‘Greening’ the conservation of ruined heritage sites using soft capping and ivy
Submitting InstitutionUniversity of Oxford
Unit of AssessmentGeography, Environmental Studies and Archaeology
Summary Impact TypeEnvironmental
Research Subject Area(s)
Built Environment and Design: Architecture
Summary of the impact
The impact of this research has been to change architectural conservation
practice to utilize plants as agents of conservation rather than remove
them from ruins and other heritage sites. The impact stems from new
scientific evidence based on integrated laboratory and field studies
carried out at the School of Geography and the Environment in Oxford, by
Professor Viles and her team, demonstrating that plants and other organic
growths can be protective and contribute to successful and cost-effective
conservation of heritage sites. The impact has been realised through close
collaboration with English Heritage throughout the research process.
From the mid-1990s, novel research at the margins of geomorphology and
ecology carried out by Heather Viles and colleagues in Oxford has
evaluated the bioprotective and biodeteriorative roles of different
species and communities through empirical studies (linking laboratory
experiments and field trials) and the development of theoretical models.
This interdisciplinary research indicates that biodeteriorative impacts
are often minor (and have been over-stated in the past), whereas
bioprotective effects can be pervasive and strong (and have been
under-estimated in the past) [Section 3: R1]. In architectural
conservation practice however, plants are usually seen as causing
deterioration and removed, in ignorance of this scientific evidence. Ruins
pose a considerable challenge for conservation, as the loss of roofs
removes protection to walls, encourages colonization by plants, and
accelerates deterioration. There are at least a thousand ruined sites in
the UK, as well as many thousands worldwide, and thus decisions about best
conservation practice for ruins will have wide-ranging impact.
a) Soft capping research project: As a result of an invited talk
on this research at a Heritage Conservation Seminar hosted by the
Department of Archaeology, University of York in the late 1990s, Prof
Viles was asked to bid for English Heritage funding for a pilot study to
develop a methodology to evaluate the impacts of soft capping on the top
of ruined walls. Soft capping consists of a thin layer of soil (5 - 10 cm)
planted with drought-tolerant vegetation (e.g. grass or sedum plants).
Soft capping grows naturally on ruined wall heads and English Heritage
were keen to scientifically assess whether it had any protective role, as
initial trials at some of their ruined sites had proved encouraging. The
results of this pilot study were published in an English Heritage Research
Transactions volume [R2] and led to an ongoing, eight-year
research project (funded by English Heritage and led by Viles (Oxford) and
Wood (English Heritage)). The project has developed an innovative,
integrated programme of laboratory and field experiments on test walls and
on-site testing across England to provide a broad evaluation of the
efficacy of soft capping. The research has provided extensive empirical
demonstration that soft capping reduces the thermal fluctuations at wall
heads, minimising the risk of frost damage [R3]. Also, the
research has demonstrated that soft capping can have a regulating effect
on moisture regimes towards the top of ruined walls, reducing water
penetration into the walls and runoff down the external face [R4].
So far, the research has found no evidence of accelerated deterioration
under soft capping. A range of different types of soft capping have been
evaluated, including grass and sedums.
b) Ivy on walls research project: As a result of the developing
collaboration with English Heritage on soft wall capping, a further
research project was designed in discussion with them to evaluate the role
of ivy on historic walls, as ivy is both commonly found at many ruined
sites and blamed for much deterioration. This has become a seven-year
research project (also funded by English Heritage), which involves a novel
programme of laboratory analyses, detailed investigations on test walls,
and on-site monitoring across England. The major research findings, so
far, are that ivy provides an effective thermal blanket for wall faces and
also prevents particulate pollutants reaching the wall [R5, R6].
Also, no significant deteriorative impacts of ivy's aerial rootlets have
been found, and on- going research at our test wall site is providing
unprecedented scientific evidence for when, and why, ivy roots grow into
walls, and what the impacts are.
These English Heritage-funded research projects have materially
benefitted from, and, in turn, influenced, a number of other research
projects by Heather Viles and colleagues, which have developed novel
non-destructive test methods for investigating moisture in walls
(Leverhulme- funded) and looked at algal greening of walls (EPSRC-funded).
The research has been led by Heather Viles, starting with her arrival in
the School of Geography and the Environment, University of Oxford, in
1996. The key researchers included a number of DPhil students, research
technicians and post-doctoral researchers within her group: Dr Larissa
Naylor (DPhil student, 1998-2001), Dr Nick Carter (DPhil student,
1998-2002), Dr Troy Sternberg (PDRA, 2007-2009), Dr Julie Eklund (PDRA,
2008-2011), Zoe Lee (research technician, 2008-9), Hong Zhang (Research
technician, 2008- present), Dr Martin Coombes (PDRA 2012-present).
References to the research
Supporting grants: English Heritage soft wall capping (£219k) and ivy on
walls (£195k) - both non- FEC; EPSRC climate change and greening of walls
(£800k), the Leverhulme Trust climate change and moisture regimes (£164k).
References: (All of the following are international peer-reviewed
outputs, except R2 which was published in English Heritage's `gold
standard' publication vehicle)
R1: Carter, N.E.A. and Viles, H.A. (2003) Experimental
investigations into the interactions between moisture, rock surface
temperatures and an epilithic lichen cover in the bioprotection of
limestone. Building and Environment, 38: 1225-1234.
(Illustrates the development of multi-method experimental techniques to
evaluate the role of organisms on building surfaces)
R2: Viles, H.A., Groves, C. and Wood, C. (2002) Soft wall capping
experiments. In, John Fidler (ed.) English Heritage Research Transactions,
Stone, 2: 59-73.
(Presents the results of the pilot study experiments, and provides a novel
experimental approach to evaluating the pros and cons of soft capping).
R3: Viles, H.A. and Wood, C. (2007) Green walls? Integrated
laboratory and field testing of the effectiveness of soft wall capping in
conserving ruins. In, Prikryl, R. and Smith, B.J. (eds.) Building stone
decay: from diagnosis to conservation. Geological Society Special
Publication, 271: 309-322.
(First presentation of our integrated field and laboratory testing
R4: Sass, O. and Viles, H.A. (2006) How wet are these walls?
Testing a novel technique for measuring moisture in ruined walls. Journal
of Cultural Heritage, 7: 257-263.
(Provides proof of utility of 2D resistivity surveys to monitor moisture
under soft capping on historic walls)
R5: Sternberg, T., Viles, H.A., Cathersides, A. (2011) Evaluating
the role of ivy (Hedera helix) In moderating wall surface microclimates
and contributing to the bioprotection of historic buildings. Building and
Environment 46(2): 293-297.
(First report of thermal blanketing role of ivy, based on England-wide
R6: Sternberg. T., Viles H.A., Cathersides, A. and Edwards, M.
(2010) Dust particulate absorption by ivy (Hedera helix L) on historic
walls in urban environments. Science of the Total Environment, 409(1):
(First report of the role of ivy in absorbing dust and how this protects
Details of the impact
The impact of this research has been twofold: (a) changed conservation
practice to incorporate plants in architectural conservation; and (b)
enhanced information for conservators about the roles of plants in the
conservation of ruins.
(a) Changing conservation practice to include plants in architectural
conservation has been influenced directly and indirectly by the
research [R2]. English Heritage has begun to adopt soft capping,
and has advised many other organisations on the use of the technique [Section
5, C1]. For example, the results of the first phase of field trials
at Hailes Abbey (where we monitored changing moisture levels in walls with
and without soft capping [R4]) were used by English Heritage south
west region as evidence of the success of soft capping, after which larger
areas of the ruin were soft capped as a preventive conservation strategy.
Subsequently, and uniquely in the UK, the whole site was soft capped in
early 2013. This project cost £50,000 and has received much attention and
discussion [C2]. Further afield, the Institut du Patrimoine Wallon
sought advice on how to soft cap 11th century ruined walls of the abbey
church at Stavelot, Belgium, given its hostile climatic conditions [C3].
Building on the results of the research, the work went ahead in November
2011. The managers of other sites have also subsequently expressed
interest (e.g. Chaco Canyon, New Mexico). Similarly, the soft capping
research [R2, R3, R4] forms the major scientific evidence for the
performance of soft capping in the two-volume report commissioned by
Historic Scotland, launched at a seminar on 15th September 2011, and
underpins their trials of the technique in Scotland [C4].
Indirectly, the research on ivy has been very influential having received
considerable media coverage, provoking many requests for advice from
independent building owners, architects and others wanting to know whether
ivy could be safely left to grow on historic walls.
(b) Enhanced information dissemination about the potentially positive
roles of plants in conserving ruins has been underpinned by the
research as presented at two seminars in London which introduced the soft
wall capping research findings (2007) and the ivy on walls research
findings (2010) to large audiences (c 200 and 100 people respectively) of
conservation professionals (architects, surveyors, inspectors of
monuments) from English Heritage and cognate bodies. Speakers from the
research project teams outlined the aims, methods and scientific results
of each project. Points raised during the discussion were included in the
design of the second phase of each research project. Written versions of
all the presentations from both seminars have been published on-line to
make the results freely available to all [C5, C6]. Both projects
feature on the English Heritage website. The ivy project seminar report
was number 11 on the top 50 downloads from the English Heritage website
between Jan and May 2012, having been downloaded 1240 times.
The impact of these reports is evidenced by the number of enquiries from
conservation professionals wanting both further information and a chance
to input to the research. Follow up queries were frequent with well over
30 emails and other requests for advice received. For example, a
conservation architect, telephoned Heather Viles, in June 2009, after the
soft capping seminar to discuss the team's results in comparison with his
experiences at Thirlwall Castle and suggest new research directions [C7].
A building physicist also emailed requesting further information on the
ivy findings to help inform his conservation advice, saying `...Your
team's work could be of great interest to Building Physicists too. Ivy may
be a good solution to add extra insulation to new buildings...I am busy
with thermal simulations of low cost housing. Insulation made from oil is
expensive and my hope is that natural growth around buildings can provide
micro- climates that reduce the needed level of insulation.' [C8].
Further impacts from the research include invitations to give talks on
the research to a range of professional bodies, courses and meetings in
the UK and abroad, reaching a combined audience of well over 400
architects and conservation practitioners (e.g. the Stone Conservation
conference at the International Stone Show in London, Conservation
Masterclasses at West Dean College, APS Masonry in Oxford, Getty
Conservation Institute, Los Angeles, International Stone Deterioration and
Conservation Congress, Columbia University). The media coverage of the ivy
on walls seminar led to an invitation to submit a paper on the project to
a widely-read conservation publication (Viles, HA, Sternberg, T and
Cathersides, A. (2011) Is ivy good or bad for historic walls? Journal of
Architectural Conservation July 2011). As a result of an EPSRC KTS project
with Historic Scotland our research findings have also been incorporated
in their INFORM guides on `Biological Growth on Masonry: Identification
and Understanding' and `Growing Old Gracefully: Appreciating the
Appearance of Historic Masonry Buildings' [C9, C10].
Sources to corroborate the impact
C1: English Heritage: Building Conservation and Research Team and
Landscape Team leaders - will confirm the impact of the research on
English heritage conservation practice.
C2: Hailes Abbey soft capping project described in Heritage
Calling blogpost (24.4.2013) http://heritagecalling.wordpress.com/2013/04/24/turfing-the-walls-at-hailes-abbey/
and Pitchcare magazine (11.7. 2013) http://www.pitchcare.com/magazine/soft-capping-our-heritage.html
C3: Email from Gestionnaire de projets, Institut du Patrimoine
Wallon (21/9/2011) (held on file) confirms enquiry about the relevance of
the soft capping technique to Belgian ruins.
C4: Morton, T et al (2011) Soft capping in Scotland, Historic
Scotland Research Reporthttp://www.arc-architects.com/aboutus/documents/SoftCappinginScotlandVol1.pdf
C5: Lee, Z., Viles, H.A., and Wood, C.H. (eds.) (2009) Soft
capping historic walls: A better way of conserving ruins? English Heritage
Research Project Report, 69pp, http://www.english-
C6: Sternberg, T et al (2010) Ivy on Walls Seminar Report, 62pp, http://www.geog.ox.ac.uk/research/landscape/rubble/ivy/ivy-report.pdf
C7: Conservation Architect, Berwickshire - will confirm the
relationship between his conservation practice and the soft capping
C8: Email from buildingphysics.co.za (3/6/2012) (held on file)
confirms interest in ivy research and potential for ivy as an agent of
C9: Historic Scotland INFORM guides: a) Biological growth on
masonry: Identification and understanding (Jan 2013 Julie Eklund and
Maureen Young) http://conservation.historic-scotland.gov.uk/bio-growth-masonry-inform.pdf,
b) Growing old gracefully (Feb 2013, Julie Eklund and Katherine Hummelt) http://conservation.historic-scotland.gov.uk/publication-detail?pubid=9909
C10: Historic Scotland: Technical Conservation Team leader will
confirm interest in soft capping and ivy research findings.