The property is a grade II listed building located in Accrington Lancashire, originally the property was Christ Church School Hall, which was converted into apartments, in the early 1990s.
The gable elevations are of a 600mm thick sand stone rubble infilled construction. The roof is of a traditional queens post truss and purling construction, which take their bearings from the gable elevations and queens post trusses, which in turn take their bearings from the north and south facing elevations, under a natural slate covering.
The gable elevations were causing concern, due to an outward lean on the east gable and distortion to the lower central area of the west gable. An outward deflection of 90mm in the vertical plane was also found to be affecting the North elevation, when scaffolding was finally erected. Olympic Construction were contacted by Consultant Engineer Roger Westbrook, to provide costs and specification for a structural stabilisation system which could be installed and would be acceptable to the conservation officers.
The first issue which had to be overcome was access, as the roof gutter line was eight meters from the ground and the area below was now residential apartments, access would need to be gained from the external, once inside the roof void we had to make a safe working platform, to construct two mobile scaffolding systems to allow access to the upper areas of the roof which were a further seven meters high, health and safety on this job would be of paramount importance.
Photograph showing external view
To conform to conservation requirements, we had to provide a specification to stabilise the structure of the building, which was sympathetic to the building structure and preserve as much of the historic building fabric as possible, the stabilisation specification was designed by our surveyor Adrian Dawson, who used the existing structural elements of the property to restrain and stabilise the structure and cause minimum damage, but most importantly, if required could be completely removed from the structure in full, so allowing the property to be returned to its original condition without causing any major damage, site meetings were held with all parties concerned and the specification was agreed.
To stabilise the gable elevation a timber framework was constructed within the roof structure, using 6m 100 x 100 section timbers to form a structural frame, these connected the existing queens post truss and the purlings where they took their bearings from the gable elevation, with 200mm coach bolts.
Photograph showing constructed framework within roof void.
To fix the gable elevations to the constructed framework, the 600mm external elevations were drilled and lateral restraining ties were installed at 600mm centers along the apex and horizontally at the purling levels, in total 140 ties were installed and tested.
On closer inspection of the external structure from the scaffolding, it was found the coping stones to the East gable elevation had slipped by approximately 40mm, this had resulted in the kneeler stone which holds the large coping stones in place rotating outward, presenting a risk of this being displaced, which presented a dangerous situation, the pointing to the upper East gable being in a very poor condition.
his presented further logistical problems, due to the weight of the coping and kneeler stone sections which were estimated to be around 500 kilograms, to address these issues the scaffolding needed to be adjusted and strengthened to be able to take the weight of the additional stonework and jacking system, which needed to be used to maneuverer and relocate the stonework.
The Coping stones were first fixed with stainless steel dowels to prevent any further slipping of the stonework, the base cooping trimmed to allow the resetting and fixing of the kneeler stone, this having to be maneuvered back into location using hydraulic jacks, this then being fixed to the existing stonework with stainless steel pins and resins.
Samples of the original lime mortar were removed from within the wall structure, this was sent off to be analysed and was identified as ‘Fox cragg’ this was made up as a premix by the suppliers for continuity and delivered to site, the upper gable elevation being repointed to ensure water tightness of the structure.