Integrating the residential tower above the office floorplate introduced a series of complex challenges which required the greatest innovation. To avoid vertical support columns from the residential tower extending into the commercial floorplates below, the team developed a series of steel cantilevered trusses supported from the shared core between the tower and the offices below to support the residential floors which cantilever up to nine metres without the need for vertical support, while providing essential stability. This solution ensures the integrity of the office floorplates, and the basement car park beneath remain uncompromised.

Celebrating our role in bringing the client’s vision for College Square to life, the ACEI award judges commented: “The project illustrates the ability of structural engineers to innovatively solve problems in a way that allowed their client to realise the vision and ambition of this new landmark in the city. The design team at Waterman Moylan overcame substantial structural challenges and constraints posed in supporting the tower and the floor plates and in accommodating a new diagonal pedestrian route through the site.”

Click here to learn more about this stunning development.

Unlocking design potential

Climate resilience was high on the agenda, and inspired by this goal, our team provided multidisciplinary support for the scheme. Working alongside C+W O’Brien Architects, this saw our civil engineering specialists incorporate Sustainable Drainage Systems, including the provisions of green roofing, permeable paving, filter drains, green spaces and tree planting, throughout our design solution. Alongside this, storm water runoff is restricted to the greenfield equivalent rate, with attenuation storage provided to temporarily hold excess rainfall during large storms.

With an eye on minimising carbon-intensive waste, our structural design consists of multiple recase elements. This included a concrete frame of hollow core floor slabs, concrete cross walls above first floor level and an in-situ reinforced concrete frame between basement level and first floor level. At ground floor level, the 1,608 sq ft café, reception and shared amenity spaces required an open, spacious and column-free structural solution. As a result, our design included precast cross walls above first floor level designed as deep beams which minimised the need for reinforced concrete transfer beams within the structure, helping to maintain the open-plan layout below.

Due to extensive archaeological features and a high water table, the site required a carefully designed and managed piled foundation solution. To deliver this, a complex de-watering regime was developed and implemented during the basement excavation to avoid the ground water becoming contaminated by the excavation of the made ground.

Our electrical design brings together cutting-edge technology and functionality. A high-tech LED lighting scheme runs throughout the entire building, blending functional, decorative, and emergency lighting. These systems are controlled via DALI protocols and local presence detection, ensuring energy efficiency without compromising user experience. There is full access control coverage throughout the premises with CCTV both internally and externally adding additional security.

Heating and hot water are primarily delivered by two roof-mounted Air Source Heat Pumps (ASHPs), which feed into dedicated buffer vessels. The low-carbon solution handles the majority of the building’s thermal load and when required gas fired boilers and water heaters can supplement the heating and hot water systems. Each bedroom is equipped with individual humidity fans and heating controls, allowing tenants to tailor their environments personally. Communal areas benefit from a roof-mounted Air Handling Unit (AHU) supported by DX refrigerant condensers, providing both heating and cooling.

Designing a new icon

Working in collaboration with the client and architects our team delivered civil and structural engineering services from conception to completion for this significant project. Our specialists helped to shape one of the most sustainable buildings in Ireland, which is now home to the largest single office letting to take place in the European office market
since 2021.

Considering the proximity to the River Liffey, our structural solution effectively sealed the perimeter of the site to prevent the ingress of ground water as the basement excavation proceeded via a secant pile wall, with the piles extending into the underlying mudstone bedrock. To restrain the top of the piled wall, anchor ties were used, uniquely using glass fibre instead of conventional steel rods. This innovative choice was made to prevent complications during future excavations beneath surrounding roads, where the ties extend. In addition, internal propping was deployed to stabilise the wall adjacent to neighbouring buildings, ensuring structural integrity throughout the excavation phase.

The project team faced numerous challenges during enabling works and basement excavation, including the diversion and decommissioning of major buried services and
utilities. Close collaboration with the LUAS light rail system operator was essential to agree measures to monitor and protect the on-street rail line along the western boundary of the site. The formation level for the new pads and rafts of the two-storey basement lies deep within the mudstone bedrock strata and well below the tidal groundwater table. As a result, the basement has been designed as a fully water resisting structure, incorporating reinforced concrete walls and an integral White Tank System to ensure long-term waterproofing of the entire basement box.

For the commercial floors, the design team opted for a post tensioned concrete slab system, supported by a reinforced concrete frame. This proved to be the most value-focused solution, optimising slab depths and creating a more generous column grid spacing. The upper office floors utilise steel column and high-efficiency composite cellular beams around the perimeter of the setbacks, helping to preserve the internal column grid consistent with the floors below. This system also had a lower embodied carbon figure compared to more traditional construction, adding to the buildings green credentials.

A new diagonal shortcut has been created across the site, linking College Green to the River Liffey and Tara Street Station. This new route passes beneath the buildings, and above the clear span venue, acting as a wide covered passage opening onto double-height entrance lobbies to the offices, a venue reception, and a landscaped plaza at the centre of the site. To accommodate this, column positions were aligned so they did not fall onto either the access route or within the venue space. Four major column lines were allowed to proceed from foundation up to superstructure with the more minor columns supported on a series of 20-metre transfer beams at ground level. This strategy created an impressive double height subterranean space with the active plaza and
street passing above.

To achieve the architectural vision for the plaza at Tara Street with minimal columns, a bespoke six-storey high Vierendeel truss was developed. This structural solution allows the façade to appear as a large, unsupported 21-metre clear span.

The tower section of the development, rising from levels 12 to 22 above the former Apollo House site, was introduced through a later planning amendment that expanded the projects scope. Its location, offset from site boundaries and positioned directly above the vertical cores, meant it was structurally disconnected from the lower grid, with minimal opportunity to drop vertical elements through the commercial floors and basement below. To overcome this challenge, the design team adopted a highly inventive solution. Vertical steel cantilever trusses were strategically placed along the apartment party walls, which aligned consistently from levels 12 to 21. These trusses were anchored back to the central cores, allowing the tower to be supported independently of the lower structure. This enabled the tower to effectively ‘float’ above the commercial superstructure, minimising disruption to the base build. This incredibly ambitious solution was born out of the determination of both the client and the design team to enhance the architectural and commercial impact of the scheme.

Unearthing a glimpse of the past

Given College Square’s central location, extensive archaeological investigations were undertaken as part of the enabling works at the site. This uncovered the historic ruins of a structure which once served as a covert church for Catholics living in the south inner city. Detailed research led to the discovery that the church was first built on the site in 1709, in Penal times, when the practice of Catholicism was banned. These important discoveries were preserved, recorded, and carefully removed.

Commenting on this landmark regeneration’s impact, Waterman Moylan’s Associate, Anthony Byrne, said: “We are proud to have played a role in bringing this incredible development to life, creating a new icon for the Dublin skyline. The site’s location, history, and ground conditions meant that close collaboration across the design team was vital, and this led to a series of innovative design solutions. College Square has set a new benchmark for sustainability focused, mixed-use development in central Dublin, and this remarkable scheme demonstrates how a variety of building uses can be integrated successfully, even in the most constrained urban locations.”