Allanton Primary School is of a timber framed construction with Pulverised Fuel Ash (PFA) blockwork and render finish. The PFA blocks have a high sulphur content which in turn has damaged the nails which fix the blocks to the building’s timber frame over time. This also meant that the render has started to spall and pose a risk to the pupils and staff. The safety of the staff and pupils was top priority so the school was closed in August 2021 to ensure that initial investigation works could be carried out and repairs completed as quickly and as safely as possible.

Working together with our Approved Installation Contractor, Procast, we decided to commence the Pre-Construction stage ‘at risk’ without the full substantiation and clarity that you would normally do with a project of this size and complexity but we were determined to overcome these challenges.

Emergency structural works and EWI cladding were required, which involved;

• Demolition and removal off site of existing masonry outer leaf
• Addition of cement particle board and fire curb membrane to existing internal leaf timber frame
• Installation of Structherm Structural EWI system
• Associated roof works
• Large volume of timber rot replacement and treatment works
• Asbestos removal works
• Replacement of all rainwater goods

This meant that the structural integrity was improved and the overall aesthetics of the building made it look brand new. During the works, the primary school pupils were temporarily relocated into another primary school meaning all resources, furniture and fittings were age and size appropriate and there was no disruption to their learning.

Before the installation of the External Wall Insulation, surveys were required to check the structural stability of the timber frame as the existing render had failed and as such, the timber frame suffered from water ingress and wet rot. During the surveys, it was found that there were infact four types of construction. This meant that Structherm had to produce different U-Value and WUFI calculations for each area.

Area 1 was a brick wall construction, therefore Structherm specified a Render Only system with a silicone finish to replace the existing.
Area 2 was a clear timber frame cavity with the existing blockwork to be removed and area 3 was an insulated timber frame where the existing insulation was then removed. They were then replaced with new 12mm Multi-Pro XS Board with Du Pont Tyvek Firecurb breather membrane. Structherm specified an SR125 Structural Insulated Panel which was then finished with a silicone finish for both of these areas.
Area 4 was of a concrete panel construction and as such this was decided to be left as is.

The four different substrates were a challenge when producing a solution due to the interfaces between each. Structherms design allowed the same specification to be used on all timber areas to keep it consistant.

One detail that the client had requested was to have the ability to refit the windows from the exterior in the future. This was a challenge for Structherm as the insulation usually wraps around into the reveals and sealed around the window frame which would cause issues when trying to remove the windows. There was the additional issue of existing sash boxes at either side of the windows which were being retained. The solution allowed the sash boxes to be filled with mineral fibre and a 12mm plywood installed over the top. The insulation was then stopped flush with the reveal by use of a stop bead and a powder coated aluminium closure piece was engineered which was pop riveted into the stop bead and fixed back to the new sash box cover. The closure pieces on the reveals allowed the client to remove the windows from the exterior and refit them to newly installed windows if required.

Another problem that Structherm had to overcome was the abutment of the Structherm SR125 system with the existing flat roof.
This area needed careful planning and sequencing to ensure that water ingress at this area was reduced. The use of a liquid plastic roof covering was installed onto the roof and up the adjoining wall which allowed the base tracks to be fitted and the Structural External Wall Insulation panels installed on top of these. This meant that the render was able to run around the flat roof, with use of trims, to reduce the risk of water entering behind the system. New gutters and downpipes were installed after the completion of the insulation system and rendering was complete.

The quick installation of Structherms SR125 system has shown an excellent example of refurbishment works. The school was in such a poor condition that it was destined for demolishing. The unique caged insulation system that Structherm has provided, means that the school was upgraded structurally and aesthetically and gives the school a new lease of life. The building is now futureproofed with the ability to remove the existing windows at a later date and install new ones without the need to relocate the pupils to other schools again. The installation of the structural insulation panels also mean that the school will now benefit from a better thermal efficiency which will help with the cost of running.

As a partnership with Procast and the Design Team we are absolutely delighted to have overcome all challenges in terms of design, budget and program to deliver this school back to North Lanarkshire Council for the pupils and staff returning in August 2022. The Project Team have managed to deliver this project for circa £670k which is well below the budgeted £800k, this is something we are hugely proud of.