Dublin boiler house reborn as green building exemplar

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60% energy reduction

Building: 1960s masonry boiler house retrofitted to become sustainability centre
Completed: December 2016
Location: Ballymun, Dublin 9

BER: A2

When the Ballymun Boiler House opened in the 1960s, it was by far the largest mass heating system in the country. It not only provided district heating to nearly 2,800 families, it also pumped fresh water directly to the newly built residential towers, obviating the need for local booster pumps.

Fifty years later however, with the flats demolished, the boiler house had fallen into disrepair and the site itself had become a dumping ground for construction waste. It was overgrown in places and contaminated by oil in others.

In 2013, Dublin City Council, Ballymun Regeneration and the Rediscovery Centre began a project to reinvent the site and create something unique in Ireland. The rejuvenated building would become an exhibition centre for sustainability and a home for the Rediscovery Centre – a grouping dedicated to providing community employment and training through a collective of innovative reuse enterprises. The design would exemplify sustainable refurbishment and showcase a wide range of green technologies and building methods.

Funding was secured from both the exchequer and the EU’s Life and Environment Fund, and a lengthy design phase, led by ABK Architects, began in 2014. Main contractor Purcell - who draw from a vast experience in delivering high profile sustainable buildings, including a passive house school for the Department of Education in Moynalty, Co. Meath profilde in issue one of Passive House Plus - were appointed, and work started on site in January 2016. Ballymun Rediscovery- Centre opened a year later. The centre has been designed to ensure a minimum carbon footprint both in construction and throughout its life, while the structure features a very broad range of sustainable elements.

The layout sets out to make best use of existing features and to optimise solar gains, while accommodating an improbable range of technologies including an air-to-water heat pump, a stove fuelled by an onsite willow plantation, and a combined heat and power unit (CHP), as well as both solar thermal and photovoltaic panels – a variety that would look excessive were it not for the role of the building as a demonstration project.

This article was originally published in issue 22 of Passive House Plus magazine. Want immediate access to all back issues and exclusive extra content? Click here to subscribe for as little as €10, or click here to receive the next issue free of charge

There’s rainwater harvesting and green roofs, composting toilets, a liquid waste reed bed water treatment system as well as a long list of sustainable and reclaimed building materials. Perhaps the most fascinating element of the build has been the way in which the design and build teams sought to minimise waste and create the new building out of the old.

Robert Davys of ABK Architects says that a core ambition of the project was to demonstrate the environmental value associated with building reuse rather than demolition. “A key stage of the design process – and critical to the project’s success – was the identification of original building fabric and contents suitable for reuse.”

There are two headline elements here worth mentioning. The team found a way to retain both the original concrete slab and the main steel structure. Davys calculates that this action alone resulted in the avoidance of 55 tonnes of embodied carbon – and that’s based purely on production impacts, without considering either disposal or transport.

This same ethos was maintained throughout the project. The original building included aluminium louvres which at one time helped to dissipate the excess heat generated by the Boiler House’s three 35 tonne boilers.

“We saw aluminium louvres and thought that we could do something with them,” says Davys, “so we came up with the idea of cutting them, rebending them, then using them to make aluminium shingles, which were then installed on the façade.”

He explains that the process of choosing construction materials was based on an ordered prioritisation. First priority was given to materials salvaged from the boiler house itself. Next in line came building materials available locally from other building or demolition sites. Third were sustainable, natural, renewable materials or those made from recycled waste. If none of these streams provided what was required, materials with excellent thermal performance, low embodied carbon and environmental impact were chosen.

Making maximum use of the onsite materials required a great deal of flexibility on the part of the design and build teams. “It’s a difficult thing when one has a desire to recycle and reuse, because you’re never entirely sure of what you can reuse and recycle, even up to the detailed design stage.”

For example: The roof deck of the old boiler house included a bituminous membrane mounted on softboard. This was not a material that the design team would have chosen to include, but at the same time, getting rid of it would have created a negative environmental impact. The decision was then taken to try to reuse it as a vapour barrier in the new build up.

“In principal, that sounded fine and quite a clever sidestep,” says Davys, “but in reality, when you got down to the demolition and started pulling some of this stuff up, we found that it was full of holes, while the softboard underneath was saturated. To reuse it would have meant trapping a whole load of moisture in the building.”

Often, a third way had to be found in order to retain materials that weren’t quite up to the job they had originally been installed to do. Most of the decking used on the old boiler house was aluminium, and lacked sufficient resistance to retain the new fixings. Instead of ripping it up and throwing it out, OSB board was used together with expanding anchor rivets to strengthen it.

The project also features brick, timber, windows and even sheeps wool insulation salvaged from local demolition sites (though the notion that any buildings fitted with sheeps wool are being demolished warrants further investigation, given how comparatively recently the material has entered the supply chain.)

One of the Rediscovery Centre’s reuse enterprises is Rediscover Paint. There, old, non-hazardous, water-based paints are collected from the public via recycling centres, then remixed and offered locally – and affordably – to residents and community organisations. This salvaged paint was used throughout the centre. Furniture and fittings that had been destined for landfill were also upcycled and reused. And of the three original 35 tonne boilers, one was retained as a ‘symbolic vestige’ of the original function of the building, while the other two were sent for recycling.

The design team had originally envisaged that recycled railway sleepers would be used to demark the kitchen garden. When these proved costly, the team took a fresh look at the site and ended up cutting up and re-using some of the boiler house’s old steelwork.

This approach permeated all aspects of the design, not just the selection of materials. The building itself is a large, single volume, into which an additional floor was added during the construction phase. The site also features an adjacent, disused concrete reservoir.

“When we looked closely at the scheme we realised that the top of the buried reservoir on the site was more or less at the floor level we were adding into the building. Originally, there was a notion that we would clear the reservoir to make way for the kitchen garden, but instead, we decided to make a bridge from the new first floor level out to the top of the reservoir.”

This provided an exhibition route that allows tour groups coming through the building to cross the bridge to the garden area, then descend the constructed slope at the other side.

Part of the brief was to create a ‘3D Textbook’ which would use the project as an educational tool, with the ultimate aim of inspiring behavioural change in everyone who passes through its doors. This motivation led to one of the central challenges of the build. If the designers had focused exclusively on creating a comfortable, healthy environment using sustainable materials, the palette of elements and technologies would have been kept tight and efficient. Instead, a range of complications were designed in.

“Normally,” says Robert Davys, “keeping the heat in and the water out are two primary concerns in a building and you might use five materials to achieve this, whereas here, we had closer to fifty. With all of those different materials and different junctions, it was quite a head strain to make sure all the detailing was correct.”

In order to tie the disparate elements together, certain common materials were deployed. First among these was hempcrete.

Composed of hemp and lime, hempcrete provides structural strength, first and foremost, but it also acts as a vapour permeable insulator. It was used in the south and east facing walls of the centre.

By using hempcrete, the team avoided high embodied energy alternatives such as concrete blocks and cement, or indeed petrochemical insulants. Davys points out that despite the fact that hempcrete has been used in structures across Europe for the past ten years, the Rediscovery Centre is the first public building in Ireland to use this material.

Compared to virtually all of the buildings published in Passive House Plus, the U-values are relatively modest. In some ways the building is an inversion of the passive house approach – where the emphasis is on passive approaches to meeting heating needs, combined with mechanical ventilation to ensure good indoor air quality while recovering precious heat. In this building, it’s fair to say there’s more emphasis on sustainable mechanical technologies to heat and power the building, with passive approaches to delivering indoor air quality. It will be fascinating to see how an attempt at low energy building that’s so conceptually different from passive house performs over time.

M&E engineer Brian Homan of Homan O’Brien acknowledges that the broad suite of heating technologies were installed primarily for demonstration purposes, adding that all have been fitted with sensors and recording devices to keep a close watch on how they perform. As yet, the data collected hasn’t been subject to detailed analysis to establish whether the building performs to its ambitious targets: Homan O’Brien used dynamic modelling and simulation to prove that 80% of the building’s energy use would be generated on-site. (IES simulation software was also used to predict daylighting, natural ventilation and overheating levels).

One of the big challenges from Brian Homan’s point of view centred on achieving the right balance of efficiency and thermal comfort from the variety of systems as the seasons pass.

“Now that we’re into the summer, the PV panels are going to start coming into their own, and we might no longer need the CHP, while the solar thermal will be generating hot water – so at this time, it’s getting the right balance between CHP and solar.”

The building is ventilated passively, via windows at high level which can be triggered to open automatically. This system is supplemented by some mechanical ventilation in toilets and workshop areas – particularly the paint recycling centre which would have a requirement for additional air changes.

The heating technologies are co-ordinated by a BMS installed by Control Tech Ltd. Nigel Hayes of the company says that the system is calibrated to select the most efficient technology, or combination of technologies to run the building at any given time. It is aided in this task by an onsite weather station which measures temperature, relative humidity, barometric pressure, rain intensity, wind speed and wind direction. In addition, indoor sensors measure everything from temperature to CO2 and total volatile organic compounds (TVOC) levels. All of these systems can be overridden for educational purposes, so that it is possible to select whichever technology is to be demonstrated. The system can also be used to co-ordinate the building’s electricity use, balancing the CHP and the PV system to prompt the most efficient use of power.

Control Tech also supplied a traffic light ventilation system – which may prove a critical way of protecting occupants from the risks of indoor air quality declining, given the potential for large variation in air change rates in naturally ventilated buildings. As long as air quality in the centre remains good, a green light is displayed. Once CO2 or TVOCs move above pre-programmed set points however, that green light switches to amber, while red is displayed if another set of thresholds is breached. Users then react to these signals by adjusting ventilation levels to improve air quality.

A similar system operates for gas, electricity and water use. If these move above baseline set points, the traffic lights prompt a change in user behaviour.

Ballymun’s Rediscovery Centre has been open now for a little over six months. Projections suggest that upwards of 10,000 visitors will pass through its doors before year end. As ABK’s Robert Davys points out, the main aim of the centre is to effect positive behavioural change. “Every aspect of the building is being used as an educational opportunity.”

Building services, construction materials and pipework have been left exposed and are labelled so that visitors know exactly what they’re looking at. There are viewing panels into plant room, workshops and out onto the roof.

The project shows exactly what can be achieved from a site that three years ago was a rundown eyesore. It’s fitting too that the site of the country’s first ever district heating system has been repurposed to create an exemplar of sustainable construction.

1 A panel of internal plasterboard intentionally removed to reveal the internal Hempcrete, a combination of hemp and lime that provides both insulation and structural function; 2 The derelict boiler house prior to the refurbishment; 3 Timber  shuttering system for construction of the Hempcrete walls; 4 The timber frame wall sections were insulated with 150mm of reclaimed sheeps wool.

Image gallery

• Facade sections Facade sections
• Facade sections Facade sections
• First floor First floor
• Ground floor plan Ground floor plan
• Site plan Site plan
• Water reuse and treatment Water reuse and treatment
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