Smart Series: the 10/10 house
Designer Warren Clarke is so passionate about smart homes, he built one of the smartest in NZ.
Why Warren Clarke’s home is one of the smartest in NZ
If there's one thing Warren Clarke would change about his small, smart house, it's the size. At 140m², it's already 42m² less than the average NZ home, and he'd make it smaller. “Somebody asked me, if I could do it again, what would I change? I reckon I could take 10-15m² out of it and it would still be amazing.”
Oversized, inefficient houses are one of Warren's pet peeves. He spent years working for a building company, designing bigger and bigger homes that met the minimum standards required under the Building Code. Under the code, an inefficient, poorlyinsulated, expensive-to-heat home still meets the minimum standards.
It annoyed Warren so much, he went to work for design company, Nook.
“Budget and cost were always paramount. I learned ways of designing houses so that they captured the sun better, were warmer. I tried as much as I could to get more insulation into them and make them more energy efficient, but there was always a pushback from the client: what's it going to cost, what's my payback for that sort of thing?”
Warren's argument is that an efficient home is going to save you money for decades. He's observed power prices have gone up 100 percent every decade since the 1970s.
“If your house today costs you $650 a month to heat, in 20 years' time it's going to be $2500. If you invested that $2500 in the build in the first instance, you wouldn't be spending that. ▶ Continues on page 30.
“I could have built a 200m² home and it would have cost me $4000-5000 to heat it ( yearly). Instead, I have a 140m² home and I can heat it for $1500 a year.”
Building smaller means money can be invested in products that will keep the house warm and energy-efficient for a lifetime.
A small house has other benefits. Warren’s first design included a garage.
“But we had to save some money and I thought, ‘right, we’ll have a storage box with a carport’. It’s the best thing that ever happened – you don’t have so much junk! You look at things and go ‘how important is this to me?’ I went through 20 years of garage junk, and said, ‘nope, I haven’t used that, nope I haven’t used that. It was cathartic.”
The Brief
Warren’s home was inspired by his clients. They would often ask what was the ‘payback’ on size and cost. Warren decided to find out.
“I thought, I’m going to build a house, we’re going to live in it for 3-5 years and we’re going to find out once and for all what’s worth it and what’s not.”
A good smart home will be much smaller than the NZ average of 182m² (rising to 217m² in Auckland). Money saved on building extra square metres can be invested in products and technology that will make it a more efficient, warmer, and healthier home for 50+ years.
Warren’s initial idea was to design a house that would be a 7-8 on the Homestar rating scale (see page 35). But his builder was more competitive.
“He asked me, what would take it to a 10? I told him: acoustics, solar panels, greywater recycling. He said ‘let’s give it go’, and we did it.”
The design is passive house, and Warren also followed the basic principles of smart, small homes (see page 30).
A 10 Homestar house is built to world-leading standards, with strong sustainable credentials. Warren’s home is only the third in NZ to pass the stringent quality assurance tests, overseen by the independent Green Building Council of NZ.
"It's the best thing that ever happened – you don't have so much junk!"
The Design
Many of the features of this house are things you can't see, but each one played an important part in gaining that magic 10 rating.
The waffle slab floor (also known as a ‘raft' slab) sits on a special layer of insulation. Another insulation layer wraps around the edges (80% of heat loss is out the sides of a concrete floor). It is also an important part of the home's heating system (see page 34).
A waffle slab sits above the ground so it's easier and cheaper to install than traditional footings which must be dug out. Styrofoam pods sit in the concrete, reducing the amount of concrete you need to use. This also makes the slab lighter, allowing you to build on soft soils.
It's seismically strong. That's important when you're building a house in the still earthquake-ravaged suburbs of Christchurch, says Warren.
“In an earthquake when the ground moves, (the foundation) just sits there and vibrates – it floats like a raft. I came to Christchurch in 2011 after the earthquakes, and I had been using raft floors for 4-5 years before that. But it was new technology to Christchurch, they didn't know what I was talking about. Now, it's virtually standard.”
The laminated veneer lumber framing wood is 140mm wide, instead of the conventional 90mm. The extra thickness helps to insulate the house; standard 90mm timber framing acts as a thermal bridge, transferring heat out of a house due to its narrower width.
A 50mm cavity runs around the inside of the framing, to house pipes and cables, maintaining the integrity of the airtight layers.
“The framing becomes a rigid air barrier, and you don't want to penetrate that, so all my wiring and plumbing goes into that service cavity. It means I can cut holes in the walls, put in electrical plugs and put my taps out through it, and I'm not puncturing (the rigid air barrier).”
It's an added cost to put in a cavity like
"In an earthquake when the ground moves, (the concrete floor) just sits there and vibrates – it floats like a raft."
Warren Clarke
this, but a well-thought-out layout can save you money. For example, if bathrooms and the kitchen sit along the same external wall, you only need a cavity along that wall, not all the way around the house.
“It's that whole thing of looking and planning at the design stage," says Warren. "You can plan savings.”
To gain a 10 Homestar rating, Warren had to think about air quality. A special ventilation system keeps the air fresh, while still retaining heat (see below).
He used H1.2 treated wood that prevents fungal and bug infestation. It is low VOC (volatile organic compounds), meaning it doesn't release much (or any) toxic gas or vapour. It's covered with building wrap so any gases that are produced can't get inside the house.
“We also used an organic, natural paint finish on the plaster walls, and no formaldehyde.”
Two other features to help the house reach 10 Homestar are its rainwater storage tanks and a recycling greywater system. The greywater from the shower, bath and vanities is recycled, then used (along with rainwater) in the toilet cisterns and laundry.
The Heating Underfloor hydronic heating system and air-sourced heat pump
This system moves hot water through pipes in the concrete floor. An air-sourced heat pump warms a 360-litre hot water cylinder. Hot water is taken from the bottom of the cylinder and pumped through the floor.
Heat recovery air ventilation system
A heat recovery ventilation system refreshes the air in the house, helping to control humidity and prevent mould.
“When you have a lack of air movements, you've got to mechanically vent the house, or you get a build-up of condensation, a build-up of CO₂, and you'll have problems with mould," says Warren. "We extract the warm, moist, dirty air; the incoming, clean, cold air passes the outgoing air and the heat is exchanged… it's 80% efficient.
“The heat pump and our underslab heating give us a lot of gains. But also, being near-passive, we build up our thermal mass so our concrete slab becomes almost a battery, storing heat.”
OM solar ventilation
OM comes from the Japanese words ‘omoshiroi' (interesting) and ‘mottainai' (nonwasteful). It's a series of vents and fans that suck warm air in during the day and down ducts into the house to help warm it.
Warren's system was designed by a friend and integrated into the ventilation system.
The Result
A year later, Warren's house has passed the stringent testing by Homestar, scoring the highest possible rating. His house is only the third in NZ to reach a 10.
“I still wander around my house and look at it and think ‘wow, it's amazing', and I've been living in it for a year.”
He's now working with clients who want smarter homes, and with builders who are keen to to try the new techniques and products needed to construct them.
“Often people come to us and they're already of the smart house mindset: they've often researched it for 3-5 years, they've been to open homes. They know in their bones if they go to a volume builder, they're not going to get what they want.
“You tell them you can take the budget they've got and build a smaller house, but it'll be much more energy efficient, much nicer to live in.”
Warren says those in warmer climates could learn a lot about building smarter.
“Aucklanders don't think they need to worry about energy efficient housing, but it's not only for places with cold winters. Smarter houses are warmer in winter and cooler in summer. It benefits everyone, from Bluff to 90 Mile Beach.
"We've had days here where it's 30°C outside, and we can maintain 25°C inside without cooling it."
Most people think short term, says Warren. They build enormous, inefficient houses and put their budget into what he calls ‘bling'.
“We've spent too many years going down a path where we build rubbish housing and go for granite benchtops and the most expensive tiles. Then you find it costs $500 a month to heat.
“If you have a smaller, smarter home, it's easier to heat, easier to maintain.
"The problem is we don't treat our homes as a home, we treat them as a financial asset, and that's just wrong.”