The online resource for the historic environment

2.07 Degrees of intervention

It is by no means appropriate to write off elements of an asset because they are old, show signs of decay or do not comply with today’s technological advances.
Respect for those simple facts may be considered a primary attribute of any conservation practitioner.

“...works which are original are better than those that are not.”
US Justice Souter: when assessing aesthetic worth in an American court.

Although that might be considered a sweeping statement, at odds with the principle of respect for all periods of intervention, it nonetheless encapsulates a primary tenet of conservation philosophy – that of minimum loss of authenticity by minimum loss of original fabric.

There is also the need to respect all periods of development, identifying each period of intervention and granting it true place and worth within the palimpsest of the asset’s development over time.

The choice of method, manner and materials used in any intervention project places a responsibility upon you to ensure that whatever you decide upon has been thoroughly researched and assessed as appropriate, creating least damage not only to the fabric of the asset but also to its aesthetic and historic value.

“The practitioner…must develop a critical and self-critical frame of mind, nurturing the ability to proceed from fact by way of logical argument to defensible – if not inevitable – conclusions.”
Earl, J.

New materials, their use and technology are constantly being advanced. Some new materials or processes may well be appropriate for use on or within the historic environment: Some may be positively damaging to it. You must be aware of these hazards when specifying materials, processes or methods. A full evaluation must precede any introduction of new materials or processes. See BS 7913: 2013 section 6.0 "Significance of Operational Repair and Other Interventions" see also 6.4 to 6.11 inclusive.

As an example of how modern building present problems of intervention strategy the work at New Hall (now Murray Edwards Hall) Cambridge following its listing in 1993 provides a useful study. The building was designed in the 1960s by Chamberlain Powell and Bon and pushed forward the then known technology of design and materials usage to new bounds. The building was listed Grade II* in 1993 when many of the elements of the original design were failing. The challenges are noted in "Conserving a 20th Century College" Preston, J.

Some of the issues to be considered were: failure of balcony windows in the residential blocks (Orchard Court) which were of flush design with no weathering. Choices would have to be made between replicating the original flush design of the windows, re-creating the same failure potential but retaining the original appearance, or replacement with different material (such as aluminium or PVCu), or, alternatively, adopting timber windows with weathering detailing with a concomitant risk of appearance change detracting from the original design.

Consider on what basis you would balance the factors involved and how you would decide between these options.

The City Council supported changing the material to maintain the original architectural detail and its aesthetic value. English Heritage insisted on the adoption of timber for the window replacement but with consequent changes in detailing

A strategy for intervention was produced as a Conservation Plan by Cambridge Architectural Research, and adopted by the College. This plan was supported by English Heritage and Cambridge City Council. The strategy provided for a shared framework of understanding, agreed assessment of significance and vulnerability, management policies and a basis for assessing individual challenges.

Some of the major works involved:

  • Major repairs to the dome over the Dining Hall.
  • New external servery
  • Replacement of all windows.
  • Covering of original ferrocement petals of the roof with insulation (both externally and internally)
  • New services in relation to mass concrete floors
  • New services and fire precautions provided as part of an integrated, surface mounted design
  • Failure of pre-stressed beams along the length of the library and carrying its roof
  • Failure of concealed rainwater system and the concomitant challenge of designing a sympathetic external system

All these challenges to the principles of conservation philosophy of minimum intervention, minimum loss of original fabric, minimum loss of authenticity and reversibility of intervention, provided the design team with massive dilemmas that were overcome by thorough analysis of the building its problems, aesthetic value and cultural significance and formulating an agreed strategy that permitted the building to be repaired with only the minimal impact that its problems permitted.

Identify some materials and methods in common use that would be wholly inappropriate for use in an historic context.

You may wish to consider why they are inappropriate particularly in respect of asset deteriology and longevity.

How might the above results be incorrect when dealing with Modern Movement structures.

Subsumed within the process of intervention will be factors more secular than philosophical. Such factors may be economic; loss of income during intervention works, insurance constraints following damage to structures. These factors and more will influence the method and manner of intervention and you must be aware of them and factor them into your intervention strategy.

“Conservation specialists have to work within current constraints but they must themselves be concerned with facts not fashions…”
Earl, J.

As a conservation practitioner you must be able to critically analyse possible solutions. You must be capable of critically assessing solutions that respond not only to the intervention brief but also satisfy the cost, technical and functional constraints of the client, but have minimum impact upon the historic environment. You must be able to argue the case for conservation, often against the requirements of modern legislation, societal impositions and, sometimes, against the wishes of a recalcitrant client. This will be the easier from a position of strength gained through knowledge and clarity of understanding of the historic environment and its importance to society.