A considerable building - 400sq m, with five bedrooms, a double garage and lots of living space - its lower storey has a concrete slab floor, with steel reinforced concrete frames with cob infill for both interior and exterior walls.
The upper storey is more conventional, with wooden framing, gib board lining and plywood board and batten cladding. The windows are wooden and recycled.
The Aims put countless hours into their building project. Mr Aim, a senior policy analyst at Wanganui District Council, is pleased with the result.
He said it was lovely to live in, with the earth walls moderating humidity and keeping the house warm in winter and cool in summer.
His wife died unexpectedly in October last year, but had achieved much of what she wanted with it.
The cost has been a bit less than a conventional house of that size and style - but not much less. There were extras like water and septic tanks needed because of its rural location. Mr Aim doesn't know the full cost.
"I've never done that exercise, because it could be upsetting," he said.
The Aims never set out to build in the country. But Ruth noticed an ad for land in the swampy valley south of Lismore Forest, with birds such as spotless crake and fernbird and under a Queen Elizabeth II covenant.
They bought the land in 2001, without planning to build. Then they visited Ruth's brother in Tasmania and saw a mudbrick house. They investigated mud building and decided mudbricks were too heavy and awkward and rammed earth was too technical. Cob appealed because it is more forgiving.
"If it's too soft you can pull it off, and start again next day."
The house was drawn up in accordance with their ideas by architectural designer Margaret Robinson.
The design complied with New Zealand's earth building standard, and there was no problem getting it okayed by council. Builder Reg Dilloway did the concrete and wood work, leaving walls to be filled in.
The Aims moved into the first half of the house in April 2010, before it had television, running water or a flush toilet.
They've since got satellite TV and a septic tank. Electricity is provided by a generator and photovoltaic panels, because it would have cost them $40,000 to put in a power line.
The wall building exercise happened at weekends and on long summer evenings. It's heavy and tiring work.
The cob mix is 60 per cent clay off the property with 40 per cent shellrock fines and a couple of handfuls of straw for each batch in the concrete mixer.
The mixer has survived the long task, but the couple's kitset wheelbarrow finally collapsed under the strain.
The external walls were finished in 2011, and the internal ones just before Christmas in 2012 - after a spectacular collapse on a humid day in December.
"We were going like the blazes, and we were 18 inches from the top of the wall when I heard a noise and turned around," Mr Aim said.
What he saw was 1.5 tonnes of carefully placed cob sitting on the floor, and blocking the stairs to the bedrooms.
All of it had to be rebuilt, and there was a bottle of champagne when that was finally done.
The finished walls are plastered with a 60:40 mixture of sand and mud respectively, then whitewashed with a mixture of hydrated lime, salt and water that's "almost free".
The upstairs still needs gib stopping, plastering and painting.
The house achieved code of compliance in August 2012 - the occasion for another celebration.