Dept of the Environment, Climate & Communications Headquarters

Background

In early 2018, the Office of Public Works (OPW) was tasked with providing a new headquarters for the Department of the Environment, Climate & Communications (DECC). The property which the OPW proposed as an appropriate fit for the DECC was Tom Johnson House. A six-storey 1970s office building located within the heart of the Beggars Bush military barracks in Dublin 2, Tom Johnson House was greatly in need of refurbishment and modernisation.

Brief

The DECC’s brief was for the OPW to design an office accommodation for 500 staff. This accommodation was to be a predominantly open-plan environment, balanced with bookable offices and meeting spaces for general use of staff. In 2018, the internal layout of the Tom Johnson House had become highly cellularised with long corridors that had no access to daylight or natural ventilation. The OPW architects identified these issues as a starting point for their design.

The existing building had a C3 Building Energy Rating. When the project is complete, it is expected to achieve an A2 BER – equivalent to the NZEB standard for new buildings. This will represent a reduction of approximately 75% primary energy use and carbon emissions annually. This energy rating has been achieved through the combination of improving the thermal envelope –by replacing the windows and insulating internally–while almost eliminating the buildings reliance on fossil fuels, with an extensive array of PV panels and air source heat pumps provided as renewables. At design stage, several iterations of thermal detailing were tested on all the key envelope interfaces in order to achieve the optimum u-values and psi-values of the target BER. The predominantly naturally ventilated nature of the building, a mixed-mode system managed by the BMS (Building Management System), further reduces the electrical load of the building.

Once complete, the OPW aim for this project to become an exemplar of deep retro-fit refurbishment. As part of this process, OPW will be carrying out extensive analysis post completion to review the performance of the building and to produce lessons learned from the project to inform future refurbishments.

Key Challenges  

A key challenge for this project was meeting was the huge emphasis on sustainability and the environment, given both the client and the projects target to become an exemplar of deep retrofit refurbishment. As a result, this objective influenced all decisions on the project, from the selection of recycled materials – for example the carpets, paint, furniture fabric & insulation were made from recycled materials – to the strict criteria applied to the project in relation to final building energy use – for example the newly installed pv system on the roof is designed to offset the entire electrical use in the building which includes all the building heating system which is entirely provided for by external air source heat pumps.

Compressing these complex modern services in to an existing 1970s structure was one of the key challenges of this project. Similarly, choosing to expose the existing concrete slab – to reduce on materials required for ceiling finishes – was one of the challenges of the project, as it meant compressing the new service runs in to very slender ceiling zones over the circulation. This challenge was overcome by carrying out regular BIM (Building Information Modelling) workshops with the design team in order to establish solutions in the virtual building model prior to constructing the solution on site.

Project Features

The most significant intervention which the architects have introduced is the creation of a new roof lit central void in the centre of the building. This newly formed atrium stimulates natural ventilation in the adjacent open plan offices spaces. Fresh air enters these spaces via the opening sections on the windows of the external facade. Automated timber shutters to the atrium permit cross ventilation in to the light well, where the warm air rises via the stack effect and exits through the opening sections of the newly formed glazed roof.

This new void also brings daylight down into the heart of the building and the adjacent open plan office spaces, where the previous long corridors had existed. The areas adjacent to the new atrium now benefit from daylight on two sides –both the external windows and the internal light well. Where the floor level has been raised due to introduction of a raised access floor, extra height has been gained by exposing the concrete waffle slab, which is now furnished with perforated timber inserts for acoustic dampening.

Along with the open plan areas, an array of different functions are arranged around the central void –an alternating configuration of double-height break-out areas and quiet rooms overlooking the atrium– which are linked by a new limestone stairway, which rises from the main reception area. A new public thoroughfare has been created at basement level, creating a continuous flow of space from the roof-lit atrium across to an existing sunken west-facing garden. This garden has never been accessible from the building until now, as a result of the replacement of the existing bay windows with full-height equivalents with bi-folding doors. Arranged around this thoroughfare, are a suite of meeting spaces for general use of the staff, together with a brand new 150 seater auditorium. In close proximity to the auditorium, is an existing precast concrete spiral staircase, which was previously enclosed in brick. As part of a measure to improve the width of access and daylight on this thoroughfare, this cantilever structure is now fully exposed, complete with a new curved glass balustrade.

The existing windows were in poor condition. Much of the glazing wasn’t original and other aspects such as the basement bay windows were unsalvageable due to water damage. The sloped brick cills showed instances of water ingress and were deteriorating from rain and dirt deposited on their sloped surface. The OPW design replaced all glazing with triple glazed equivalents, while the original brick cills were clad with new aluminium cills. The new typical window is composed of a central picture window between two opening sections. This takes full advantage of the panoramic views of Tom Johnson House, while externally, it provides further horizontal emphasis to the proportions of the facade.

This project is funded by the European Union under the National Recovery and Resilience Fund established during Covid-19 as a means of re-stimulating the construction economy. Included as part of the requirements of the funding, is adherence to the EU Taxonomy Requirements for Refurbishment Projects, such as the requirement for over 70% of non-hazardous construction waste to be recycled. The EU Taxonomy also imposes criteria in relation to reduced water usage and disassemblibility for future re-use of building components. All of these requirements have informed the architects’ design of the refurbishment, from the widespread use of timber, to the use of materials made from recycled content such as the aluminium cills, the carpet tiles, the paint and the insulation.