This story was originally published in Passive House Plus magazine, and is reprinted with permission as well as updated with new comments from builder David Nally of Michael Nally and Sons (5/4/2016). Exterior photos by Kelvin Gillmor
This certified passive house in Galway isn’t a new build, it’s a retrofit. And it’s the first retrofit to achieve passive house certification in Ireland. It was also the first passive house project for the builder, Michael Nally & Sons, but they were determined to get it right.
A new retrofit project in Galway has shown just how far the retrofit of a typical Irish home can go, by bringing a 1960s semi-detached house up to the full passive house standard. The house in Salthill is home to Ciaran Ryan and Mary Hodkinson, who had been living west of Galway City in Furbo, where they had built an energy efficient home in the 1990s.
But they were keen to move to the city, and wanted a comfortable home they would never have to refurbish again. “We’re not going to move again after this. We want it to be really cheap to run, we want it to be warm and dry,” Ciaran says. They planned to buy an existing house and retrofit to a high standard.
They found a semi-d for sale in Forster Park, Salthill for the right price — and with the front facade facing due south. “It’s got a nice compact plan, which is very important. The nearer to a cube you can get the house, the easier it is to satisfy the requirements of passive house,” says project architect Simon McGuinness. This was crucial, because the budget wouldn’t stretch to making up for a lack of solar gain with, say, extra insulation.
The job came with a contractor in tow. Michael Nally & Sons had already built an extension to Ciaran and Mary’s house in Furbo, and the couple had been impressed with their workmanship.
Dave Nally says that it is team work and experience working together that allows them to bring an attitude of good workmanship and quality building to each project.
“It’s about team work. We are a family business with three generations of our family working together. Along with our family, our sub-contractors have been working together for numerous years over many projects; this allows our work to be of a consistent high quality standard. All sub-contractors who work on our projects know the quality of work that is expected on site, and this has this has enabled us to build a team that learns from each project.”
At the outset, McGuiness didn’t think it would be possible to achieve full passive house certification. The airtightness target of 0.6 air changes per hour (ACH), he felt, would simply be too onerous. “I didn’t think that was possible in a retrofit, because there was no record of anyone having done it,” he says. He did, however, guarantee the house would get under 1.0 air changes per hour, the Enerphit standard for retrofit. McGuinness also produced an extremely detailed set of drawings for the builders.
Airtightness tapes and membranes were fitted to windows and doors, then taped to the walls on installation before being wet plastered over to ensure a total seal
When it came to insulating the building fabric, external insulation was the only real option for the walls. Dry lining internally would have sacrificed too much floor space, and would have risked causing condensation behind the insulation. McGuinness specified an external mineral wool system from Weber, which is breathable and capable of draining moisture away. The flexibility of the material also meant it could be fixed tightly against the pebble-dashed house without plastering first.
The existing cavity wall was also insulated with platinum polystyrene bead. Meanwhile the concrete roof tiles were removed, and the roof insulated with Rockwool between and above the ceiling joists. A small porch extension was built with externally-insulated Quinn-Lite block, and Munster Joinery’s passive-certified Future Proof PassiV PVC windows and doors were installed throughout the house.
As you might expect with a passive house retrofit, airtightness was the biggest challenge. During the design stage, McGuinness drew the airtight layer in blue on all plans, sections and details. Photos were included in the tender demonstrating how to sequence airtightness works. When the builders were on site later, they would upload photos to Instagram for McGuinness to review workmanship remotely.
The airtightness strategy was guided by five principles: a complete wet-plaster finish from floor-to-roof on the inside of the walls, no chased services on the external walls, an airtight membrane under the first floor ceiling, passive house certified windows and doors taped to walls under the wet plaster, and a total removal of the chimney down to the foundations.
All the internal walls were cut back, and skirting boards removed, to ensure total coverage of plaster on the inner face of the external walls. Nally & Sons decided to remove all the internal partitions upstairs, which made it much easier to fit the airtight membrane above.
“Taking the responsibility for the air-tightness ourselves on this project,” says Nally, “ensured that we would achieve the best results possible. Throughout the project we did seven preliminary air-tightness tests to make sure everything was to the required level and nothing was missed. Multiple tests allowed us to address any unexpected impacts on the air-tightness.”
“Originally, the external walls were not scheduled to be re-plastered internally. But when we removed the existing wallpaper from the building, it was no longer airtight, as the wallpaper itself was sealing up some hairline cracks. As the old walls were posing a big challenge when it came to air-tightness, the decision was made to re-plaster these walls. It was the team’s first time on this type of project, and we were very conscious that we wanted to make sure everything was done right to meet the required air-tightness result.”
“Nally’s had never built to the passive standard before but were quick to learn…and quickly got to grips with the specification,” McGuinness says.
Nally points out that this project was a turning point for his team. “All of our projects are completed to a high standard; our team works closely with our sub-contractors to achieve quality throughout the project. At the start of this project we went to Ecological Building Systems which upskilled us on air-tightness, cold bridging and insulation. We also held air-tightness training on site for all sub-contractors to ensure the importance of the air-tightness layer not being breached. We also have lunch box talks on site and an annual training plan in place.”
“This project was a turning point for us towards the benefits of low- energy construction. We used this opportunity to up-skill our team and to better understand the main factors in improving cold bridging and air-tightness and the advantages of low- energy construction. This project now informs all of our other projects.”
PHPP, the passive house software, told McGuinness that if the team got the airtightness down from 1.0 to under 0.5 ACH — not as easy a feat as it might sound — the house’s space heating demand would drop from 19 to 15kWh/m2/yr, low enough for full passive house certification. This focused minds on site. “I knew the difference was going to come down to airtightness,” he says.
Ultimately, all the detailed drawings and photos paid off. “We only did one blower-door test and we got 0.37 air changes per hour,” McGuinness says. “So on that day we all had a pint.”
Ciaran and Mary have been living in the house now for over a year. “There’s been no space heating on, probably since the middle of February,” Ciaran Ryan says. (Note: This case study was originally published in Nov 2015.)
“We were almost looking forward to the cold snaps, just to see how does the house behave.” His verdict? “It’s just spectacular. Everything is a constant temperature. You get up to go to the loo in the middle of the night and the hallway is the same temperature as the bedroom, and the bathroom is the same.” One of the biggest challenges when they moved in was finding a duvet thin enough to not overheat under.
“You come in at any stage, and you don’t have to worry about getting warm, or putting the heat on, or putting on a coat for the first fifteen minutes until the house heats up,” he says.
The house received full passive house certification earlier this year, making it the first such retrofit in Ireland. Nally feels that this project can be an inspiration for other low-energy retrofit projects. “We now have the knowledge and skills to improve energy performance on our current projects. Now that there is a benchmark for low energy retrofit, it will be good to see more projects of that type – we now know it can be done.”