Big savings delivered by deep retrofit in Wicklow
SIMON Maher says that when he and his wife, Siobhan Kennedy, moved into their house in Glenealy, Co Wicklow, they found it very difficult to heat. “Gas was costing us an astonishing amount of money,” he says. “There was only single glazing at the time, so the first thing we did after we bought the house was to put in double glazing, and we also installed external insulation.”
The couple never intended to stop there, however. They knew that down the line, they’d need to extend the house for their growing family, and that when they did, there would be an opportunity to improve the energy profile and comfort of their home still further.
“Myself and my wife are quite passionate about the whole area of sustainability,” says Maher. “We obviously wanted to reduce our financial outgoings, but we were also aware of our impact on the environment. We wanted to reduce our footprint as much as possible, while also giving us more space for our family to live in.”
Because the existing windows were relatively new, and the old part of the house had already been externally insulated, the decision was taken to leave that section of the building largely untouched, and to concentrate measures in the extension.
A hallway introduced at the centre of the house was designed to serve as a link between new and old sections. The design itself made extensive use of fold architecture, a familiar feature in contemporary buildings where a continuous material is used to create both wall and roof. The entrance canopy has a pressed metal roof that begins horizontally, then drops down vertically, creating a kind of baseball glove, which catches the person as they approach the house.
It looks great, but from a thermal point of view, this feature had the potential to introduce a substantial thermal bridge. Thermal bridges are effectively weak spots in the building envelope, which reduce the thermal efficiency of the house and open up a risk of condensation, mould growth and other associated problems. In a passive new build, thermal bridges can be detailed away by creating a continuous insulation layer. With deep retrofits, that isn’t as easy to achieve. Careful detailing and the use of materials which do not conduct the heat got over this particular issue.
Creating a continuous, flush external finish so that the link between old and new is invisible is another challenge on retrofits. The walls of the existing house had been finished with external insulation, while the extension walls relied primarily on cavity insulation with a render finish. The design and build teams then used partitions to swallow up any differences in depth, in order to deliver an even finish.
Ensuring an air-tight building envelope is an essential part of any major retrofit. This is all about keeping the warm air in and the cold air out. In Glenealy, the design team achieved air-tightness using an internal wet plaster finish, in combination with air-tightness membranes and tapes at windows and around junctions.
The much improved air-tightness profile meant that a controlled ventilation strategy was essential. The team chose a Paul Novus 300 MHRV system, with a heat recovery rate of 84pc.
The client opted to continue with gas central heating, replacing the 20-yearold boiler with a new, condensing unit, supported by a room-sealed solid fuel stove. After just over a year in the house, Simon reported that heating bills had dropped dramatically. Prior to the works, the household was spending between €1,800 and €2,000 annually on gas. Since moving back in, the bill has stayed below €850.
Another measure Maher and Kennedy took prior to the latest retrofit was the installation of a solar photovoltaic (PV) array on the roof. The installation was completed in time to take advantage of ESB Networks’ now discontinued support package for microgeneration. While those incentives have expired, the ESB will pay 0.9c per kilowatt hour for any unused power exported to the network.
The BER went from D3 in Jan 2011 to C3 in May 2014 (when the solar PVs were fitted to the roof ) to an A3 in December 2015 after the build was completed.
“Right now, it’s perfect,” says Maher. “We don’t have to heat the house at all. We’re getting around 22 degrees throughout the day and we supplement that with our wood-burning stove in the evening if it gets cooler.”