Background:
This iconic building in Halifax was designed by BDP and completed in 1974 as the headquarters of the Halifax Building Society. It was Grade 11 listed in 2013.
When built, the main office, designed with Burolandschaft principles, was elevated on four York stone-clad legs protruding through the diamond-shaped building, forming part of a complex roofscape. It included the main roof, a central core, two plant areas, and four raised octagonal roofs over director’s suites overlooking sunken courtyards.
The Trinity Project was a £116 million investment by the Lloyds Banking Group to refurbish this landmark office, which now acts as the main headquarters for the Halifax Bank, the area’s largest private employer.
The reconfiguration goal was to create a hub with fewer buildings, enhancing the experience for customers and staff. It turned it into a modern, sustainable office, blending contemporary design with original features like timber panelling, glass façade, and a 5×5 grid lighting system. The preserved York Stone façade maintains Halifax’s architectural heritage.
The roof covers about 4,500 m2 across four areas: main roof, metal deck, courtyard, and stair tower roofs. It includes flat sections with air handling units and perimeter railings. Some areas above four boardrooms feature double-height spaces, and new skylights were added to courtyards. The project involved removing old MEP equipment, upgrading insulation, and restoring a level 4 courtyard lost in the 1990s. Smaller roofs above stairwells were included.
Sustainability was central to the project, with the Halifax site now operating on zero carbon heating, using 100% renewable electricity, and achieving an EPC A rating. It also features three biodiverse living roofs and rainwater harvesting to boost environmental credentials.
Product Choice:
Main roof
Substrate – concrete, Screed – Permascreed, Priming – SIGnature fast drying primer
Air & Vapour Control Layer (AVCL) – SIGnature torch on with a polyester reinforced aluminium-cored SBS modified bituminous membrane, Insulation – tapered PIR insulation bonded using PU adhesive, Underlay – SIGnature Underlay25, Capsheet – SIGnature, Detailing – PMMA liquid
Metal roof
Substrate – metal deck overlaid with plywood, Priming – SIGnature fast drying primer, AVCL – SIGnature torch on with a polyester reinforced aluminium-cored SBS modified bituminous membrane, Insulation – tapered PIR insulation bonded using PU adhesive, Underlay – SIGnature Underlay25, Capsheet – SIGnature
Courtyard / green roof areas
Substrate – concrete slab, Temporary waterproofing – torch-on reinforced bituminous membrane underlay to primed concrete slab, Screed to falls – Permascreed
Priming – Permatec Polymer primer to cementitious substrates, Waterproofing system – permateec ecowrap incorporating permaflash-R reinforcement, Protection sheet –permaguard-F and permaguard-M to exposed up-stands, Insulation – enertherm XPS at a thickness of 180mm with u-value 0.18 W/m2K, Upstand insulation – enertherm XPS upstand board, Surface finishes – ballast and paving
Stairwell roof areas
Substrate – concrete deck, Priming – system compatible primer, system compatible AVCL,
Insulation – tapered PIR insulation bonded using PU adhesive, Membrane – PMMA liquid
Challenges:
A major challenge arose 12 months before work started when the initial plans differed
significantly from the actual roof condition. The roofing team and design team had to plan carefully to ensure the solution met schedule and budget constraints.
The original drawings showed a RAAC roof, intended to be replaced with a metal deck. However, inspections revealed the RAAC was built on sleeper walls over a 600mm void with a concrete slab below, leaving the substructure in good shape. This allowed the team to remove the RAAC and address the poor roof pitch and insulation needs.
The existing waterproofing, asphalt over RAAC and single ply membrane over metal deck, was in poor condition, with previous failed refurbishments. The roof suffered ponding due to inadequate falls and drainage, causing water to cascade over copings. The team needed to design a solution to improve water runoff and add outlets.
Removing RAAC also exposed asbestos, limiting inspection of some substructure parts, causing delays. Concrete kerbs and plinths beneath the RAAC required reworking the insulation design.
The project also required a durable waterproofing system that matched the York stone façade and allowed for more insulation, following British Standards. Collaboration with APiC UK ensured aesthetic integration of upstands with the façade and courtyards.
Workmanship
Originally, an inverted roof with ballast was planned, but due to a tight schedule and structural weight limits, a screed was used to smooth the deck, followed by cut-to-falls PIR insulation and a bituminous membrane.
To smooth the concrete deck, the contractors applied a mastic asphalt screed, which fixed level issues and provided temporary waterproofing for internal fit-out. They then re-sequenced the installation to start with the parapets, where RBM was installed first, allowing cappings to be fitted. Next, they prepared the surface by cleaning and priming before installing a AVCL, tapered PIR insulation with PU adhesive, underlay and capsheet. A third outlet was added to address standing water.
The build-up was finished with SBS modified bitumen membrane bonded by torching, with laps sealed with a bitumen bead.
For the central BMU posts, a robust waterproofing detail was created with mastic asphalt pitch pockets, followed by AVCL and a PMMA/mineral finish to match the roof.
On the courtyard roof, the team used a screed to smooth the surface and ensure drainage, then performed peel tests. After priming, they applied hot melt liquid, added a polyester layer, and completed with a second coat. Depth and integrity checks confirmed coverage.
In the stairwells, the original membrane was removed, and timber was prepared for vents to prevent condensation. Falls were created with tapered insulation, then covered with a PMMA overlay.
The final metal deck roof with rooflights was prepared by installing a plywood sheet and installing AVCL then tapered PIR insulation, followed by underlay, and capsheet.
Summary
The Apex Asphalt team working on the project were fully trained roofing contractors with hot melt permits and specific product training from system manufacturers and suppliers. Suppliers regularly assessed the work quality throughout and contributed to the project specifications, reassuring the client and main contractor of high standards. The expertise of both the contractor team and AccuRoof, part of SIG Roofing, ensured that the work met quality and modern performance standards.
