T-shirts and shorts are all you will find Kevin Tattersall in at home and why not, when the average temperature inside is in the early 20s.
"When it gets to 18degC we feel the need to light the fire."
It is one of the nice perks of building a passive solar house - constant warmth.
The day the Otago Daily Times visited it was 16degC outside but inside it was a very cosy 24degC, with no heating.
"When we went to bed last night it was 20degC and when we got up it was 19degC," he said.
During a particularly cold patch during winter when the temperature in the bedrooms dropped to 16degC, he and wife Kaye reached for the winter duvet for a couple of weeks, but that was "a rare event".
"We put in underfloor heating but we haven't needed to hook it up yet."
But getting to that stage had been a long process.
It began when the couple went on a solar home tour many years ago when climate change and global warming were becoming hot topics and decided they liked the concept.
Then they found the Signal Hill block - a very steep 2800sqm section - and began to plan and design their long, narrow 150sqm, two-bedroom concrete home which is set back into the hillside.
"The whole house is like one big concrete bunker which absorbs all the heat."
It was constructed of concrete blocks and insulated concrete panels which required a crane and many hands to get down to the site which faces Northeast Valley.
No internal walls were needed for structural integrity but they had been installed for "purely thermal mass" reasons although they also provided nice features and privacy.
The flat-roofed concept meant another storey could easily be added and the design of the stairwell meant there were options to have two entrances or two separate dwellings.
"We were thinking about the future."
The home was topped by a Zincalume roof which reflected nicely on the solar hot water tubes.
Its front faced north-northwest and was mostly floor to ceiling double-glazed windows and doors.
They liked the industrial design concept which meant they did not have to worry about "fancy finishes" and were able to cut costs and save resources as a result.
That meant there were no ceilings in the house so all the lighting and electricals were exposed on metal cable trays.
"I saw these type of ducts at the university in the information centre and library and liked the idea - I thought they worked well with the industrial theme of the home."
The industrial theme continued with bare concrete floors throughout and an open-shelved galley kitchen which features a concrete bench.
To keep their energy consumption down they had only put in a two-burner gas hob and used a small combination convection-microwave oven.
All of the internal doors of the home were recycled and all had glass in them to allow light into the back of the house - the back wall of the hallway is the concrete block retaining wall of the house.
"We wanted to put it into the hillside so the earth could act as extra insulation."
Mr Tattersall took on much of the labouring, project management and finishing of the home and 8-year-old daughter Georgia helped make the mud bricks which were used to create feature walls and provide more thermal mass in the house.
"It was a great family thing to do. We did it over one summer, it was hard work and we cursed it at the time but looking back we enjoyed it."
The mud bricks were constructed in sections separated by lengths of macrocarpa and linked by an invisible wire to hold them in place during an earthquake.
They had opted for a low water-usage system for the toilet and bathroom and hoped one day to collect their rainwater.
If there wasn't enough solar power to heat their water, they put the wetback fire on. The water cylinder, laundry and storage were tucked away under the entry stairs.
The wall of windows and sliding doors - double glazed with thermally broken aluminum - in the large open plan kitchen, dining and office area meant it was always a few degrees warmer than the bedroom end of the home which meant it was never too hot to sleep.
The warmth also meant it was a perfect place to grow tomatoes and other vegetables so a small garden had been set up in the office area with some tomato plants growing nearly to the roof.
And no, it did not get too hot in the summer.
During last summer's 32degC days inside it was a nice 25degC as the thermal mass absorbed the heat not releasing it until the sun went away, he said.
They also had windows for cross ventilation. As a result their power bills averaged about $35 a month.
"There was the extra cost of building but the savings are really and truly there."
The home cost about $350,000 to build and was still a work in progress as he believed in getting the basics right first, but it was an enjoyable process.
"It's very rustic, raw and individual. I'm the guy with no ceilings but to me it makes sense."
So much sense, the family was now making the most of the other parts of the section, fencing it off for a small family of Swiss milking goats, planting a vegetable garden and fruit trees and planning to buy chooks.
"It's become a lifestyle. It's a lot of work but it's really enjoyable. It fits our values.
"It's going backwards but going forwards."
