Background:

Glebe Primary School in Stockton-on-Tees caters for up to 437 students aged between 3 and 11. The building dates from the late 70s and features a complex mix of roof spaces. The school was suffering problems due to water ingress on certain roof sections. The areas covered 40m² on both the east and west toilet blocks and another larger roof area over the 350m² kitchen block that held a lot of plant equipment.

Following an inspection with a building surveyor and SIG Roofing’s specification division AccuRoof, it was discovered that the existing torch-on felt had reached the end of its serviceable life and there were problems relating to standing water. They also discovered a problem with the insulation, which in parts, hadn’t been adhered to the deck during the previous installation.

The decision was made to conduct a full strip-back of the roof to the substrate and then install a new torch-on felt roof system with enhanced insulation to bring the roof up to current British Standards. This project would be challenging for the roofing contractors due to the amount of plant equipment and the need to work to strict timescales implemented by the school for the work to be carried out largely over the summer holidays.

To bring the school roof up to thermal performance standards as required by Part L of the Building Regulations for refurbishment work, the existing insulation needed to be replaced and the levels upgraded. Due to insufficient falls and issues with standing water, the roofing contractor requested that AccuRoof design a tapered insulation scheme to introduce adequate drainage and bring the U-value up to 0.18.

The roofing contractor won the tender for the work through Stockton-on-Tees Borough Council with AccuRoof providing the specification and detailed drawings for the project.

Roofing product choice:

• SIGnature Fast Drying Primer
• SIGnature Torch-on polyester reinforced aluminium-cored SBS modified bituminous membrane
• SIGnature Underlay25
• SIGnature SBS Capsheet
• SIGnature RO Outlets
• SIGnature RO Parapet Outlets
• SIGnature GRP Trims
• SIGnature Tapered Insulation scheme

Specialist roofing contractor, Barclay Roofing, is a part of the AccuRoof Roofing Contractor (ARRC) scheme, which enables them to install systems supplied by AccuRoof, part of SIG Roofing. Contractors are only allowed to install their systems if they are trained by Accuroof in their products and are regularly assessed on the quality of their work by their technical team, providing the client and main contractor with peace of mind on the quality of the work.

Every member of the roofing team had received training from AccuRoof specific to the product they were installing. Their expertise ensured that the work was of the highest standard, meeting both quality and modern performance standards on this project.

Installation challenges:

Although installing the torch-on roof membrane on three fairly standard roof spaces was not a particular challenge for the experienced roofing contractors, it was the amount of technical detailing that made this project so complex.

The roof over the main kitchen area holds a lot of plant equipment. While most of it could be removed, there were areas where this wasn’t possible, which would result in the contractors having to navigate tricky detailing. One example was detailing to the extractor units which had been fitted to aid air quality in the kitchen below. This presented multiple issues and required the roofing contractors to strip the whole area back and replace it with new units. Existing pipework on the roof also added to the complexity, which required switching to alternative solutions. Originally, the contractors were hoping to conduct the refurbishment work and keep the pipes in place. However, once at the site, they realised that these pipes only ran about 100mm from the roof and would not work when installing the new tapered insulation scheme. Therefore, these pipes had to be raised and re-installed to allow for the new waterproofing system and insulation. In some areas the pipe couldn’t be raised due to existing glazing on the halls which required the roofing contractors to switch to a liquid for the detailing.

It was this same plant equipment that added another complexity to the project. The school wanted the work completed within the summer holidays. The roofing contractors were hoping to conduct the work and not have to remove the equipment, but this quickly proved unfeasible. The addition of hiring M&E contractors to decommission and remove the plant equipment added to the pressure on the timescales which would need careful project management by the roofing contractors. This was especially the case considering the school could not start the new term without the plant equipment being back on the roof.

Workmanship:

Work first started on the two toilet blocks which were about 80m² in total. This required stripping back the existing membrane and insulation to reach the plywood deck. While the plywood deck on one of the toilet blocks units was in good condition, the roofing contractors discovered on the second unit that rats had been going around the parapets underneath the plywood. Not only did this pose a huge health and safety risk to the school but it had also caused significant damage and required a replacement board.

Once the roof had been stripped, the roofing contractors cleaned the surface of any dust and debris. All areas were then primed with the SIGnature Fast Drying Primer. Once the primer had dried, the roofing contractor installed the SIGnature Vapour Control Layer, Underlay and Capsheet using a torch to ensure a minimum 5mm bitumen bleed on all laps. Insulation was adhered to the surface using a PU adhesive before torching the SIGnature Underlay25 on top of the insulation. The scheme was then finished with a torch-applied SIGnature Fire Rated AA Reinforced Bitumen Membrane cap sheet.

At the start of the school holidays, the M&E contractors accessed the site, decommissioned and then removed the plant equipment from the main roof section. The roofing contractors then identified that some of the existing pipework would have to be removed because it ran approximately 100mm from the roof and wouldn’t have worked with the new scheme.

When the existing membrane and insulation had been stripped the roofing contractors cleaned the existing plywood deck before applying the primer, VCL and PU adhesive. On the main roof, the roofing contractors worked on the tapered insulation scheme designed by AccuRoof. The insulation had to be installed exactly to the plan due to a complex set of falls within the scheme that required complicated valleys and gutters.

With the insulation in place, the roofing contractors installed the torch-on underlay and cap sheet working this up against the parapets which enclosed the roof. The one area that required a different approach was where the glazing sat next to the roof area. Here the contractors finished with a trim detail by fixing down the trim and then feeding the top layer of felt into the trim. Some areas of the roof had details which came through the walls, which couldn’t be removed. On these parts, the contractors switched to a liquid product for the detailing.

The M&E contractor then reinstall the plant equipment when the roof was completed, with a council-nominated contractor reinstating the pipework.

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