It’s a steep run down Black Fyne Bank through Shottley Bridge towards the broad, steep sides of Derwentside. In this part of County Durham, Victorian terraces and newer red-brick estates in old industrial villages follow the roller-coaster contours with impressive tenacity.

Claire Cranston, daughter of these northern slopes, had never given them a second thought until recently. She had never marvelled how populations drawn by the Durham coalfields could make their homes on hilltops or streets descending dramatically to dale bottoms. She had never considered what a dog’s life builders must have with never a flat piece of ground. Not until two years ago that is, when this 26-year-old science teacher let her then fiance talk her into building their own house. And not any old house, but a four-bedroom home on four floors - with basement as well as attic rooms - cut into the steepest bit of hillside imaginable, a building plot with wildly vertical ambitions.

Since then, this labour of love has taken up almost every weekend and evening. Now, their home-in-the making occupies the last plot in a cul-de-sac of self-build houses just off Black Fyne. It looks conventional from the front, but its foundations plunge down the hillside at the back. Inside, three flights of stairs climb like a lighthouse, opening out on to rooms, including laundry, games room and study, giving vistas of Derwentside and Northumberland beyond.

During the summer holiday, Claire divided her time between teaching forensic science to able and talented children at a summer school and making the most of long daylight hours as a labourer. Her black belt in karate has given her the stamina to help her husband and fellow black belt, Stephen Richardson, 29, realise a long-standing ambition.

Although they raced to make at least one room habitable before their wedding in August, having completed the wiring, laid on water and built a garage over the summer, they have had to put the moving-in date back to Christmas, by which time they hope their plasterer will have finished his work. This term it’s back to evenings on the building site.

Following a week’s honeymoon on a Greek island, Claire is finding being back at the grindstone doubly difficult. “The evenings are hard at the start of term, with so much school planning to do, and then having to go down to the site. But it will be worth it,” she says. Stephen and Claire estimate that their house, once finished, will be worth between pound;160,000 and pound;170,000, a high property price for the area.

Claire, who teaches at Kingsmeadow comprehensive school, Gateshead, admits that through last winter especially, after tiring days and with lesson preparation to fit in, she was a less than willing worker. “I’d come home from school and put my feet up; then there’d be a call from Steve - ‘Are you coming down then?’ I don’t think my colleagues could quite believe I was taking this on. They laugh at me now, though they say they are all ready with the paintbrushes. It’s been hard work, I’ve been going in an hour early to get through school work, but it’ll be worth it.”

What Claire doesn’t know now about digging foundations, putting in windows, plaster boarding ceilings, cleaning up copper piping and laying floors isn’t worth knowing, but when they acquired the plot she knew nothing. “There was just a steep hill and a load of mud and rubble . I couldn’t imagine how it was going to work. I thought houses somehow got built without too much trouble.”

Stephen admits to having the odd sleepless night, especially when it seemed the house might rise too high to satisfy the planning authorities. Their appeal last November delayed building while the house was roofless with winter on its way. When they won, Stephen rounded up his three brothers and various nephews to get the roof on by Christmas.

Claire, the daughter of a welder in Leadgate, met Stephen 12 years ago, when she was still a pupil at Black Fyne secondary up the road, determined to carry on studying and become a teacher, and he was a young roofer. Stephen, son of a steelworker in Consett, was keen to enter the building trade but soon became disillusioned about standards. “You’d see houses go up that quick. There’d be nothing to them at all. I have always thought about building a house for myself, because I wanted to do it properly.” He now makes tools for a mobile phone company but the craft of building has remained his passion. He designed the house and has worked with the help of mates from the trade. But lack of funds has forced the couple to do the bulk of the work themselves, encouraged by the thought that their unique home will cost them half the price of a ready-built equivalent.

Claire has become proficient at clambering up scaffolding and carrying out Stephen’s instructions. She acknowledges that building a house together has been a sure-fire way of testing the relationship but that they’re both “pretty cool” when things go wrong. Perhaps her science and maths has come in useful? “Not really,” she said. “I calculate in centimetres and metres and Stephen works things out in inches so we’ve just about confused each other; but we’re getting there.”