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Building surveyors, London Clay and subsidence

05 April, 2017

As property owners and professionals, we’re used to change in building and property. A residential property built a century ago is now a stylish office for a professional services business, or a house of multi-occupancy packed with students. And of course, in March 2017, the Government’s triggering of Article 50 set Brexit in motion. Who knows what changes this will (or won’t bring) for property owners and building services in London.

Momentous though changes such as Brexit are, they take place over a few years, a couple of decades or maybe a century or two. But what about changes that take place over millions of years? And how the way we occupy our little corner of the earth today is influenced by things determined by the massive forces of nature 50 or 60 million years ago?

The challenge of London Clay derived soils

We’re talking about London Clay, the bluish Ypresian formation from the Lower Eocene Epoch, which underlies much of Southeast England. Because we’ve now built one of the world’s biggest, busiest and most important metropolises on this geological substructure, we now have to deal with the consequences. And those, as any chartered surveyor in London will quickly tell you, often appear as subsidence and related structural problems.

Every year, these problems cause heartache for owners, or prospective owners, of property in Greater London. Housing in London 2015 gives the total number of dwellings in London as 3,383,030. Some estimates put the number of London properties affected by subsidence as high as 1 in 50. As experienced chartered surveyors in London, we wouldn’t argue with that.

Based on this and the numbers in the2015 report, a staggering 67660 London dwellings could be affected. Maybe you’ve seen summer cracking as soil dries out and shrinks, or experienced the heaviness of the soil in winter while working on your London garden or allotment. (Or maybe you’ve noticed new cracking in the walls of your property, in which case you really should contact a firm of experienced London surveyors.)

Keeping building surveyors in London busy

So why is the London Clay that was laid down so many million years ago such a problem? And why does it keep London’s property surveyprs so busy? The answer lies in the fact that soils derived from London Clay are extremely susceptible to shrinkage. That’s due to the changes in volume that can occur as the soil’s moisture content changes. In fact, they present the highest shrink-swell hazard in the UK – and that means the highest potential for subsidence.

See what the British Geological Survey says

If you want further information, visit the British Geological Survey website where BGS Geo-Sure depict the incidence of this kind of hazard on a very revealing map. All that dark blue isn’t a pretty sight – as the Cambridge Boat Race crew know too well from the annual Boat Race from Putney to Chiswick on London’s River Thames!

There’s another factor that London chartered surveyors are all too aware of. It’s the particular vulnerability of London’s Edwardian and Victorian housing stock. Why? Because of the very shallow foundations used when these properties were built. If you’re planning to buy in North London, where these properties are ubiquitous, you’ll want to be aware of the issues and appoint a surveyor who knows these properties intimately. Even if buying elsewhere in Greater London and the Home Counties you should be on the alert for subsidence – especially if you notice telltale signs of cracking in a property. The key message is that, regardless of whether the property has a NW London, North London or West London address, caveat emptor applies as ever. You would be amazed how often a building survey in London reveals actual or potential subsidence problems.

How experienced London surveyors can help you

That’s where experienced property surveyors with London experience come into their own and earn their remarkably modest fees. Of course, an RICS surveyor from ‘granite territory’ such as South West England should understand the principles. But if you’re buying in Town, why wouldn’t you entrust your survey to a chartered surveyor in London?

Look at it another way: if you decide to treat yourself to a classic Porsche or Bentley, would you entrust its assessment to a (generally very capable) garage that isn’t familiar with such marques? Can you see our point?

Local knowledge counts

When you entrust your London property survey to an RICS London surveyor, you have everything to gain from appointing one that knows local property inside out. Why wouldn’t you hire surveyors in London who know the property, the district and the potential problems where you’re looking to buy? What could beat a professional ‘on the patch’ who has decades of experience with the unique challenges and problems of London property – including the shrink-swell issues associated with London Clay soils? Building surveyors in London have that expertise.

As well as alerting you to potentially serious problems, a skilled London surveyor may be able to reassure you that minor cracks aren’t due to clay-related movement. Other causes may be at work: vibration; local traffic movement; normal settlement (as distinct from subsidence) in a new property; or an easily fixed problem related to the water demand of a carelessly planted tree – poplars are notorious.

The key to saving money and priceless peace of mind

Often, a surveyor’s advice will enable you to take simple remedial action (or negotiate a price reduction) and proceed with peace of mind. And if you’re planning to sell, they can enable remedial measures to be put in place before the property goes on the market so you can sell with confidence.

In extreme cases, that professional opinion will enable you to walk away from a potential money-pit. Such advice is priceless for your bank-balance and peace of mind. Suddenly, that modest investment in a full structural survey by a building surveyor from London looks like extremely good value.

That’s because it is!

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