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Ultra low-energy cottage in Stepaside

It’s always easier to rebuild a home to an ultra low-energy specification than to retrofit a Victorian-era dwelling to the same standard, so when the building in question turned out to be beyond saving, it gave the owners the chance to do just that.

In 2010 Nick Burrett and Orla O’Shea bought a Victorian cottage in Stepaside, Co Dubin with the intention of renovating it a year or so down the line.

“When we bought it, it was in a terrible condition anyway, we knew we had to do work on it,” Nick says. Both the roof and back wall were in danger of collapse.

They planned to renovate the cottage and build a large extension in one go. Architect Hugh Geoghegan’s practice Archi-i was appointed to design the project, with Dublin-based Bourke Builders as contractor.

“The build quality was terrible – it allowed for massive heat losses and rodent infestation,” Hugh says. And the team weren’t long on site when they got a big shock. “We were three weeks into work on site when it became clear that the fabric of the existing dwelling could not be salvaged.”

The existing structure was infected with dry rot and mould, and there was substantial water damage. Pipes had frozen and cracked while Nick and Orla were away, soaking the roof timbers. The level of damage caused by water ingress only become obvious once the builders started pulling apart the old cottage.

They decided to knock the original structure and build a new cottage instead. “There was a lot of on-the-hoof design, it was quite challenging,” says Hugh.

While it provided them with the opportunity to build to Passive House standard, they had more difficulty getting a mortgage than they expected. They put plans for the extension on hold and opted to finance the rebuilding of the cottage out of their own cash reserves.

The site is also on a granite hill, and the team worried they would end up having to excavate a big chunk of granite — potentially another big cost. But they wouldn’t know until the diggers were on site. Pushing the extension back and focusing on the cottage first would help to keep those groundwork costs under control should they arise.

The old cottage was knocked, and work began on its replacement. The walls of the new cottage were built with concrete block, externally insulated with EPS and finished with mineral render.

Bourke Builders have worked on several low-energy and Passive House builds, most notably the Wynberg Park EnerPHit project in 2012 with architect Joseph Little. Writing in Passive House Plus magazine about that project, Little said that it was a learning curve for many people involved, including Bourke Builders, in terms of getting the airtightness right. The builders had started early on the insulation work but needed to pause and undertake some corrective actions to ensure that the first airtightness tests were successful before finishing the job, as any problems that emerged later would be more difficult to fix.

“If it’s not reached at this stage, when the layers of buildups and number of penetrations are relatively few and easily accessed, it never will be,” he said.

A few more tests were necessary before Bourke Builders could proceed to the first fix, but they paid for the additional tests. “Their commitment to getting it right was central to the team’s achievement of EnerPHit certification,” said Little.

On the Stepside house, the airtight layer is provided by plaster on the block walls, and by Pro Clima membranes and tapes in the roof. The final airtightness test, performed by Gavin O Sé of Greenbuild, produced a result of 1.95 air changes per hour. Greenbuild also assessed the house under the Code for Sustainable Homes, and it came in at level four.

There’s no whole-house ventilation system, only standalone extract vents in individual rooms, but the house has been built to take HRV ducting which will be installed when work on the extension begins — though Nick now says he wishes they’d installed it up front.

Ironically, the team ended up finding no solid granite. But Nick thinks that ultimately, not being able to do the whole extension at the same time was a blessing in disguise. “I think if we’d have done it all in one go like we were going to, we’d have had a big problem financing it in the end.”

Since they’ve moved in (2013), Nick and Orla have been impressed with how the house has performed over winter months. “There’s very little temperature drop throughout the night so it’s quite comfortable to just sit around in the early hours of morning, which we have been doing because we have a young baby. Heat retention has been very good.”

“I realised that it’s better to invest the money in insulation and doing it to a high specification, because it saves a fortune in the long run really.”

They’ve only used up about a quarter of their 600 litre oil tank since October, whereas previously they’d have gone through a 1,000 litre tank every six to eight weeks.

“We’ve rebuilt a cottage and have an understanding of the materials used in the construction and their performance,” Nick says. “We have an energy efficient home and a much clearer idea of how to improve things for the construction of the larger extension.”

The extension will be almost four times the size of the cottage, so the energy efficiency goals will be higher there.

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