Seventeen years ago my elder brother joked that we would end up buying a house together, as clearly I was never going to find a boyfriend. It seemed a typical teenage jest at the time. However, that day has now come to pass, and while the arrangement has its downsides, buying with a sibling has proved an excellent way of getting on the housing ladder.

It all happened rather by chance. My husband, Garnett, and I emigrated to Canada in 2003 from Scotland with pots of money from a fertile property market. However, we bought badly in British Columbia, had a third child, received letters from the local school warning of cougars in the playground, and decided that perhaps the UK wasn't so bad after all. We scurried back to Britain in 2004 with little cash and found that house prices were booming, so squatted in my grandmother's house near Portsmouth.

My brother, Martyn, had bought a three-bedroom terraced house in Portsmouth, had a daughter of his own - Isobel, now three - and was worrying about the schools where he and his partner, Su, lived. It was on an early spring afternoon in 2005 that our mother mentioned that a family friend was selling her property - an eight-bedroom, virtually derelict seaside house in Alverstoke, Gosport, Hampshire. The vendor had planning permission to turn it into three flats but had had no interest from developers. She wanted £400,000; quotes she had obtained put the cost of conversion at £100,000.

We all went to look and while the children - Griffin, 8, Hebe, 5, Orla, 3, and their cousin Isobel - played tag up and down the two staircases, in the four public rooms and the gloomy cellars, the idea of buying together took hold, with the intention of splitting the property into two houses.

Our first hurdle was that the vendor gave us exactly one month to sell my brother's house because she had had late interest from another party. The second was that we had to find a mortgage that could accommodate four adults, only one of whom, my husband, was in full-time employment (he is a statistician). My brother was taking a photography degree, his partner worked part-time for IBM, and I had no real income as a full-time mother. Our third hurdle was working out the intricate equations of finance. My brother had a huge pile of equity and no ready income, so it was essential that his mortgage repayments stayed the same. We had very little equity, but income. Utilities, council tax, the TV licence and insurance were to be split down the middle, as were the costs for solicitors and the deed of trust (our working agreement, which enabled either party to force a sale with a two-month warning).

There's a photograph of us on moving day, in April 2005, in which we all look sick. No one was confident that we were doing the right thing but with the £100,000 building cost in our minds and the fact that the vendor had dropped the price to £350,000 (plus a £7,000 penalty, as we didn't make the one-month deadline), we all believed that we would be reaping enormous financial benefits in the long term.

The first few months were the hardest, as we crept around each other's emotions. Once the honeymoon period wore off the reality of sharing a kitchen (cupboards, crockery, utensils, dishwasher but not food, tea bags but not coffee) sunk in. Bizarrely, although we cooked separately, performing a dance around the two burners and one oven shelf each, we all sat down at the jointly set table at the same time. Washing up for eight - the same as for Christmas but on a daily basis - was split according to a rota. Bathroom cleaning and vacuuming were shared between us weekly, although no one ever took responsibility for dusting.

Living with someone, as we all know, is a game of give and take. But imagine sharing a house with another two adults and their child, and managing absolutely everything by committee. Add to that the different parenting styles, the patterns of domesticity, and the angles of marriage. We couldn't bicker with our spouses in the communal rooms, or wander naked down the hallways. It was like being on continual show, on best behaviour, managing tempers and tantrums from all eight occupants of the house.

The children coped admirably (aside from supper envy when the others had pizza), as only Griffin, my oldest child, can really remember what life was like before multi-occupancy. Lines were quickly drawn about territory, what belonged to whom and whether toys could be borrowed without permission. Anthropology became a reluctant hobby and it wasn't long before all the adults were retreating to their private rooms and the communal ground floor lay empty. We realised that we were not there to share each other's lives, just living space.

Luckily we had enough room to get away from each other and we had an end point in sight - the splitting of the house into two. Although the plus points, such as live-in babysitters, company, borrowing of baked beans and economies of scale, were great, they could not preserve our sanity long-term.

The building works are now in progress and we have all retreated to small rented flats for the duration. The £100,000 budget turned out to be laughable - it was a guesstimate, really, as the work will cost more like £200,000. It is a huge building project, scheduled to take six months, which will be just about the right amount of time for us all to regain our personalities and to forgive minor infractions (such as opposing styles of washing up).

I speak to my brother regularly and I can't wait to have his family as neighbours - but perhaps not as housemates...

FACT FILE

Hold regular meetings.

Create a joint bank account from which all bills are paid.

Have a firm timetable in place for all works.

Clear legal agreements are absolutely essential.

Leave your emotions at the front door.

Times recommends

• Second homes: credit crunch casualty or money-spinner?
• How I built my own sliding house
• Top 10 incentives for house buyers