Ballymore scheme brings low-cost comfort to private market

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Development type: 30-unit residential development comprising three-storey semi-detached houses and two terraced blocks of three units each
Method: Timber frame construction with atomised airtight and air source heat pumps
Location: Portmarnock, Co. Dublin
Standard: Passive house classic
Heating costs: €214/year. (Calculated annual space heating costs. See In detail panel for more information).

When Charlie Conlan describes Ballymore's Drumnigh Oaks development in Portmarnock as "a boutique compared to the usual 200 units," he's being modest. The 30-home project represents something more significant than its small scale suggests: a serious attempt by a major developer to demonstrate that passive house standards can work commercially in the mainstream housing market.

The development, which completed construction recently, has become a testing ground for sustainable construction techniques that Conlan, Ballymore's sustainability designer, hopes will eventually become standard practice across the company's portfolio. But the project has also exposed fundamental flaws in how Ireland measures and values energy efficiency in homes — and how regulatory barriers may be inadvertently blocking sustainable innovation.

"We're trying to raise the bar across the board and onboard new technologies, practices, software, and so on," Conlan said. "That's part of the innovation team's mandate, and once it graduates, it will become standard practice."

The project's origins reveal something important about how sustainability innovations can emerge in the commercial development sector. Don McMahon, Ballymore's residential construction director, explains that designing to passive house standard wasn't part of the original vision.

"We went in for planning on this development, but the concept of passive house wasn't initially considered," McMahon said. "After the grant of planning, Charles was one of the main drivers, along with Patrick, our MD."

This approach – effectively a design retrofit, with detail design having to work around the restrictions imposed by the approved form, orientation and layout – certainly created challenges. Rather than designing from scratch for optimal passive house performance, the team had to adapt existing plans to meet the exacting standards.

"If you started from a blank page, you would design something that would be fundamentally easier to construct," he said.

A quick glance at the homes reveals the extent of the challenge. Bay windows, lean-tos, parapets and a mix of roof types posed a number of challenges in terms of detailing airtightness and thermal bridging.

But the strategic thinking behind choosing this particular project was clear, McMahon said. "If you look at the scale at which we're delivering houses, it's interesting to see if they can be delivered as passive houses at scale. We have developments that range from 125 to 400 homes. This was a development of 30, so it was ideal in terms of ticking the boxes for a test".

Peter McCaughey, managing director at IJM Timber Frame, puts the scale in perspective. "This was a pilot for Ballymore. We could have picked something easier to pilot. We're producing about 1,500 units this year, so in those terms, it's small, but it's a big step for developments. I think great vision is being shown," he said.

Technical innovation under pressure

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The Portmarnock site presented unique challenges for a passive house development. The 30 units comprise mainly three-storey semi-detached houses alongside two terraced blocks of three units each. The timber frame construction required careful attention to thermal bridging, particularly where steel portal frames were used for rear lean-to extensions.

"Insulation was packed into the steel sections," Conlan explained, describing how thermal bridges were addressed.

McCaughey confirms that structural steel remains problematic: "Structural steel is normally problematic, causing a cold bridge for a start, which we will try to mitigate, of course."

The building fabric specification included a 150 mm concrete slab on a 250 mm Unilin Xtroliner XT/UF PIR insulation layer, with polythene-bound thermal blocks to form the rising walls -- combined with 35 mm of PIR to the upstand, underneath the IJM timber frame wall. But it was airtightness that proved to be the most critical factor.

"The fact is that airtightness for us was probably the largest factor in achieving the passive certification," McMahon said. "The timber frame lent itself to doing that."

McCaughey said a factory-controlled approach provides advantages: "A lot of the airtightness is dealt with in the factory, but then it's the joints. The biggest issues, I would say, are things like the base that the timber frame is going onto: Is it adequately level? Is it square?"

• 250 mm of Unlin Xtroliner XT UF insulation 250 mm of Unlin Xtroliner XT UF insulation
• MVHR ductwork and services in metal web joist MVHR ductwork and services in metal web joist
• The MVHR system is supplemented by a Daikin Altherma air source heat pump in each house, including an outdoor unit and indoor unit The MVHR system is supplemented by a Daikin Altherma air source heat pump in each house, including an outdoor unit and indoor unit
• Radon barrier on sand blinding and rising walls – consisting of two courses of Kilsaran K-Block Thermal Lightweight blocks; As passive house certification requires evidence to be provided demonstrating the designed insulation levels have been achieved, measurements showing insulation thickness are common in passive house projects Radon barrier on sand blinding and rising walls – consisting of two courses of Kilsaran K-Block Thermal Lightweight blocks; As passive house certification requires evidence to be provided demonstrating the designed insulation levels have been achieved, measurements showing insulation thickness are common in passive house projects
• 40 mm insulation to upstand of thermal block rising walls 40 mm insulation to upstand of thermal block rising walls
• Mineral wool insulation fitted into steel beam Mineral wool insulation fitted into steel beam
• A void in slab to accommodate extra insulation at the base of the portal frame A void in slab to accommodate extra insulation at the base of the portal frame
• Steel purlins were a structural element which posed a thermal bridging issue, and were wrapped in PIR insulation Steel purlins were a structural element which posed a thermal bridging issue, and were wrapped in PIR insulation
• Steel purlins were a structural element which posed a thermal bridging issue, and were wrapped in PIR insulation Steel purlins were a structural element which posed a thermal bridging issue, and were wrapped in PIR insulation
• Airtightness taping to Fakro roof window; Airtightness taping to Fakro roof window;
•  

Atomised airtightness

Although most of the heavy lifting on airtightness was done in the factory, the challenges posed by the complexities of design of these homes – bay windows, parapets, lean-tos and multiple roof types made hitting the passive house target of 0.6 air changes per hour at 50 Pascals particularly challenging – until Ballymore came across an innovation to get them over the line. "We came across an atomiser that puts a product into the atmosphere when the house is pressurised, and it migrates to weaknesses in the membrane," McMahon explained.

That problem-solving product is AeroBarrier, an airtightness system developed in North America and now gaining a foothold in the UK and Ireland, which was introduced to Ballymore by passive house consultants Mosart.

The system, represented on this side of the Atlantic by sister companies Aeroseal UK and Aeroseal Ireland, works by introducing a fine mist of water-based acrylic sealant into a pressurised building.

The system pressurises the building and releases a fine mist of water-based sealant, which is drawn to gaps and forms a durable film, sealing cracks from visible to pinhole size. Progress is monitored in real time and stops automatically once the target airtightness is reached. Greenguard Gold certified, AeroBarrier has been tested worldwide and significantly improved airtightness on the project, helping the homes meet the passive house target of 0.6 air changes per hour at 50 Pascals.

While Ballymore had already achieved low air leakage rates with the IJM system, the effects of adding AeroBarrier brought them over the line in terms of the passive house target of 0.6 air changes per hour at 50 pascals. "Our results were 0.7 or 0.8. After 45 minutes, we were at 0.1," McMahon said.

The heating strategy relies primarily on retention of heat – first through high performance building fabric, and second through a Vent Axia Sentinel Econiq mechanical ventilation with heat recovery (MVHR) system, which recovers heat from warm, stale air exhausted from bathrooms and kitchens and passes it onto incoming fresh air. This is supplemented by a Daikin Altherma air source heat pump in each house, which distributes heat via radiators and makes hot water. "Very little heat is needed outside of the MVHR," Conlan said.

The rating system disconnect

However, this highlights a critical disconnect between technical performance and market recognition. Ireland's Building Energy Rating (BER) system, which homeowners use to assess energy efficiency, fails to capture the true benefits of passive house design – in part because it enables homes to achieve seemingly excellent scores for homes which fail to achieve anything close to the kinds of comfort levels baked into the passive house standard.

The energy model behind BERs assumes that the living space in a home – which typically makes up circa 20 per cent of the total floor area – is heated to 21C, with the remainder of the home heated to 18C. This translates to an average of 18.6C. What’s more the home is only assumed to be heated to these levels for eight hours per day. During the 16 other unheated hours per day, the temperatures can drop significantly.

One hypothetical NZEB-compliant new home analysed by Wain Morehead Architects say the unheated hours dropping to down to less than 15.6C, and a 24 hour average of just 16.5C.

The passive house standard, on the other hand, assumes a far higher comfort level: a whole house average of 20C, 24 hours a day, seven days a week.

While passive houses have been shown to perform in line with the standard’s ultra-low space heating energy use target, the same cannot be said for BERs. A 2021 study found that homes with higher BER scores (meaning As and Bs) used on average of 39 to 54 per cent more energy more energy for heating, hot water, ventilation and lighting than calculated.

"The BER is the only thing that homeowners are aware of," Conlan said. "But it's not a good tool for measuring performance. A passive house is far less energy intensive than a normal house, but they could both be [classified as] A2."

The danger, he said, is that this can create a market dynamic where genuine energy efficiency improvements aren't recognised by the system buyers rely on. "Our houses could have got an A1 if they had solar panels, as could a lot of other houses, but ours are a lot more energy efficient, whereas the other one could be leaking energy," Conlan observed.

McCaughey said that consumer demand for high-performance buildings is limited by upfront cost considerations.

"The bottom line is that regulation will drive the change. Public demand or need is very difficult to create because there's always an added cost, and when that is built into the cost of regulation, everyone across the board will apply that regulation.

"When you look at that price point, this isn't going to cost you anything to run. It's a bit like electric cars: electric cars are a no-brainer, but people will consider the upfront cost."

Market momentum building

We're confident that we can do any typology to passive house; it's just a matter of getting the recipe right.

Despite these market challenges, the performance benefits are substantial. The homes achieve dramatic improvements in air quality alongside significant energy savings. "The air quality benefits are dramatic," Conlan said, referring to the continuous fresh air supply provided by MVHR systems.

More significantly, the project appears to be influencing broader market behaviour. McMahon notes that "given the recent planning changes in Dublin, a number of developers are trying a passive scheme for their apartment structures."

The project's broader significance lies in its role as a learning exercise for Ballymore's innovation team, though.

"When we're doing these pockets of innovation, we are trying to learn," Conlan said.

The collaboration with IJM has also been systematic: "Ballymore brought Mosart down to the factory. We're due to do another review of the manufacturing process to see what we can try to build in to make achieving the airtightness better and easier," McCaughey said.

McMahon said that the development shows that technical challenges are surmountable: “The design, mechanical and electrical, the envelope — that can all be done." The team worked with O'Mahony Pike architects to solve the design constraints imposed by retrofitting passive house standards to existing plans.

"We haven't done apartments to passive standard yet," Conlan said. "Houses will have more nuance than apartments, whereas apartments will typically have stricter cost constraints. But we're confident that we can do any typology; it's just a matter of getting the recipe right."

Seen this way, Drumnigh Oaks experiment raises some important questions about Ireland's approach to sustainable development. While the technical achievements are significant, the project highlights how regulatory frameworks and market mechanisms may be hindering rather than supporting genuine sustainability improvements.

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