New light through old windows

by Neil Storkes
NBS Architect/Technical Author

What is 'Constructive Conservation'?

The Shorter Oxford English Dictionary defines conservation as:

'The action of keeping from harm, decay, loss, or waste; careful preservation. The preservation of existing conditions, institutions, rights, etc. The preservation of the environment, esp. of natural resources.'

As a term, 'conservation' has an extremely broad meaning which encompasses almost anything that helps to ensure the survival of something of value.

With historic buildings, conservation starts with simple maintenance and repair work but also includes alterations and other proactive measures required to ensure the survival of a component. However, the concern is that every alteration erodes the authenticity of an object and can harm its character. So for any alteration to be considered as 'conservation' work, it must be limited to the minimum necessary to ensure its future and, wherever possible, be designed in a way that is 'reversible'. This policy of 'minimum and reversible intervention' lies at the heart of current conservation philosophy.

English Heritage's website states the following:

'...The aim is to recognize and reinforce the historic significance of places, while accommodating the changes necessary to make sure that people can continue to use and enjoy them.

The conservation movement has evolved from a reactive process, focusing on preventing change, into a flexible process of helping people to understand their historic environment and through that understanding, to manage change to it in the most appropriate way.

The best way to save a building is to find a new use for it. Even recently restored buildings that are vacant will soon start to degenerate again. An unreasonable, inflexible approach will prevent action that could have given a building new life...'

The result is a much more positive and proactive approach to conservation known as 'Constructive Conservation' actively promoted by English Heritage.

Energy efficiency

Over half of the energy used and CO₂ emitted from buildings comes from heating; in historic buildings the proportion is even greater. Historic buildings are subject to the same economics as modern buildings, and the significantly increasing cost of purchasing energy cannot be avoided. So the issue of improving the energy performance of these buildings is important, particularly if they are to have new uses, be attractive to investors and users, and remain economically viable. It is imperative that they become more energy efficient and are future-proofed against the various impacts of climate change.

Modern expectation of environmental performance requires that our buildings, regardless of age, keep their occupants comfortable without them having to wear thermal underwear and woolly jumpers and sleep in four poster beds with drapes. With regard to energy consumption and thermal comfort, the most obvious strategy would be to:

• Insulate the building envelope
• Reduce air leakage from the building envelope.

Richard Oxley and Peter Warm in their CIBSE Guide to building services for historic buildings, summarized the difficulties in improving the thermal performance of old buildings.

'In older buildings, it is not always easy (and sometimes not even desirable) to reduce the requirements for heating energy by adding insulation and cutting air infiltration...

Traditional buildings, including most historic buildings, tend to be of a solid-wall construction, built primarily with porous fabric that absorbs moisture, but also allows it to evaporate readily. This is often called the ability of the building fabric to 'breathe' - i.e. it has a low vapour resistance.

Older buildings are usually very complex structures, with a performance equilibrium that is highly sensitive to change. Modern methods of insulation, draughtproofing and environmental control should only be introduced after careful consideration, based on an understanding of the building and the materials that are proposed.

...reducing air infiltration too much can be damaging for both the building and the health of the occupants. Traditional buildings need ventilation not just to dilute pollutants and remove the normal moisture generated by the metabolism and activities of the occupiers, but also to carry away the moisture that evaporates internally from a 'breathing' structure'.

If the options of significantly improved thermal insulation and airtightness are not available in many older and particularly historic buildings, then more imaginative solutions are needed. Renewable energy technologies can be located locally to older buildings without directly affecting the building fabric. However, these will not have a direct impact on comfort levels, but they will offset the costs of maintaining those comfort levels. The location and surroundings of such buildings will also have a major impact on the opportunity for the remote siting of renewable energy technologies.

A team from Sheffield University has recently published an assessment of the potential for 'green roofs' as a passive cooling technique, and suggests that this is a good option for retrofit projects. The Sheffield University researchers have concluded that older buildings with poor existing insulation will benefit most from a green roof because it will achieve high levels of insulation unattainable by conventional means. ('Green roofs; Building energy savings and the potential for retrofit,' by H.F. Castleton, V. Stovin, S.B.M. Beck, and J.B. Davison is in Energy and buildings, available online at www.sciencedirect.com.)

Industry research suggests that both green roofs and green/ living walls can prevent incoming solar radiation from reaching the building structure, thereby reducing solar heat gain in summer; also reducing heat loss in winter by providing insulation and shielding the building fabric from prevailing winds. Both can also be used for other benefits including grey water recycling and the mitigation of the effects of increasing levels of rainfall. Living walls can also be used to improve the air quality in buildings, removing or reducing the need for air filtration and air-conditioning.

Green roofs have a direct impact on an existing building's structure and therefore may not be an option for some older buildings. However, green/ living walls can be independently supported to provide shielding to older buildings, so may be an option for serious consideration?

Despite the recent introduction of more stringent construction legislation, the Disability Discrimination Act and the Building Regulations (England and Wales) Approved Documents M Access to and use of buildings, and L Conservation of fuel and power have all taken a reasonable and pragmatic approach to 'improvements' to historic buildings. The recently published Approved Documents F and J, together with L1B and L2B (due for implementation in October 2010) have furthered this reasonable approach by including not only listed buildings, buildings in conservation areas and scheduled ancient monuments but also three further classes of buildings where special considerations in making reasonable provision may apply:

• Buildings which are of architectural and historic interest and which are referred to as a material consideration in a local authority's development plan or local development framework
• Buildings which are of architectural and historic interest within national parks, areas of outstanding natural beauty, registered historic parks and gardens, registered battlefields, the curtilages of scheduled ancient monuments and world heritage sites
• Buildings of traditional construction with permeable fabric that both absorbs and readily allows the evaporation of moisture.

The requirement is that when undertaking work on or in connection with these buildings, the aim should be to improve energy efficiency as far as is reasonably practical. The test is that work should not prejudice the character of the host building or increase the risk of long-term deterioration of the building fabric or fittings. However, older buildings that do not achieve the above criteria do have to meet the requirements of the Building Regulations when any redevelopment or significant refurbishment work is undertaken.

Conclusions

The main thrust of current thinking and strategy with regard to reducing CO₂ emissions in the construction industry has focussed very much on new buildings, and continues to struggle with the problem of how to significantly improve the performance of existing and retained building stock.

As the focus moves from the consumption of generated energy to embodied energy, the debate about the retention and refurbishment of buildings rather than their demolition becomes more critical. It is increasingly being appreciated that the refurbishment of existing buildings (not just historic buildings) particularly with minimal alterations is a more sustainable and therefore a more preferable approach than demolition and reconstruction.

If we are to successfully adapt our existing building stock to meet the increased environmental performance standards required by the construction regulations and also by the marketplace, it is essential that we understand how these older buildings work and what we can safely do to them without prejudicing their future. In many cases, as an industry, we also need to relearn about traditional building technology and materials.

It is also important, particularly with our historic building stock, that Constructive Conservation is just that – 'constructive' – and that opportunities for the implementation of new and sustainable technologies are encouraged, rather than having a return to the old reactive conservation process, focusing on preventing change. There is hope – consider Urban Splash's scheme for the Park Hill development in Sheffield, Europe's largest listed building!

Potentially, Constructive Conservation and the building conservation industry have much to teach us all!.

Related NBS information:

Articles:

• Regenerating historic buildings - legislation
• Grade listing of buildings

Selected links:

• Building conservation
• Owning period properties

Written July 2010

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