Callum Morrison, a 21-year-old carpenter from Croydon in south London, has spent his day working atop the 919-year-old roof of Lincoln Cathedral, repairing rotten rafters which have been eaten away by worms and deathwatch beetles, in a bid to preserve a piece of history. "Not many power tools here, just hard graft," he says, when he's finally able to come down off the roof and talk. "We need to replace the rafters in keeping with the original roof, to keep the rot at bay and keep the roof in working order. The last time this roof was worked on was hundreds of years ago, by someone with even fewer tools than I have now. And now I'm working on it – that's an incredible feeling."
But it's not only ancient cathedrals which need repairing. In 2008, English Heritage warned that the future of the country's old buildings, including more than five million homes, was at risk because of a severe skills shortage in traditional "heritage" building methods, including stonemasonry, glazing, lead working, joinery, plastering and carpentry (Morrison's specialist area). At one time, these skills would have been passed down through generations, but they now risk dying out because there aren't enough new entrants joining the specialist heritage trade. "An old or traditional building is typically one built before 1920," explains John Edwards, who is senior buildings surveyor in the conservation department at English Heritage.
"Of all the buildings which we classify as 'traditionally-built' in England, 90 per cent of them are people's homes, which is why it's so important to make sure they are looked after properly."
According to the most recent statistics from English Heritage, there are less than 30,000 properly qualified, skilled craftspeople, out of a workforce of 90,000 in the construction and building trade.
Over 60 per cent of repair jobs done on houses built pre-1920 are carried out by workmen who do not have the right skills or materials to work on traditionally-built homes – which is why there's now an urgent need to pass heritage building crafts on to future generations, or else risk millions of homes falling into disrepair.
"Unless we supplement the existing workforce with younger people before a generation goes into retirement, then we risk losing our traditional, English crafts, and we won't be able to repair our old homes," says Edwards. "We've got the oldest building stock in the western world and it needs to be maintained. This isn't just about preserving Georgian mansions, it's about preserving any traditional building. Our definition of a traditional building is one with solid walls, made with porous materials, built with stone and brick and bedded in lime mortar, so it applies just as much to an old Victorian terrace or a flat in a Victorian conversion as it does to a country estate."
Edwards says many homeowners often aren't aware of the specialist maintenance their property might require, which is why they end up consulting general builders rather than heritage ones.
"Listed buildings are protected, but we shouldn't forget all the unlisted properties that still require the same care. A Georgian mansion will get treated in the right way because of its Grade-listing, but a Victorian or Edwardian terrace or townhouse will end up getting treated by mainstream builders, who apply modern techniques and modern materials, like concrete, to old buildings," he says. "This inappropriate use of skills and materials in repairing old buildings leads to more problems which ends up being costly for the homeowner."
Morrison, who worked on maintaining period homes in London before his stint on Lincoln Cathedral, says that one of the worst mistakes made by builders – who aren't specialised in heritage skills, or indeed by extreme DIY enthusiasts – is to cover cracks in brickwork with concrete or cement, instead of using lime in the form of a wash, mortar or render, which gives natural protection against weathering. Lime needs to breathe, but if it gets covered with concrete, it no longer can, which leads to more cracking.
"When we say lime breathes, we mean it takes in air and water," Morrison says, who advises homeowners to seek specialist building craft advice on lime washing, rather than attempting it themselves. "Cement is our modern-day version, but it fails over time. You can lime wash your property every year in bad weather, but it all depends on the way in which your house is placed with respect to the weather and wind direction."
Similarly, the notion of a building "breathing" applies to timber-framed houses, too. Morrison explains that if you're doing a modern loft conversion in a pre-1920 property, you must ensure the timber has enough ventilation, or else it will dry out, leading to the homeowner's nightmare of dry rot. "If you smother the timber's air source, it'll crumble," he says.
Morrison is one of 12 apprentices on The Prince of Wales's building crafts apprentices programme, which aims to offer young people within the building crafts trade a chance to specialise as a "master craftsperson" with expertise in traditional building and construction skills. He hopes to work on repairing oak-framed homes next.
He says: "With old buildings, it's about working with care to deal with a problem in a way that respects the building's history. That's what restoring, repairing and conserving is. Even if your home isn't a listed building, it's important not to get too carried away and start changing the original details."
But even protected properties are at risk of losing the skills required to maintain them. The average age of the National Trust's 150 building contractors – employed to look after its tenanted homes as well as its big country piles – is over 50 and approaching retirement, which is why the Trust launched its own building apprenticeship scheme, aimed at 16 to 19-year-olds, last year.
Josh Dalton, 18, is one of them and is following in the footsteps of his grandfather, who worked as a carpenter. Dalton is training in general property maintenance for traditional houses, while also studying for a NVQ in carpentry. "I like being able to feel that I've worked on a bit of history," he says. "Even when I'm working in a small house, I'm still using old-fashioned skills and techniques, such as making joints myself and not relying on prefabricated ones."
But while there is a shortage of new entrants in the heritage building crafts sector, there is still considerable interest in it from young people – the National Trust says it received 200 applications for just one of the apprenticeship places advertised last year. Meanwhile, the Prince's Foundation, which runs the Prince of Wales's building craft apprenticeship, says it has seen a "real enthusiasm amidst young people to learn traditional crafts".
A Cambridge graduate in architecture, Nancy Peskett, deliberately changed her career path to take up stonemasonry, taking an advanced diploma in the skill at the Building Crafts College in East London. She is now coming up to the end of her apprenticeship on the Prince of Wales's building crafts programme.
"I wanted to do something that would use my hands and my brain," she says. "Stonemasonry is very logical and practical, but also creative." As a stonemason, Peskett repairs old homes where stonework has been damaged or broken by cutting stone (often by hand) and fixing it into place.
She says the biggest problem facing pre-1920 homes are cracks in the brickwork and external facades, since older buildings are especially susceptible to water and weather damage.
"Buildings move with age and when cracks begin to appear, you have to replace and repair them in a way which is not just aesthetic but also practical," Peskett explains. "It's important to replace cracked stone with similar natural material. A lot of people replace stone window ledges with concrete ones but that's just not compatible with an old building."
Replacing external stone window sills is one of the most common stonemasonry jobs for old homes, says Peskett – but there is also an aesthetic side to the job, as homeowners doing a restoration job often approach stonemasons to restore intricate stone carvings, usually found above doorways.
It's this part of the job that reminds her that she is working with homes which are part of history and which are so important to look after.
"Working with old buildings teaches you so much about the way every building, including modern ones, work. You learn about building materials, and about how a property can decay – and this is what you need to know in order to be able to build better buildings. It's literally like learning from history."
To find a specialist heritage builder, visit www.english-heritage.org.uk.
National Trust Building Apprenticeships, www.nationaltrust.org.uk.For the Prince's Foundation, visit www.princes-foundation.org