There is a wide variety of ‘future conscious’ ways to retrofit historic buildings, enthuses Alan Chandler. He helped put together the RIBA's recently published Sustainable Past and Future Guide, which provides guidance on how to sustainably renovate heritage buildings, while showcasing several inspiring case studies.
Chandler is co-chair of the RIBA Conservation Register, and Dean of Research at the University of East London’s Department of Architecture & Visual Arts. Conservation projects, he points out, vary from building to building, each one with its own history of previous interventions. So there are no one size fits all strategies as such.
However, the case studies do display notable aspects in common. An appreciation of how traditional materials are often more sustainable than their synthetic contemporary equivalents is one, and an understanding of the need to retain as much of the existing structure is another.
One of Chandler’s own projects is included: ‘Writer’s House’ is a featured renovation of the Grade II listed, late-Georgian home of a writer in north London. The work, recently completed, demonstrates the amount of investigation that conservation architects will typically carry out before arriving at a preferred solution.
Understanding moisture and ventilation
The house had previously had three separate post-war tanking systems applied for waterproofing at ground level in evidence, all of which had failed. Chandler describes this renovation work as having been catastrophic from the point of view of moisture management: it had generally served only to trap water within. Understanding moisture and breathability is a key aspect of any retrofit project, and the RIBA feature How to get a building retrofit ready explains the basics.
Digging an exploratory pit to investigate a vented cavity at ground level revealed the original flagstone floor of the scullery. Once exposed, the flagstones could dry out naturally again as originally intended.
Further investigations revealed a vented cavity that isolated structural walls from raised ground levels. Chandler abandoned his original plan to use a vented membrane system for the internal wall face; instead, he decided to allow the original vented cavity to do its job again.
Ventilation is augmented overall, however, by a mechanical ventilation/heat recovery system (MVHR). The air change strategies are designed to allow the physics of water movement through traditional materials to work once more, Chandler explains.
“It was about working within a very protected environment that imposed key limitations on what was possible, with vapour openness driving the agenda,” he states.
The effectiveness of traditional materials
“We are particularly happy about how traditional materials have dealt with moisture ingress,” continues Chandler. “It seems our use of Roman cement and lime plaster with bespoke ventilation is doing what the tanking systems failed to do.”
The house had gained an inset roof terrace in 1969. Removing this allowed the roof to be insulated with carbon-positive bio-based insulation materials: recycled cotton and wood fibre panels.
Sarah Khan, Partner at Roger Mears Architects, notes that she has experienced positive changes in attitude towards the use of traditional materials over the last few years: between, in fact, the two case studies from her practice that feature in the Sustainable Past and Future Guide.
The first is a Grade II listed cottage in Camden; the second is the renovation of two derelict Gothic Revival chapels in Putney, including the conversion of one into a home. Awareness has grown, she has found, among clients and more importantly among local authority conservation officers.
“Previously, nobody wanted to sell us their products because they had not been tested in these kinds of situations,” Kahn remembers. “That has already changed. There are now more products available, better software to model their effects, and guidance is catching up.”
Negotiating a compromise between heritage and sustainability
While stripping out plasterboard to expose the original internal fabric in the Camden cottage, it was found that different construction methods had been used in every wall, necessitating a differently detailed insulation solution each time. As with Alan Chandler’s Writer’s House project, it was a case of figuring out bespoke solutions as the project progressed.
In the case of the Gothic chapels, the dereliction required a heritage study and a later carbon study. Even so, the retrofit is rated as deep as possible, given the chapels' heritage constraints.
Compromise when improving the energy performance of a building with a wealth of heritage detail is inevitable. External wall insulation was out of the question for the chapel. Inside, a way had to be found to improve wall insulation without compromising a series of carved head details.
Project architect Alan Brown opted for wood wool finished with lime/hemp insulated plaster tapering off towards the carvings. Insulation thickness was dictated by the need to achieve good comfort levels, rather than epic U-values that would have buried the carvings.
Large tracery windows presented another challenge. Recent guidance from Historic England follows the general principle that reversible retrofit measures are acceptable, Khan explains, so secondary glazing has become a typical solution. Even so, the secondary glazing used for the chapel had to be carefully designed to fit within tracery details.
Use of renewable energy
Chandler says renewable energy and low temperature heating systems have risen to the top of the list of subjects that architects working on heritage retrofits need to learn about, due to dramatic rises in energy costs seen recently. There is a new urgency in finding ways that historic buildings, which rely on moisture- and vapour-open construction, can work with low carbon energy systems.
He reports that he has been looking at putting solar panels on the tiled roof of some historic almshouses he is working on, where once he would not have considered it. The elderly residents who live there say they simply cannot afford their energy bills.
It is a dynamic situation, he argues, and one that will create an ongoing need for sustainable conservation CPD – and plenty of shared case studies - in the future.
Do you have a passion for conservation architecture? Do you want to develop specialist knowledge, skills and connections in the field? Learn more about today's conservation issues with the RIBA's upcoming conservation CPD series, which begins on 16 March.
Thanks to Alan Chandler, Director of Arts Lettres Techniques and Dean of Research at University of East London’s Department of Architecture & Visual Arts; Sarah Khan, Partner, Roger Mears Architects.
Text by Neal Morris. This is a Professional Feature edited by the RIBA Practice team. Send us your feedback and ideas.
RIBA Core Curriculum topic: Sustainable Architecture.
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