I have always been fascinated by old buildings, both the way they were built and the way they have survived.
I had ten years off (working on new build alone with a different practice and to start a family) and came back to the world of conservation to find things had changed beyond recognition and so much for the better.
I believe good heritage engineers are a breed apart and will try to explain why.
The five “principles of conservation” that I follow are:
1. Conserve as found,
2. Minimum intervention,
3. Like for like repairs
4. Repairs should be reversible,
5. Repairs should be sympathetic.
(I know full well that sometimes these clash)
The "Its stood there for x-hundred years" argument certainly carries some weight, but the engineer has to consider changes in the building's environment and usage. For instance, we know rainfall intensity is increasing, and our knowledge of wind loadings has advanced in recent years. Trees grow and die, and in clay soils, can have a dramatic impact on a building's foundation stability. Mining and other sources of subsidence also need to be considered. Different usages affect not only loads applied to the structure, but changes in the thermal effects that can also affect the fabric, not to mention the impact of modern M&E services.
- Is it "tried and tested"? Tried and tested techniques are preferable to new methods that may have an unforeseen detrimental effect on the building at some time in the future.
- Is the repair technique reversible? Can it be taken out at a later date without significant damage?
- Are the repairs really required or will the building survive without them?
- Does the proposed work improve the overall structural stability of the building?
- What damage will be caused if these repairs are carried out?
- Will the repairs be seen?
- If they are seen, are they to blend in with the existing fabric or are they to contrast whilst still being in harmony?
- Will future historians be able to date the repairs?
- If there is a need to mix materials, what effects might this have?
- Will the building lose its inherent flexibility which enables it to cope with climatic changes without distress?
- Do the proposed methods meet the axioms "minimum intervention" and "conserve as found"?
Structural engineering for conservation is an art as well as a science. It takes little effort to design a major and intrusive scheme to deal with a perceived problem. It takes considerable expertise and experience to evolve a scheme that improves the condition of the structure which is unobtrusive and sympathetic to the historic fabric but which ensures that it has a sound future. It takes the same considerable skill to decide to do nothing.
It is essential for the engineer to accurately identify the source of the problem as many visible defects are merely symptoms of another problem, and not the problem in itself.
It takes experience and an understanding of traditional buildings to carry out sympathetic repairs to historic fabric, not just an ability with numbers.
Water ingress, lack of maintenance and inappropriate previous repairs/alterations are the biggest causes of danger to old buildings. Control of these could mean that you will never need an engineer.
I would like to think that the musings above will influence homeowners, developers and architects to select suitably experienced engineers for their projects.