From C3 to A2: a deep retrofit in Dublin 4

A 1970s office building in Dublin 4 would usually be seen as a demolition-and-rebuild candidate. On Tom Johnson House, the choice went the other way: a deep retrofit that kept the original structure and brought it up to a modern environmental standard.

AtkinsRéalis worked as the structural engineer on the project, which retained and repurposed the building’s original concrete frame and brick façade rather than replacing it. That decision preserved the embodied carbon already held in the structure, avoided the environmental cost of demolition and new construction, and extended the building’s design life by around 50 years. Reusing an existing building is where retrofit becomes a serious engineering task: understanding what can be kept, what has to change, and how to improve performance without the freedoms of a blank site.

Working through a protected archway

One constraint shaped almost every structural decision. Tom Johnson House sits within the former Beggars Bush barracks, where the only vehicle access is through a single protected stone archway. Every delivery, every piece of plant, and all the materials, in and out, had to pass through it. This influenced and dictated structural details, the size of fabricated steel elements, and even crane selection.

The centrepiece of the structural work was forming a new central atrium. To create it, the AtkinsRéalis team worked closely with the Architect and construction team to safely cut a light-well void through the existing concrete waffle slab. This involved installing trimming steel, propping each floor down to the basement, and saw-cutting the slab into sections small enough to crane out and transport through the site entrance archway. The atrium now draws daylight and natural ventilation into the heart of a building that had previously been a run of enclosed corridors with little natural light.

The measurable outcomes

The retrofit moved the building from a C3 Building Energy Rating to A2 (equivalent to the NZEB standard expected of new buildings) for a reduction of around 75% in primary energy use. Sustainability ran deeper than the rating: roughly 98% of construction waste was recycled, with demolished concrete crushed and reused as hardcore. The original waffle slab was left exposed with perforated timber acoustic inserts, avoiding the embodied carbon of plasterboard and suspended ceilings.

The building now serves as the headquarters of the Department of the Environment, Climate and Communications. This pathfinder retrofit resulted in a Dublin City Centre office houses the department, which leads Irish responsibility for environmental policy. The project was recognised at the RIAI Awards 2024 in two categories: Sustainability, and Workplace and Fit-out. It also won the Republic of Ireland branch of the IStructE Structural Awards - Medium project prize 2025.

What this says about careers in Ireland

Tom Johnson House shows the kind of engineering AtkinsRéalis delivers in Ireland: technically demanding and sustainability led. Deep retrofit asks engineers to combine structural judgment, building performance, and practical problem solving under real constraints and deliver work with visible value. For anyone considering a career with AtkinsRéalis in Ireland, this is an example of the work being done here today.

Read more about AtkinsRéalis in Ireland.