Smart Series: the CLT house
French architect Julie Villard has built a quiet, airy, compact smart home above a noisy, smelly port.
The elegant styling of this European-inspired smart house hides a lot of secrets
The elegant, clean roofline of architect Julie Villard's smart house has a secret. It's out in plain sight, but a lot of people don't spot it. “If you open an architectural book you'll never see gutters or downpipes,” says Julie. “I wanted a detail for the roof and the wall where you don't see them.”
Instead, the water falls over the edge of the roof and runs down the side of the steel cladding.
“The building code requires you to collect the water coming from the roof. You can collect it at the bottom of the roof or you can collect it at the bottom of the wall with a surface drain and that's what we've got here. It's my architectural feature, my French touch.”
It's one clever little detail of this very smart house.
French-born Julie is the eco design advisor for the Christchurch City Council. People get a free, two-hour consultation with Julie, who shows them how to make their new build, renovation or retrofit, warmer, dryer and more efficient.
She is appalled at how New Zealand homes, even new ones, are cold and inefficient. That was a problem when she
and partner Edward wanted to buy a house.
“We couldn't find anything we liked to my European standards regarding energy efficiency and comfort. We went, ‘ok, we have to build'. Halfway through the process, I started my new role at the council... and I decided to use the house as a tool to show people you can achieve a good and efficient home.
“By building a house following the (eco design) principles, I'm walking the walk, and at the same time showing people you don't necessarily need a big house.
“It's about needs versus wants. It's about conscious choices. I prefer to build a two-bedroom house with a mezzanine – people can sleep there if we have guests – instead of having a third bedroom that we're never going to use.”
The couple used the money they didn't spend on size to pay for smarter options. For example, the underfloor central heating system heats the whole house and doesn't cost a lot to run. The system was sized to the house with a room-by-room thermal analysis. Total cost: $13,000.
“We had quite high expectations of being warm. Ideally, reducing the size of the house allowed us to achieve the outcome we wanted.”
The brief
The site Edward and Julie bought is just 10.5m wide by 50m long, meaning the house had to be small and narrow.
“I grew up in France, with a family of four in 130m²,” says Julie. “I knew I didn't need a lot of square metres for a comfortable-feeling home. It was a different story for my partner. Eddy comes from a bigger family, living in larger houses. At the beginning, he was triggered by the size of the house, only 53m² per level and 4.5m wide. He realises now, it's actually not a small house... the walls on the first floor are 3m high and balance the long, narrow volume.”
Julie wanted to use cross laminated timber (CLT), a natural wood product, as the structure of the house. It meant she could design a warm, energy-efficient building because she could create a continuous thermal envelope, with no thermal bridges (see page 30).
“In Europe that's standard,” says Julie. “We insulate houses from the outside and CLT helped me to do that.”
Another important aspect was using products that didn't require finishing.
“(CLT) is a natural, finished product, and we like the timber look. The concrete floor is also natural, no aggregate visible, so it looks like the concrete floor in a warehouse.
“It's just the materials, no cheating, no hiding, this is what they are naturally.”
"It's about conscious choices... you don't need a big house."
"The port is really noisy... the windows are designed to have a decrease of 36db... so it's very quiet inside." (Source: Beacon Pathway). Julie Villard, architect
Unlike common insulation batts, wood fibre insulation is self-supporting and doesn't need to sit inside a timber structure. Insulation that sits in walls and roofs can leave around a third of a house uninsulated due to gaps and light fittings. A gap the size of a finger can reduce the efficiency of 1m ² of insulation by 30 percent
The design
The hardest thing for an architect is to make a layout functional and simple. Julie's inspiration was Lyttelton's new Te Ana marina, and the local boat sheds.
The home steps down a hill. The living area is at street level; bedrooms and a bathroom are down a flight of stairs, hidden behind the kitchen bench.
“Each level is only 53m², and because of the roof pitch and high walls, the house feels way bigger; and the simple layout helps quite a bit.”
The main structure is cross laminated timber panels (walls, roof, floors), and steel portal frames.
The build
One of the things Julie likes about using cross laminated timber is that much of the house could be prefabricated.
“My background is in Europe and the way we build is prefab; having a product that was prefab was a big thing. The shape of the house was built in a week: on Monday, we had nothing; by Friday, we had a floor, a roof, walls – no windows, but the shape was done.”
Julie says building a house this way is different, but has big benefits.
“In general, the cost of materials is more expensive at the beginning, but the time to put all the panels on site is usually really short. In our case it was four days. For a house with a standard timber (stick) frame, the cost of materials is really cheap but you're going to spend five weeks with labour to put it all together.
"At the end the cost should be even, if you leave it unfinished. If people start to plaster a simple CLT wall, you're adding material, and the cost that goes with it, and this comparison won't be legitimate anymore."
Julie followed the higher building standards in the UK (for insulation) and France ( for airtightness), rather than the minimums set out in the NZ Building Code. That's why her house is the first in NZ to use wood fibre external insulation. The thick timber boards are screwed to the outside of the CLT and covered with a weathertight membrane.
“When I was working as an architect in Switzerland, this product used to be my standard. When we decided to build our house, I didn't take a lot of risk because I knew the product.”
The windows
The double glazed windows have thermally broken aluminium frames that open upwards (read more on page 30) or are casement windows that open sideways for better air flow.
The three-stacker sliding doors open both ways, a new, untried idea for the supplier.
The windows are also sound-proof, important for this house which is just 350m from the busy Port Lyttelton.
“The port is really noisy, especially when they've got boats unloading scrap metal. The windows are designed to have a decrease of 36db from the inside to the outside so it's very quiet inside.”
Ventilation
When you have a highly-insulated, airtight house, it needs a good ventilation system to remove moist air, bring fresh air in, and maintain comfortable humidity levels.
The windows play an important passive role. The upward- opening ones allow hot air out. The casement ones are perpendicular to the prevailing wind, allowing the couple to direct the outside breeze through the house.
“If it's windy and we want to open a window, you're not having a tornado going through the house.”
Two roof windows create a chimney effect, sucking hot air out on warm days.
But this smart house also has a decentralised, balanced ventilation system. There's no roof space for big ducting pipes used in common, positive pressure systems. Instead, small units in the bedrooms and a big one for the upstairs area, ventilate the air and recover heat at the same time.
“Each one has a little fan with a ceramic disc,” says Julie. “You're warming the air in the room; the fan is extracting this air out for 90 seconds; the heat is stored in the ceramic disc. The fan stops and reverses and takes fresh air from the outside; the air goes through the ceramic disc, it prewarms it, and it goes back into the house.” Julie loves its simplicity, and the figures. “You're recovering up to 86 percent of the heat. You get fresh air, but you're not losing the heat, so that's a major advantage. And it costs us $13 a year to run (3 cents per day), so it's really cost effective.”
The bonus is Julie and Edward can enjoy the port view without smelling it.
“I can tell you this morning, we had two boats refuelling and it was smelling like petrol outside. This ventilation system has filters, so you don't have the pollution coming in.”
The result
When Julie is coaching people in her eco design advisor role, she uses her own house to show them what is achieveable.
"People might think you can't do concrete on a first floor, and I'm like, that's not true. They might think underfloor heating is really expensive, and I can say it's not true, I've done it and this is how you could do it.
“I really want to show people that you can do things differently. That's why I'm happy to share what we've done."
In 2018, the couple took part in the Superhome tour of Christchurch which showcased innovative houses built to very high standards, using smart design and products.
“For me, it was important to be open. We had 1500 people come through the house over three weekends.
“In my heart, I don't want people to copy this house. I want them to grab something they like and use it in their own design."