SUPPORTING COLUMNS
Restoring a Georgian house in Jersey
Structural engineer Brian Morton describes how an alternative was found to a drastic proposal that would have rebuilt everything within the house’s external shell.
The conservation officer
was worried about the front
wall’s backward lean.
roof, rather than the original flat roof over the centre section. Internally the partitions and external walls were completely panelled, and the ground and first floor had lath-and-plaster cornices to ceilings, all of the original date. The panelling throughout the building, and especially the front and rear walls, was in a poor state. Some needed to be replaced but generally it was repairable.
The conservation officer expressed concerns about the backward lean of the property’s front wall. He asked the usual question as to whether the building was indeed restorable and whether the panelling could be conserved. I was able to reassure him that I did not think that the lean on the front wall was of recent origin. My view is that it was either built with that backward batter or the wall must have settled during the early years of its life. I was able to draw this conclusion because the open gable end had been rendered with hard cement, with absolutely no signs of any significant cracking, suggesting that if there had been foundation movement originally, it had long since stopped.
In my report I drew the conclusion that the building was indeed restorable. We simply needed to carry out a much more detailed inspection of the condition of the timber main beams and the ends of the timber roof trusses where they were supported on the front and rear walls. But we reached agreement that a specialist archaeologist should be asked to inspect to establish the importance of the structure.
Not unusually, I heard nothing more about the building for about two or three years. Then I was sent a report by a local firm of engineers who had estimated a cost well in excess of £1 million. They indicated that the only possible way of retaining the building and restoring it would be to gut it internally completely. This would involve taking it apart piece by piece, removing panelling, carefully carting this away to workshops, taking up the floors, taking the beams away, repairing them off site and bringing them all back. In other words, leaving just the external shell and rebuilding the interior completely, putting back everything in its original position and, effectively, re-making every part where necessary so that the building would go back to its original form. I did not accept that it was necessary to carry out this massive amount of work.
While I was not in touch with the situation, Warwick Rodwell, historic building archaeologist, had carried out a very detailed inspection of the building and reported. He agreed with my philosophy. Negotiations were taking place with the National Trust for Jersey, which was trying to acquire the building and was, ultimately, successful.
Some five years ago I was asked to survey a georgian house in Jersey which was registered (listed) and considered by the government conservation officer to be of great importance. The house, with a simple rectangular plan, was a structure of two storeys, with accommodation in the roof. It had suffered from a lack of maintenance over many years. Water had penetrated the structure, mainly from leaking gutters behind the parapet on the front and rear elevations.
The enclosing shell of the building, mainly of almost rubble stone construction, was generally in a reasonable condition. One exposed gable wall had been rendered, while the other gable formed a party wall with the adjoining building. The front and rear elevations all suffered from water penetration to the timber lintels. This had allowed some cracking to the brickwork over the windows. There was clearly a need to replace all these lintels during any repair process.
The structure of the house was quite simple. Major timber beams spanned the building front to back, and secondary joists spanned between them and on to the gable walls down their length. The staircase enclosure was supported off the main timber beams and timber stud partitions. at roof level the structure was again principal trusses spanning the width of the building. These were originally truncated, but they had been extended by further rafters to provide a pitched
CONTEXT 97 : NOVEMBER 2006
The Morton Partnership was appointed by the National Trust to act as engineers for the project. a conservation architect was available to advise us when necessary. I was advised that it was likely that the National Trust’s own workforce would carry out the work to the building. This I very much welcomed because it was going to be a project that would be very difficult to cost, as so much of the work would depend on what was found as the floor beams and roof beams, particularly, were exposed.
I suggested that the way forward was for me to prepare a very detailed schedule of work, estimating as far as possible the extent of repair necessary to elements of the building. following my initial inspection at this stage, I satisfied myself that the building’s problems simply related to the water penetration above the front and rear walls, which had affected all the timber supported on those walls to varying degrees. I felt that we should support the central structure of the building so that we could splice on new ends to the substantial principal beams. However, before that we would need to check and structurally strengthen the principal trusses, working from the top down.
The schedule of work was carefully costed by a quantity surveyor who arrived at an overall figure of about £650,000, based on my schedule, with professional fees to be added. It was on that basis that the National Trust acquired the building and asked me to act as engineer, guiding the National Trust workmen through the project.
This was an ideal situation. We gradually opened up the roof, and put forward initial proposals for repairing the ties to the roof trusses and the principal rafters. We were able to further work with the National Trust workforce, providing details of strengthening necessary to the internal birdcage scaffold, so that the trusses could be hung from this scaffold during the repair process. This suspension system was also used to lift the trusses and ultimately the floor beams, thus dealing with the compression of the timber beams that had occurred at their ends due to water penetration, allowing them to settle over the period when the building was unoccupied.
One of the problems associated with the original construction and the subsequent deterioration related to the outward spread of the roof. We dealt with this by various specially configured stainless steel brackets. These ensured that the wall plates were restrained and the rafters were fixed adequately. We quickly established the principles of the repair to the timber trusses and beams, allowing the carpenter/joiner foreman to follow the same principles all the way through the project, dealing with urgent matters by telephone and fax.
The building control section of the government accepted that we were simply repairing the building, so building control consent was not required for our work as long as we sent to them details of our proposals and we ultimately confirm our satisfaction with the finished project. The conservation officer accepted the approach that we had taken, and apart from his casual
The original state of the roof timbers
Water penetration had affected all the timber supported on the front and rear walls.
The repaired roof trusses
visits to carry out inspections we were able to proceed without any difficulty.
The methodology used to carry through these repairs successfully was related to our detailed inspection of the building and our realisation that the problems were simply associated with the front and rear walls, and the water penetration in those areas. although this had affected the internal structure, dealing with the end of the principal beams provided a good basis for the remainder of the project. Our original view that the cracks in the structure were due to defective timber lintels was clearly correct, there being no evidence during the building work of any current subsidence.
a conservation architect appointed by the National Trust is now carrying the project through to a satisfactory conclusion, based around the archaeological studies and his assessment of the extent of repair and replacement necessary to the panelling. The National Trust has been acting as a very enthusiastic client, with a very experienced hands-on site agent working with a small team.
Brian Morton MBE is a consultant to the Morton Partnership, a practice he formed in 1966.
CONTEXT 97 : NOVEMBER 2006