Conor Walsh, of sustainable building firm Encon, says there’s one factor above all others that determines quality on site. Time. Time to plan, time to choose materials, time to build to the right specification.
“You’ve got to make sure that you’re using the right product in the right place, and that you’re not just relying on the local hardware store. Take the time to look around, to see what’s out there, what’s the best way of achieving the standard.”
This is why, when Walsh is looking for products, he casts a wide net, and buys in from all over the country.
“A good plan is key from the start,” he says. ”You have to give yourself enough time to choose your materials, because if you leave it ‘til the last minute, you’ll take anything.”
Good materials were key to the refurbishment and extension of his own home in Waterford City. The retrofitted bungalow approaches the Enerphit standard by taking a fabric first approach and combining a range of building methods, including cavity wall, insulated concrete formwork (ICF) and external wall insulation (EWI).
Walsh had been looking for a site to build a home for himself and his family, but rather than opt for a new build, he decided instead to renovate and substantially extend a sixties-era cavity wall bungalow on a site at Leoville in Waterford City. Conor’s young son is a wheelchair user, and for that reason, it was important that the house remain a bungalow. But because the existing house had such a poor energy profile and was not designed with wheelchair use in mind, much of it was unusable.
“The orientation of the existing house was right, so we kept the bedrooms on the north and east elevations, while most of the living spaces in the house were south and south west facing. For that reason, we used 90% of the original foundations and retained about 20% of the original walls.”
Passive principals always favour a compact footprint in order to minimise heat loss form factor. This is the ratio of heat loss surface area to the usable floor area. Typically, form factors lie between 2 and 4, with 2.5 considered optimum. At Leoville, Conor Walsh achieved a ratio of 2.72.
This was no small achievement given the size of the house (340m2) and the fact that everything was on one floor. Walsh explains that while his architect advised an L-shaped footprint, he felt that this would drive the form factor too high. Moreover, he liked the solid, square aesthetic of period homes, and wanted to achieve something like that in his house. The problem was that building a large square house would have left the central section without natural light. The solution was an atrium at the centre, with a large glazed section built into the roof.
“We were very conscious of the fact that because it was a bungalow, there would be quite a large floor area. That’s why we concentrated on getting it square and compact, keeping it nice and tight…And that lead to the design of the atrium.”
Walsh chose insulated concrete formwork (ICF) as his build method for the new part of the house. Quality was the driver here. In aiming for passive standards, two elements of the build are critical; air tightness and the elimination of thermal bridging.
“When it comes to thermal bridging,” says Walsh, “your main problem is always going to be how each layer – floor, wall and roof – connect together. ICF is an amazing product, the way the floor slab, the floor insulation and the wall insulation connect together seamlessly. We were able to achieve an excellent thermal bridge free detail there.”
The other advantage of ICF is air tightness. Because of the density of the concrete mix, ICF walls are naturally airtight.
In order to further beef up the thermal profile of the wall, Walsh also decided to add external wall insulation to both the ICF and the cavity walls of the existing house. Given the varying thicknesses of these separate build-ups, the design and build team had to take care to ensure that the finished surface remained flush between the two, and that the insulation ran in one continuous layer.
Ultimately, the house achieved an ACH of 1.1, just outside the Enerphit standard, but still a very good result, and a vast improvement on the 7.4 ACH measured in the old house.
Again, Walsh returns to that same principal – giving yourself the time to achieve the standards. “If you rush a job, you tend to compromise on quality, so you’ve got to make sure you price for what you’re going to do. If you under price, you’re going to end up compromising on quality. Price it right and do it right.”
He notes too that keeping his own skills up to date is vital. To that end, he attends regular trade shows and uses the internet to keep tabs on new products and processes as they come on stream. Working with the same crew through successive projects has also been essential to maintaining onsite quality. Walsh ensures that his team’s skills are kept up to date through a combination of ongoing experience and regular training sessions at different locations around the country.
Once a project gets onsite, monitoring becomes a central plank of his approach to quality.
“We use photographs to keep everything recorded. If I can’t be onsite for a particular day, then I’ll ask my site foreman to make sure that he has photographic evidence of the stage that he’s working on, and I check to make sure that the product is being installed to the spec.”
To get sufficient light and to achieve the right aesthetic, Walsh upped the glazing spec in the house. All told, it features 80m2 of glass, against a floor area of 340m2. At nearly 24%, that’s a higher glazing ratio than you would normally expect in a passive house. It’s no surprise therefore that when the house was modelled on the passive house software, PHPP, an overheating risk of 10% was identified. One of the big culprits here was the central atrium.
“It was going to get a little bit too much solar gain in the summer,” Walsh explains. “that’s why we put opening vents in the atrium so that it acts as a natural chimney and gives us a cooling effect. We also put an extract ventilation unit in the hall to try to remove some of the warmed air.”
Internal blinds have also been installed to combat any overheating issues, and Walsh reports that throughout last summer– although it wasn’t particularly hot – the house never overheated. If problems do arise, the plan is to install a cooling unit in the MVHR system, then mitigate the increased power load with a solar PV array on south-facing roof.
Walsh, together with energy consultants Integrated Energy, explored a range of heating options before eventually deciding on a traditional approach.
“We didn’t really feel the need to overspend on a heating system,” says Walsh. “We were aiming for close to passive standard and put a lot of money into the building fabric, which in turn requires a minimal heat system, so we just went with a standard oil boiler and radiators throughout.”
In addition to the extensive glazing, Walsh’s design included a raised plinth, and he also installed solid granite cills on the windows, to help give the house that period look and feel. These, he admits were a tricky install, since care had to be taken to ensure that there were no thermal bridging issues.
“Generally, passive houses can be quite minimal design, quite simplistic,” he says, “but I feel we pushed the boundaries here a little, and achieved an energy efficient house with some beautiful design details.”