Published by Grania Litwin/ Times Colonist
April 4, 2014 10:52 AM
Damon Gray calculated precisely how much shade falls on his roof when planning to create a solar powered, concrete sandwich panel home. He believes a home should be a legacy for the future, but it should also be a place to keep a family healthy, comfortable and safe, without costly maintenance and excessive energy requirements.
That’s why, when the New Zealand-born builder wanted to create a home for himself, wife Annie and their two children, he used concrete “sandwich,” tilt-up construction, and installed 54 solar panels on his roof.
“It was difficult to find someone who would design a house like this, so I did it myself and many details were inspired by my mum.
“She was a cleaner of high-end homes in New Zealand and always picked out the flaws in the buildings. I took it all in when I was growing up,” said the owner of NZ Builders who has studied alternative energy for years.
He said much of it is based on common sense.
“Of course you want to have your kitchen facing the morning light, sunrise in the east, so you get that brightness and warmth. And of course you should have the dining room and master bedroom facing west, to take advantage of the afternoon sun.”
Damon, 33, who trained as a carpenter in New Zealand, worked there and in California for eight years before moving here. He has been building in Victoria for nine years, and his home, with interiors by Robin Bryson, is featured in the April 12 and 13 Young Life home tour.
“Electricity costs in New Zealand are three times higher than here,” and that reality taught Damon that overhangs and window heights control heating and cooling, so there is less heat fluctuation and less reliance on mechanical systems.
“Winter sun comes in at an angle of about 19 degrees here, and that allows the heat to warm concrete floors. But in summer the sun is higher, more like 60 degrees, and the shadow line of overhangs covers the windows,” so you don’t need air conditioning.
He said tilt-up sandwich construction, with insulation between two layers of concrete, was developed in Germany and is common now in Europe, New Zealand, Australia and Japan.
For this home, Damon used a two-inch outer wall, four to eight inches of insulation, and five-inch interior walls for a total thickness of 12 to 14 inches.
“Insulation is cheap so I always use lots of it,” he said, adding the walls are built on site, on steel casting tables, then tilted up. “The accuracy is super high, to within two millimetres, and there are no gaps to let air in. It’s a complete blanket wrap.”
In some places the exterior looks as though it’s made of planks, but that’s because of an “architectural” impression, made by pouring concrete on planks. He then peeled the boards off, turned them around and reused them for exterior soffits.
“There is almost zero maintenance in a concrete house: You just have to check the caulking joints every five years and apply exterior sealant every 10 to 15 years.”
And Damon is a big believer in sunlight. “Turning a house just 13 degrees on a site, can increase your solar gain by 15 per cent.”
In this house the roof panels face due south, measure 2.5 by 5 feet, and cover 30 per cent of the roof. His roof slopes from 10 feet at the front to eight at the back — “You have to find the sweet spot of tilt” — and gets an average of five hours of sun a day, year round.
But every property is different and requires acute analysis.
He looked at a full-sun property down the road in North Saanich, but it cost $150,000 more. So he opted to save money and buy this lot, although it has only 73 per cent sunlight. He could take down more trees, but he likes them.
“It would cost me about $1,200 to take them down, and with that money I could buy three more panels … there are always trade-offs,” said the builder, who will be on site during the tour to answer questions.
“I went through every heating option on the face of Earth when building this house, even wood burning. But you’ve got to cut the wood, season it, what’s your time worth? What does a cord of wood cost? And you still need electricity to run computers, appliances.
“Geothermal would have required a capital investment of about $33,000 and you still have to pump energy around the house. A heat pump-to-water system would be about $27,000 and you’d still need pumps.
“Forced air electric is about $15,000, but we really wanted radiant floor heat ….
He has opinions about gas, too. “Gas is three and a half times more efficient than electricity. If it saves you $1,200 a year on heat, that represents $25,000 in money borrowed, so if a building lot has no gas it should be $25,000 less expensive.
“We get 2,000 hours of sun a year here in Victoria, and that number is going up every year thanks to climate change. B.C. Hydro rates are going up every year, too,” so he reckons his savings will get bigger and bigger — and solar was his best option.
His system cost about $36,000 and the four-bedroom, four-bathroom home cost $280 a square foot to build.
His average electricity bill is less than $70 per month, but he explains it’s about more than saving money. It’s about saving power for others, and saving the environment, too.
“You have to produce 60,000 kilowatt hours of power at an Interior dam to get 20,000 kilowatts on Vancouver Island. That’s a lot of power lost in transmission. So if we can produce 20,000 kilowatts here, we are saving maybe 40,000 for users closer to the dam.”
A typical home uses about 27,000 kWh per year, but his home is far from typical.
His 3,000-square-foot building will produce 14,000 kWh and because of energy efficiencies the building uses only about 16,000 kWh per year.
The house is set up for rainwater recovery too, but as his water bill is only $200 a year, the motivation is not there yet.
He doesn’t store surplus energy in batteries. The solar panels provide energy for the family’s immediate needs — whether running the stove, drying a load of clothes, heating the floors or running the Heat Recovery Ventilator. The excess goes back to B.C. Hydro.
“So in summer we build up credits, and in the winter we take them out.”
A massive concrete wall inside the house, by the kitchen, helps store excess heat from ovens and other appliances. “Dumping heat into the walls is a good way to reduce temperature fluctuations, or thermal lag, and create a healthier indoor environment.”
Damon says concrete construction also has many advantages in addition to being energy-efficient and seismically engineered.
It is fire resistant as well as rot- and pest-free. It’s healthier because mould cannot grow on it, and it has a low carbon footprint considering the life of the building. It also transmits almost no sound and creates low waste during construction.
His dumping fees were $1,600 compared with his last house, which sent $8,600 worth of waste to the landfill, and he used excess casting material to make garden dividers and his outdoor picnic table.
The HRV, roof membrane, windows and gutters are all European and the gutters are round, which makes them easier to clean — a tip from his mum
Concrete panel construction costs about 10 per cent more than wood frame but the difference is recovered through lower heating and maintenance costs, said Damon, who has built some fancy houses in his time.
In California, he worked on many $1,000-per-square-foot-plus houses. One project employed 150 finishing carpenters for two years and he had to sign a privacy contract, so can’t reveal the owner’s name, but he was a big shot in the computer industry.
“I ran a crew of 15 and we did things like install three $30,000 garage doors.”
He worked on another home that sold for $40 million, but now specializes in building energy-efficient, concrete homes here on the Island.