5.7.1 As more results of the on-going intrusive structural surveys continued to show evidence of defective construction, it had become increasingly apparent that the lack of embedment of wall ties was present throughout the PPP1 school buildings. A more extensive scheme of wall tie remediation than was originally envisaged would be required.
5.7.2 At a relatively early stage following discovery of the extent of the problem associated with the wall ties, it was acknowledged by ESP, Galliford Try and Amey that it would prove impractical to locate and replace the required quantity of defective wall ties through opening up and rebuilding the walls. Accordingly, both Galliford Try and Amey had proposed to undertake a process of installing retrofitted proprietary remedial wall ties to all suspect areas of the external masonry walls of the schools.
5.7.3 This type of tie is installed from the outside of the building by drilling holes through the outer leaf and into the inner leaf of the cavity wall to the necessary depth to allow satisfactory embedment. The use of such ties had the advantage of being much less disruptive to existing brickwork and being very significantly quicker to complete than an approach based on locating and repairing defective ties.
5.7.4 A variety of resin-grouted ties, mechanically-fixed ties or helical screw-in ties are manufactured for this use. To ensure their effectiveness, it is a requirement of the manufacturers of these products that either specialist sub-contractors approved by them are employed to undertake the work or that any other tradesmen employed to do so have relevant experience and expertise, and have received specific training in the use of their product. There is also a requirement for sample testing of the suitability of the retrofitted ties using a specialist testing machine to undertake 'pull tests' to establish that the strength of the installed ties is satisfactory. The wall ties were satisfactorily installed in accordance with these requirements.
5.7.5 The installation of the wall ties was undertaken by sub-contractors overseen respectively by qualified staff from within Amey for Phase 1 schools and from within Galliford Try for Phase 2 schools. The design and specification for this work and the subsequent inspection thereof was undertaken respectively by WRD for the Phase 1 schools and Goodson Associates for the Phase 2 schools.
5.7.6 The use of the retrofitted wall ties had been agreed as an appropriate design solution by Scott Bennett Associates, acting on behalf of the City of Edinburgh Council.
5.7.7 On the 5th April 2016, ESP confirmed by letter to the Chief Executive of the City of Edinburgh Council that the schools could be safely reopened for the summer term as normal on Monday 11th April as they predicted that all the specified provisions, including wall tie remediation to the high-risk areas, would then be in place.
5.7.8 It was intended that a letter with this information would be made available to the staff and parents of children at the affected schools to reassure them that it was safe to re-occupy the schools. The key sentence within the letter from ESP to the City of Edinburgh Council was:
"The purpose of this letter is to confirm that, as we discussed at our meeting of 21st March, these buildings are safe for occupancy, and have been at every stage since the incident of 29 January 2016."
5.7.9 This letter from ESP was supported by a letter written on 4th April to ESP by WRD, their structural engineering advisers, advising them that in their opinion, as a consequence of the various remedial works undertaken and the creation of exclusion zones in all other necessary areas that all schools 'could continue to be normally utilised'.