Updating energy performance throws up a variety of challenges that require sympathetic solutions along with common sense.
Listed buildings have power: the power to focus development and create new places around them, but also to control change and limit fabric renewal.
This power has arisen as a result of long-developed legislation dating back to the late 19th century.
Yet historic buildings almost invariably do not conform to modern standards of energy efficiency.
So how is a sustainable balance achieved – one where energy demand is reduced but that still maintains our magnificent stock of more than half a million listed properties?
Historic works demand planning
The essential link between past, present and future for our valuable heritage assets, and in particular Grade I-listed fabric, is the conservation management plan.
This creates a plan with a holistic overview of the building and the opportunities for it to remain in beneficial use.
The CMP can be used to lay out a blueprint for fabric enhancement – such as system renewal, roof insulation and changes to windows – and assess this against the change to the historic fabric.
“It is essential to measure and understand the response of the building to the external environment before key design decisions are taken”
If the approach is not structured and logical, the project can fail in a number of areas, including unimpressive improvements to energy consumption and harm to the historic asset.
Building services are known to have a typical lifespan of 20 to 30 years and so any changes to historic fabric should, wherever possible, be reversible and capable of being taken out, leaving little trace of their existence, ready for the next phase of occupation.
Justifying the upgrade
Change is inevitable and this is accepted; the processes that exist in heritage protection allow for it; society and economic use evolve.
But there must be a good reason for making changes to any building protected by heritage legislation.
Professionals engaged to manage energy must understand the thermal performance before enacting change.
A visual inspection of the fabric and systems will not provide this and it is essential to measure and understand the response of the building to the external environment before key design decisions are taken.
This calibrates future change, especially if thermal modelling is undertaken.
“Knowledge of how previous services have been distributed is invaluable and avoids making unnecessary new holes and openings”
For example, those running Gorton Monastery – a 19th-century former Franciscan friary – wanted to create closer links with the community and build new facilities to aid this.
This aim was then coupled with a concern to pursue excellent environmental performance.
This greatly informed Ramboll’s strategy for energy use, which was as much a study as a project report, and provided advice on energy sources, fabric construction, airtightness, fenestration and the development of building services.
Most historic buildings have also had at least one generation of installed services.
Knowledge of how previous services have been distributed is invaluable and avoids making unnecessary new holes and openings.
New system design can also take advantage of knowledge of the existing fabric, gleaned by previous fabric dismantling or other architectural or structural work.
Inevitably the mention of fabric enhancement to historic buildings often brings conflict.
This deals with change to the visible, tangible historic constructions that society wishes to protect, whereas thermal performance deals with invisible movements of energy that society wishes to conserve. Somehow, the two have to be balanced.
While some parts of a building wear out more quickly than others and can be replaced without significant loss of fabric, many thermally significant parts of a building are also historically significant, visible from either one side or both.
“The case of New Court at Trinity College in Cambridge was extreme; a sensible agreement is normally reached long before this”
These include walls, windows and external doors. Reducing loss through windows has been a common area of conflict, often causing rifts between the owner or occupier and the local authority conservation officer.
The case of New Court at Trinity College in Cambridge, determined in 2014, was the first where such conflict has been driven all the way to vote by elected counsellors.
The result was the replacement of windows to a Grade I-listed building. This was extreme; a sensible agreement is normally reached long before this.
Maintaining an appropriate environment for both people and fabric is a delicate balance. The effect of poor environmental conditions on the fabric can often take a long time to manifest.
In contrast, people are usually very quick to complain if they are uncomfortable.
The monitoring of environmental conditions both before and after a project, identifying the character of the building in advance, responding to trends and re-balancing the system for comfort, enable the adoption of a common-sense approach.
This takes into account the existing performance of historic fabric and allows the most sustainable use of historic buildings.
A deep respect for fabric, a firm commitment to a sustainable society and a good dose of reason are required.
With this we can enact great change for both the benefit and enjoyment of our national heritage.
James Miller is technical director of historic structures at Ramboll