain had increased after repointing. Following site investigations, laboratory-based tests were carried out at Sheffield Hallam University to determine modes of rain penetration and liquid water movement in composite masonry walls. Site trials of rendering and grouting were then carried out. Both these treatments were found to be highly effective in reducing water ingress.  However, rendering has major impact on the appearance of the stonework, and grouting can be complex, time-consuming, and costly. Therefore, the current phase of the project is focussing on the pointing of joints. The aim is to see if pointing mortars can be developed that will be as effective as either rendering or grouting. Materials research and laboratory trials are underway at the University of Oxford to formulate and test a range of experimental mortars.

Participants: University of Oxford (Lucie Fusade); William Revie; Colin Burns

Read more about this project:
Damp Towers Conference, Exeter, 2013: Transcripts

Laycock, E and Wood, C (2014) Understanding and controlling the ingress of driven rain through exposed, solid wall masonry structures in Geological Society special publication; 391; pp175-191

Design of cover buildings (shelters) on archaeological sites

After excavation, archaeological remains are vulnerable to deterioration from dynamic environmental agents. Significant features, such as Roman mosaics, are often preserved and presented under cover buildings or shelters. There is a long tradition of this types of protection in England.

However, poorly designed cover buildings can harm the archaeological features they are intended to protect by creating environmental conditions that cause their deterioration to accelerate. This often stems from the designer’s lack of understanding of the condition and risk environment of the archaeological features.  

Historic England and its research partners are drawing on their extensive experience  to produce the first formal guidelines for the design and construction of cover buildings. A methodology for planning, designing and constructing such buildings has been devised to enable clients and architects to make informed decisions.

Participants: Historic England, The Getty Conservation Institute; Israel Antiquities Authority

Read more about this project:
Shelters for archaeological sites with mosaics - assessment

Read more about cover buildings:
Protective shelters for archaeological sites

Environmental protective glazing

Because stained-glass windows form part of the building envelope – separating the internal and external environments – they are uniquely vulnerable to aggressive environmental deterioration. On the exterior, rainfall, wind and pollution can cause structural and chemical deterioration of the glass and the leading; on the interior, condensation can cause irreversible loss of paint and other applied decoration. Unfortunately, our ability to improve the environmental conditions to which historic glass is subjected is limited. One of the few interventions available that can provide protection whilst keeping the historic glass 'in situ' is secondary glazing, in the form of Environmental Protective Glazing (EPG).

EPG has been used in one form or another since the 19th century, but while considerable design developments have taken place over that time, there have remained many lacunae in our understanding of how the system actually works. The confusion over technical aspects of EPG is highlighted by its popular name, 'isothermal glazing'.

Historic England's research shows the success of EPG actually depends on temperature differences. Historic England is regularly consulted about the merits and justifications of EPG systems for stained glass conservation. Since the remit of the organisation is to care for the historic environment as a whole, we do have concerns that, if the design of the EPG system is not approached with sufficient care and attention, the benefits to the glass can sometimes be at the expense of other historic elements, including the appearance of the window in its setting, and the exterior views of the building.

EPG is not a universal panacea: as ever with conservation, the undoubted gains must be balanced against the negative impacts. The decision about whether EPG is the right choice in a particular situation will depend not only on the nature and seriousness of the deterioration, but on the significance of the glass, the window, the building, and the setting.

Historic England's 43/2017 research report Conserving Stained Glass using Environmental Protective Glazing looks at whether EPG is robust enough to allow flexibility in design choices that could minimise harm. In other words, how might modifications of the basic design of EPG affect its effectiveness?

Historic England's 37/2023 research report Conserving Stained Glass Windows Using Tracery and Partial Environmental Protective Glazing looked at comparing performance of full EPG with partial and tracery EPG. This research demonstrates that, although there were some minor performance variations, in general the tracery and partial EPG performed in a similar way to full EPG, improving thermal buffering and significantly reducing the risk of condensation on the historic glass surfaces.

View the 2020 webinar on Conserving stained glass environmental protective glazing.
Stained glass windows are one of the most beautiful and significant components of historic buildings, but they also serve a very practical role in keeping out the weather, which makes them vulnerable to decay from wind, rain and condensation. This webinar looked at ways of dealing with environmental deterioration of stained glass, and reported on the findings of recent Historic England research into the benefits of environmental protective glazing.

Participants: Tobit Curteis Associates; Canterbury Cathedral Stained Glass Studios; Element Energy; Corpus Vitrearum Medii Aevi; LBW-Bioconsult.

Read more about this project:

• Protective glazing
• Dealing with environmental deterioration of stained glass.

Role of ventilation in conservation

This project investigates the role of natural ventilation in protecting timber from decay. Among building conservation professionals the accepted wisdom is that even a little air movement is better than none. However, there is little scientific evidence to support this view, and research carried out in Dundee found that small air movements stimulated rather than inhibited the growth of dry rot. The current project addresses the questions: Can air be made to flow in small cavities, and what would small air movements to achieve?  

Participants: Brian Ridout Associates; University of Manchester

Programme and progress:  First phase complete; Ventilation and Conservation report published.

Soft cappings to protect ruined masonry walls

'Soft capping' is a technique of using soil and vegetation to protect exposed wall tops. Ruined walls that have remained untouched for decades slowly build up a natural 'soft' cap.  When these have been removed during past consolidation works, little, if any, deterioration of masonry has been observed below this type of covering. Research carried out by Historic England (formerly English Heritage) has shown that soft capping protects the covered masonry from deterioration by freeze/thaw weathering. Soft capping also reduces potential damage to wall heads from the thermal movements. In addition, soft cappings also retains moisture during rain and reduces the amount of water running down the face of walls. This helps mitigate the cycles of wetting and drying might harm masonry surfaces.

Partners: University of Oxford School of Geography and the Environment; Colin Burns.

Read more about this project:
Soft Capping on Ruined Masonry Walls, Historic England Research Report number 88/2018, Chris Wood and Alan Cathersides (Historic England) and Heather Viles (University of Oxford)

Contact for all above projects: [email protected]

Conservation of fibrous plaster ceilings

Fibrous plaster was introduced into the UK in middle of C19th. It consists of prefabricated cast gypsum plaster elements, reinforced with hessian scrim and timber lath, hung from timber supports by wads of hessian covered with plaster. Fibrous plaster often incorporated elaborate mouldings and decorative enrichments. It became ubiquitous in commercial and cultural buildings, particularly in the form of suspended ceilings, until the first quarter of the 20th century.

Countless ceilings survive, sometimes undifferentiated from conventional lath and plaster. They are often complex in design, and the sudden partial collapse at the Apollo Theatre, London, in 2013 revealed the limitations in our understanding of these ceilings.

Historic England is undertaking research into the construction, deterioration, assessment, and conservation of fibrous plaster ceilings. The aim is to produce guidance on their care and maintenance. The project encompasses: historical research; survey and characterisation of surviving ceilings; new methods of non-destructive testing; materials testing.

Participants: Historic England's Building Conservation and Research Team; The Theatres Trust. In addition, future participants are likely to include commercial conservation contractors, industry representatives and academic institutions.

Read more about: Inspection and maintenance of fibrous plaster ceilings and the ABTT's guidance.