Buriano, a Tuscan hamlet near Pisa where relics are being incorporated into a redevelopment

Skeletons are quite crumbly when they are very old. A bit like an Aero [chocolate bar] but white,” says Edward Waterson, who recently found the bones of two Romans underneath his home.

Waterson lives in the northern city of York, Viking capital of England and a former Roman garrison town. Consequently, his home, which is only five minutes from the ancient centre, is the icing on top of a layered cake of history. “Every site is potentially of archaeological interest,” Waterson explains. When he sought planning permission to knock down his 1920s house and rebuild, consent was conditional upon him allowing an archaeological dig to take place. It didn’t take too much sifting before a burial ground was discovered.

While most homeowners would be thrilled to discover ancient artefacts, though possibly not human remains, under their foundations, many are less sure about having their property unexpectedly turned into an archaeological dig. So what happens in the rare event of a simple extension becoming a complex excavation?

“As soon as we started going below current ground level we had to have an archaeologist on site with a ‘watching brief’,” says Waterson, a negotiator with estate agency Carter Jonas. The local authority’s archaeology adviser recommended an expert, and “every time the digger dug he [the archaeologist] was there seeing what was below the surface”.

Ownership of historical remains varies considerably from country to country. In France, for example, they are shared between the landowner and the state, whereas in Spain they automatically belong to the state. Italians, however, own any remains found on their property, though the state insists (and can visit to check) that they are maintained.

In Britain – where the rules are very similar to those in the US – the landowner owns everything except a body, in which case the police need to be informed, or a treasure trove (generally gold and silver objects and groups of coins more than 300 years old, prehistoric metal and their containers), in which case a coroner must be informed.

Property owners in the UK who find artefacts such as vases, pottery or jewellery are encouraged to inform their local museum or the British Museum. “Then they can record the find and possibly buy it,” says Robert Whytehead, head of the London regional archaeological division for conservation agency English Heritage. Uniquely, the British Museum has a portable antiquities register, a voluntary scheme to record archaeological objects found by the public.

Waterson’s archaeologist was on site for two weeks while the foundations were excavated. The unearthed skeletons of an adult and a child were found, removed and recorded. While one area was being examined the builders worked in another part of the site “so the delay was only a maximum of a day or two”, says Waterson. He met the cost – mainly the archaeologist’s time – of roughly £2,000. “If I had been told to have a complete excavation of the site, which could have been the case, it could have run into hundreds of thousands of pounds” he says.

Fortunately, at an individual property level, big archaeological digs are rare. However, laws making excavations of historic sites part of the planning process in Britain came into effect in 1990 and most now occur in connection with large housing developments.

“The rule of thumb is to allow roughly 25 per cent of the development costs [for an excavation],” says William Anthony of Knight Developments in Colchester, eastern England. This cost is generally deducted from the price of the site so, in the end, it is the landowner who foots the bill. An excavation can take a few days, several months or even years. “It’s when you find something unexpected that problems arise,” says Anthony.

Building industry stories of ancient chariot burial grounds or bronze-age villages being discovered and delaying a housing project or new road by up to two years are common. And in places such as Florence, Renaissance capital of Italy, it is a brave developer who digs too deep.

“There is an unwritten rule [in Italy], which is: think very hard before you announce to the local authority what you have found. It can be a real nightmare,” says Bill Thomson of agency Knight Frank’s Florence operation.

He is selling apartments (from €465,000 to €2.5m) in Palazzo Bardi, a converted former school that was originally a Renaissance palace in the heart of Florence. As the lime green paint and false walls were removed, 16th-century frescoes were found. Nearby, the original 14th-century courtyard was discovered and identified as being by Brunelleschi, the architect behind Florence’s world famous duomo . Beneath this was yet another layer of antiquity: Roman tanneries.

“The question is ‘Where do you stop?’ Do you go for indifferent Roman or for Brunelleschi?” says Thomson. “We took photos, recorded the tanneries and then [legitimately] poured rather a lot of concrete over them for the new drains. It was more about preserving what Brunelleschi was trying to do. Archaeology puts developers in a very, very difficult situation.”

Not surprisingly, the temptation simply to hide archaeological finds is huge. “I don’t approve of this but I do know of remains being covered [illegally] with concrete. You’d be surprised how fast they [a builder/developer] can move before an archaeologist can get there,” says Waterson.

Recent laws have, however, made the hiding of finds far harder (in the UK at least) and, many would argue, very difficult to pull off. “The truth of the matter is that most areas in the UK are quite well documented and I think quite well controlled. I do not think as a developer you would ever get away with it,” says Anthony.

Palazzo Bardi, originally a Florentine Renaissance palace, where apartments are now being sold

Knight Developments’ Secret Garden is a collection of 24 apartments ranging in price from £215,000 to £320,000 on a site next to a Norman castle, which in turn is thought to have been built upon the remains of a Roman temple. It is therefore listed as an ancient monument and comes with “the highest planning restrictions you can get,” says Anthony. The building permission was conditional upon a dig that revealed old Roman streets, house floors with mosaic tiles and pottery. After being recorded and documented, the site was carefully covered up again, in a manner that would ensure its preservation, and the developer was then allowed to continue building on top.

“If we had found something really important we might also have needed specially designed foundations so as not to disturb what’s underneath,” Anthony says.

Often a building plan, particularly the foundation design, is adapted to preserve as much archaeology as possible. “What we are trying to explain to people is that archaeological resources are finite, and if you dig through then it’s gone and you cannot bring it back, which is why we need to make some record,” says David Thomason, assistant director of Oxford Archaeology, one of the biggest private archaeological firms in Europe. “Most archaeologists and curators will try their utmost to work with developers and the public to see that the best outcome for archaeology and [building] designs are reached,” he adds.

Despite the challenges that artefacts can throw up, most homeowners are generally thrilled to have an excavation. And if a find can be incorporated within the home, all the better. For example, 13th-century graffiti was found in the basement of a Mallorcan palace in Palma. Originating with the Knights Templar on their way to the Crusades, it can be loosely translated as: “Sod the Arabs. John Paul”. The owner kept it, covered it in Perspex and proudly displays it in what is now his dining room.

More common archaeological features restored within homes include frescoes, ancient stonework and historical family crests painted on to the old walls. “Such aspects are fundamental to any restoration and very popular,” says architect Nicoletta Novelli, who is redeveloping Buriano, a protected Tuscan hamlet near Pisa, where one-bedroom apartments start from €350,000. “Historical artefacts help us keep the character of a historic building.”

Where ancient finds are simply too large or complicated to incorporate or remove and restore, they are often quite simply recorded and put back.

Ovens originally used by the New York English Muffin company in the 1850s were discovered in the foundations of a 19th-century town house worth more than $690,000 in the fashionable Chelsea district of old New York. “We thought about putting a glass window [over them] but it would have been very dark and, to be honest, not much to see,” says Kerry McInerny, the owner. In the end she resealed them and put a plaque up outside the house, detailing their presence and the bakery’s history.

“It certainly drums up interest,” says Pamela Wolfe, an estate agent with The Corcoran Group, though she did not feel the archaeological find added much value. “Manhattanites are very pragmatic about space. If it was a useful space it would have value but otherwise not really,” she adds. However, some archaeological artefacts are more valuable than others. The 16th-century frescoes discovered in Palazzo Bardi in Florence added about €200,000-€300,000 to the price of the property. “About the same as the cost of renovating them,” Thomson says.