Seal of office

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Building type: Four-storey, 4,710 m2 office building
Method: Steel frame with celluloseinsulated timber panels
Location: Enniscorthy, Co. Wexford
Standard: Passive house classic
Embodied carbon: Meets RIAI 2030 Climate Challenge target

A landmark development on a prominent site just outside Enniscorthy in Co. Wexford has become Ireland’s first passive house certified office building. Built by longstanding passive house contractor Michael Bennett Group under a design and build contract, Senan House was designed by passive house architects MosArt.

With that combination of expertise behind it, this building was always going to be exceptionally high performing. It also represents an early benchmark in respect of embodied carbon for Irish office buildings.

“Ever climbed Croagh Patrick?”, architectural technologist Stephen Donoghue asks in response to a query about the challenges posed by the site. Enniscorthy is a hilly town.

Its new technology park – of which Senan House is the lead building – is cut into the side of a steep hill that runs down to the Wexford road and the river Slaney, which run parallel to each other for about five kilometers outside the town. During the early stages of the project, preparing a sloping site and getting levels right was very challenging, not least because of the unstable wet marl that comprises so much of the land in this part of the country. The payoff comes in a striking building with fantastic views. Senan House runs on a slightly cranked north-south axis, with views of the river valley to the west. You can see the town with its spires against the backdrop of the Blackstairs Mountains to the north while St. Senan’s Hospital – a distinctive Victorian building now converted into apartments – can be seen through the southern windows.

Art McCormack of MosArt explains that the reference building for this project was a successful tech incubation space called The Hatch Lab down the road in Gorey. Once brought on board by Michael Bennett, MosArt created a masterplan for the site, which included the construction of a sister building alongside Senan House. Wexford County Council, who plan a pedestrian and cycle bridge linking the town centre and the technology park, owned the site and supported the development through all its phases.

A variety of design options – including the possibility of creating a construction training centre – were explored before the team settled on a rational, flexible office building. The first plan ended at the third storey, but following input from Wexford County Council, it was decided to add a fourth, recessed, penthouse-style storey facing west to the river.

Further proof of the support of the local authority comes in the fact that it took just five weeks to get through planning.

“The steep site was one of the main design problems,” says Art McCormack. “So, we used the higher ground to the east to create a bridge and enter the building at the first floor level.”

In the original plan, the central bay which projects towards the river housed a multi-height atrium. The site was subsequently sold to a private company however, and, as McCormack puts it “they added insight into how the offices might be optimised.” Rentable floor space was expanded, and the atrium took on more modest dimensions.

McCormack explains the north-south alignment follows the contours of the site and makes sense in terms of road layout and how the building would be accessed via that aforementioned bridge linking the car park with the first floor.

The detailed design stage coincided with the pandemic and everything that went with it. A subcontractor was commissioned to provide the timber wall panels that the design team had settled on. Covid-related issues forced that contractor out of the project in mid 2020 however, and finding a replacement proved challenging. During this period, the design team almost decided on a cross laminated timber (CLT) construction. This is the process of using bonded layers of solid wood panels for floor, roof and wall elements, thereby achieving carbon savings that are vastly superior to concrete and steel.

In the end however, the financials didn’t add up, and PYC Construction stepped into the breach with their I-beam system. They built and supplied the factory-fabricated timber panel I-joist system that was used on the build – a low embodied carbon system designed to be airtight, breathable and windtight. The 240 mm wide panels comprise Propassiv boards on the inside taped at edges, I-beams fully filled with close to roughly 67 kg/m3 of Warmcel cellulose, Meditevent board and Pro Clima Fronta Wa, taped for wind tightness. While the panels came pre-taped, they were taped together for airtightness, and taped to the concrete slab and roof.

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Stephen Donoghue lists the advantages of this build approach. “There’s less mess, it’s cleaner and safer, and the panels go up faster, plus you get better quality. And you don’t need scaffolding. There was no scaffolding erected on this building.”

In order to avoid thermal bridging where the external walls meet the structure, the panels were hung from the steel beams. This was one of several strategies deployed to ensure an unbroken thermal envelope. Though the bridge at the main entrance looks as though it’s connected to the building, it is structurally separate, and actually ends 5 mm from the wall. On the top floor, a 10 mm load-bearing insulation was used to separate the steel base plate which supports the roof canopy from the insulation below, and rainwater downpipes were wrapped with foil-backed insulation from roof to ground floor.

Windows, curtain walling and external doors are Passive House Institute certified. The windows have thermally broken aluminium frames, which were manufactured locally by Reynaers Aluminium. Unusually in an office space, all units are triple glazed, and glazing covers 23 per cent of the structure. At 1.34, the building has an excellent heat loss form factor.

According to the PHPP, there is zero risk that the air temperature will exceed 25 degrees over the course of the year. In the absence of brise soleil, overheating risks are mitigated by glass with three separate G values, ranging from 42.7 per cent down to 27.8 per cent.

Art McCormack notes that there was a particular overheating risk in an office high in the central bay, which projects east but also has exposure to the southern sun. Again, that risk was dealt with using glazing with a very low G value.

Doubts about the airtightness strategy planned for the raised mono-pitch steel panel roof prompted the build team to construct a mock-up onsite, and test its airtightness, just to see if it would work. It didn’t. The dovetailed system failed, so all the panel joints and roof-to-wall junctions were taped by airtightness contractor Aerzeal Ltd, with input from Joe Fitzgerald from Ecological Building Systems and Roman Sypura from Clioma House. The subsequent test confirmed an excellent score of 0.15 ACH at 50 Pa.

There is no oil or gas onsite – the office is fully electric. Integrated units from Nilan – two per floor – look after heating, cooling and ventilation. These units are connected to the Nilan Cloud system, a cloud-based management system which allows the facilities manager to remotely control the system as they wish, rather than going to individual control panels, and which enables remote servicing and maintenance. A large PV array supplements the power load. At one point, the plan was to mount the panels on the pitched roof, but the change to the roof spec as a result of airtightness issues prompted a rethink, and the panels – 119 in all – were relocated to the flat roofs.

The system was actually installed by the building’s first tenant – Pinergy Solar Electric. CEO Ronan Power explains the system generates an annual average power of just over 44,000 kWh, with peak power of just over 48,000 kWh.

“The install here was quite similar to those we’ve done with other corporate customers. Because this was a building still under construction rather than a retrofit, however, it was quite a complex lift and build, with a number of health and safety issues. So far, the generation appears to be excellent.”

The HVAC units have yet to operate. So far, things are really comfortable.

He expects the system to offset in the order of 20 per cent of the building’s total power demand. There is also an export connection under ESB Networks’ mini-generation connection process which effectively compensates users for any unused electricity that is exported to the grid.

Power says that he and his colleagues moved in last February. “We’ve our feet under the table at this point, and it’s great, we love it here. Senan is very aligned to our core values, in terms of sustainability, and it’s nice knowing we’re in a passive building.”

Though the company has not yet seen a full heating and cooling season, first impressions are very good.

“The building seems to be performing very well. Bear in mind, mine is a corner office, with two external windows. We’re monitoring humidity and CO2, and everything is staying within normal levels. There’s just ourselves – twenty-four people – and one other tenant so far. That’s not a huge load, and the HVAC units have yet to operate. So far however, things are really comfortable.”

And there’s no comparison with the company’s last office, he says, which was old, with all an old building’s flaws. It’s currently being retrofitted.

“Ours is a growing business, so this is ideal for us. We’ve got space to expand, and we signed a ten-year lease because we want to continue to stimulate employment here.”

• The steel frame structure; the thermal envelope takes shape with PYC Construction’s cellulose insulated, airtight panels and windows and steel battens and counter battens The steel frame structure; the thermal envelope takes shape with PYC Construction’s cellulose insulated, airtight panels and windows and steel battens and counter battens
• Heating comprises air-based heat distribution via two Nilan VPM 360 MVHR units per floor Heating comprises air-based heat distribution via two Nilan VPM 360 MVHR units per floor
• The steel frame structure; the thermal envelope takes shape with PYC Construction’s cellulose insulated, airtight panels and windows and steel battens and counter battens The steel frame structure; the thermal envelope takes shape with PYC Construction’s cellulose insulated, airtight panels and windows and steel battens and counter battens
• The steel frame structure; the thermal envelope takes shape with PYC Construction’s cellulose insulated, airtight panels and windows and steel battens and counter battens The steel frame structure; the thermal envelope takes shape with PYC Construction’s cellulose insulated, airtight panels and windows and steel battens and counter battens
• Airtightness tests were conducted on a mock-up of the roof system to catch and address leakage issues Airtightness tests were conducted on a mock-up of the roof system to catch and address leakage issues
• To obviate thermal bridging where the external walls meet the primary steel structure, the wall panels were hung by steel lugs from the steel beams To obviate thermal bridging where the external walls meet the primary steel structure, the wall panels were hung by steel lugs from the steel beams
• To obviate thermal bridging where the external walls meet the primary steel structure, the wall panels were hung by steel lugs from the steel beams To obviate thermal bridging where the external walls meet the primary steel structure, the wall panels were hung by steel lugs from the steel beams
• The windows have thermally broken aluminium frames, which were manufactured locally by Reynaers Aluminium The windows have thermally broken aluminium frames, which were manufactured locally by Reynaers Aluminium
• A 10mm thick Farrat TBK structural load-bearing insulation was used to separate the steel base plate from the insulation within the structure A 10mm thick Farrat TBK structural load-bearing insulation was used to separate the steel base plate from the insulation within the structure
• Precaution was taken to wrap rainwater down pipes with foil-backed insulation from roof to ground floor; Precaution was taken to wrap rainwater down pipes with foil-backed insulation from roof to ground floor;
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Embodied carbon

A cradle-to-grave embodied carbon calculation was done by Ciaran Flanagan of MosArt using One Click LCA.

The scope included all the big ticket items within the building itself - the foundations, superstructure, thermal envelope, PV array and heat pump and ventilation system – but did not include the external works, including the car parking area, which would likely have added a significant amount. The building fit out was excluded, as were the ducts, pipes and cables for buildings services.

In many cases punitive default data from One Click was used, in the absence of Environmental Product Declarations, most notably in the case of the three largest sources of the building’s embodied carbon: the structural steel frame, concrete, and PV array, which respectively contributed 1,200 tonnes, 371 tonnes and 180 tonnes of CO2e to the building’s cradle-to-grave total of 2,357 tonnes – or 484 kg CO2e/m2 of gross internal area, comfortably inside the RIAI 2030 Climate Challenge target for offices of 750 kg CO2e/m2, albeit with omissions from the scope including a potentially large total for external works.

Image gallery

• Building elevations Building elevations
• Downpipe detail Downpipe detail
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