The novelist Will Self doesn’t live in a rickety medieval garret with saggy floors and creaking timbers, but in a seemingly solid Victorian terraced house in Stockwell, south London. Yet one evening last month, Self and his neighbours, who include Edward Garnier, the solicitor general, were evacuated after a roof parapet at the front of the terrace collapsed, scattering bricks and tiles across the street. The lofts of four £1m houses were left open to the elements and the residents were banned from re-entering for days.
We know the roads are dangerous, and take care with gas and electricity, but one hazard of everyday life that we don’t tend to consider is our houses collapsing without warning or obvious cause. So just how safe are we inside our homes?
In the aftermath of the Stockwell incident, a Lambeth council inspector was quoted as having blaming the collapse on “diurnal shift” — sudden swings in temperature between night and day, perhaps exacerbated by the changeable spring weather.
A hazard that we don’t tend to consider is our homes collapsing without warning or obvious cause Yet buildings ought to be able to cope with the capital’s moderate climate. The collapse underlines the vulnerability of parapet walls, which are a feature of many Georgian and early-Victorian London houses. Such walls do not enjoy the protection of a roof, so rainwater can seep into the brickwork. When this freezes, it can open cracks that, with repeated freeze-thaw cycles, become wider and wider.
Like most house walls, a parapet relies for its structural rigidity on wooden beams that tie it into the general structure of the building. Gutters behind the walls can get blocked, leading to ingress of water that can’t be seen without getting onto the roof.
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“If you’ve got a parapet gutter that has been leaking for years and years, the timbers are going to rot and lose their structural strength,” says Matthew Slocombe, director of the Society for the Protection of Ancient Buildings.
Another possibility, according to Graham Ellis, associate director of the Royal Institution of Chartered Surveyors, is that the houses were never built properly all those years ago. “Looking at the photographs, the parapet wall seems to have sheared away from the party walls between the properties,” he says. “This has happened in four houses, in exactly the same way, which makes me wonder whether the party walls were properly tied into the outside wall.”
Such accidents are rare, but not unheard of: in June 2007, Hazel Blears, then chairman of the Labour party, had a narrow escape when the top two storeys of the building housing her offices on Dean Farrar Street, in Westminster, collapsed during renovation works. A Romanian worker was trapped in the rubble and later had his leg amputated. It transpired that the building was in the process of being converted into a hotel, but without planning permission or approval from Westminster council. A fortnight later, Blears became communities secretary, with ultimate responsibility for building regulation.
Unsurprisingly, disturbance to foundations is a common cause of building collapse. In 2003, a house on Lavender Street, in Stratford, east London, had to be demolished after work on the Channel tunnel rail link caused a large crater to open.
The previous year, an end-of-terrace house in Aldershot, Hampshire, collapsed after council works to remove trees and shrubs from an overgrown piece of land next door — the site of another property that had been taken down several years before. The end wall that collapsed had originally been built as a dividing wall between the two properties, and was never designed for the loads it ended up bearing.
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The popularity of basement extensions — especially, but not exclusively, in prime areas of the capital — has also led many owners to fear for the structural integrity of their homes — and not without reason. In 2008, a house on Trinity Road, in Tooting, southwest London, collapsed while the owners were attempting to burrow out below.
Done properly, such work begins with the underpinning of a building’s walls — effectively taking the foundations to a new depth below the level of the planned basement. In this case, however, the owners, who were fined £5,000, had started on the work without getting building approval.
It doesn’t always take such dramatic, visible alterations to cause a building to collapse. Often, the cause is obvious only once the collapse has exposed underlying weaknesses.
“There was a case involving an outside gable wall on a Victorian house in Southport,” Ellis says. “The house had cavity walls, which relied for their strength on the outside and inside walls being bound together with slate ties. Over the years, the walls had moved and the slate ties had snapped. Then, one windy night, the outside wall was sucked away.”
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Slocombe says that the collapse of old buildings is often down to alterations made by owners failing, through ignorance, to take into account how their houses were built.
“Many Georgian and Victorian houses have internal walls made from studwork,” he says. “They look insubstantial, and if you tap them they sound hollow, which leads people to think they are not structural and can be removed. But such walls often have an important bracing effect on a house.”
Many cottages built before the early 20th century have earth or “cob” walls made of blocks of mud and straw. Such walls will lose their strength if they are allowed to get too damp. Many homeowners erroneously think they are doing their homes a favour by painting the external walls with modern paints, but this has been known to lead to collapse — a waterproof coating can prevent the evaporation of moisture from the outside wall, leading to a loss of structural integrity.
Fortunately, nobody was injured by the collapse of Will Self’s parapet: it may even lead to a novel. It could also serve as a reminder to homeowners that walls are not always as solid as they seem.
Keep a roof over your head
• Ingress of water is a cause of many structural problems. Venture into the loft occasionally to check for signs of stained timbers, and clear out gutters regularly.
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• Understand how your home is constructed. This will help you to appreciate what holds it up and avoid using inappropriate modern techniques. As an example, before the 20th century, brick houses were built with lime mortar, which is flexible and allows a wall to move. Repointing with a modern cement mortar could lead to cracking. The Haynes Period Property Manual by Ian Rock (published on Friday at £22) explains how to maintain traditional building materials.
• Always take impartial advice from independent structural engineers before making alternations that could affect your home — don’t just fall for the sales patter of a damp-treatment company.
• Don’t worry about every crack. Almost all old houses have some cracking, and most of it is benign. Just look out for telltale signs of a serious structural crack, such as a stepped appearance that follows the course of the brickwork, or a gap that’s wide enough to push in a £1 coin.
• If you live in a listed property, it could pay to take action sooner rather than later. Until October 1 this year, improvement works on such buildings — but not minor repairs and maintenance, such as repointing brickwork — are exempt from Vat.