How to avoid the pitfalls of building down.
In early November last year, the residents of Durham Place, London, which looks over Burton Court and the Royal Hospital in Chelsea, had a rude awakening when a house there collapsed, luckily injuring no one.
Social media (not to mention the printed media) was on fire the following day with ‘told you so’ comments directed at basements, the only real shared hatred in the smarter areas of London. Hated, that is, by everyone except those who have built one themselves. There was one problem with the story: it wasn’t true. There were building works going on, but no basement being excavated. The more prosaic truth probably lay somewhere between an unlucky builder and a poorly built house, but it was a good excuse to have a go at so-called ‘iceberg houses’, where there is more below ground than above, and where neighbours have to suffer months of noise, vibration, mud and lorries so that their excavating owners can enjoy their pool, games room, cinema or wine cellar and also, incidentally, make some money.
Some of these excavations have achieved legendary, or maybe that should be infamous, status, the truly egregious one being the so-called ‘black hole of Brompton’; a veritable meteor strike in one of the fan-shaped gardens at the end of Brompton Square where the convicted mortgage fraudster, Achilleas Kallakis, had permission to go down four floors (that is correct) and tried to go down further before he was stopped. It was quite a sight.
The so-called ‘basement blight’ is, in fact, something of a first-world problem, as the economics only make sense where values are very high. If it costs you £1,000 per square foot to excavate and the going value of the house on top is somewhere near that, then clearly only a masochist will go ahead: it’s cheaper to buy a new house, and you get to keep your hair and sanity. But where values are north of £2,500 per square foot, the equation is compelling: indeed, these days, it is probably the only way an owner can really add to the value of their house, especially where the house has no existing basement/lower ground floor/cellar. You can see this logic in action in Ilchester Place, a street of fine 20th-century houses abutting Holland Park, where there are currently six excavations going on at the same time. There are two main holes (no pun intended) in this attractive equation. The first is that amateur developers nearly always spend too much and underestimate the potential collateral damage to their neighbours. The second is that they make the error of thinking that the new space is worth the same as their first-floor drawing room looking over a leafy square, which of course it isn’t. It might still be profitable, but not nearly as profitable as the headline numbers would imply.
The high summer of basements is, anyway, now behind us, as within the past five years both RBKC and Westminster have put restrictions on what can be attempted. Both have similar rules: you can now only go down one more level than any existing below-ground space and only underneath an existing basement that predates 1948 in the case of RBKC. Listed houses are excluded and you are restricted to digging out to under 50% of the garden front and back. No more iceberg houses.
Despite these restrictions, a walk around residential central London would suggest that basements are still something that owners want to attempt. What should anyone contemplating a major project like this need to know and what are the potential hazards?
“Spring Street in Paddington and Bayswater itself are indications that if you go too far down you will find yourself in a watercourse”
The main one is geology. What is often not appreciated is that London is built over streams and rivers. Some of the street names give a clue. The river Bourne flows into the Serpentine, where it is dammed to form a lake. Westbourne and Eastbourne streets, and Spring Street in Paddington and Bayswater itself are indications that if you go too far down you will find yourself in a watercourse and your basement will be less of a digging exercise and more one of creating a waterproof tank. Trees and basements don’t go happily together, and the root systems of mature plane trees can stretch a long way. There is also the problem of waste water, of all textures, that has to be pumped from maybe 20ft down into the sewage system that is just below street level. What could possibly go wrong?
Though the theory of excavation may seem crude, the reality is that there are very few contractors who are really up to the job. It is a relatively new specialisation that has emerged with the surge in London house prices over the past 15 years. The big differentiation in the necessary skills is in having a deep understanding of the relationship between the house under excavation and its neighbours. Many of the houses in question were built during the housing boom that predated 1880 and the developers then – and this was before strict building regulations – cut corners and often economised on what couldn’t be seen, like foundations. The problem is that if you introduce a rigid box to contain your new basement, you restrict the natural movement of the houses either side and neighbours tend not to be too happy when their new kitchen moves and cracks appear in their walls. A really experienced contractor is going to be of more benefit than the most qualified structural engineer.
Something that often doesn’t get considered is the knock-on effect on the rest of the house. When you build your new media and utility room, what happens to the space where that used to be? And will the gleaming new area below ground make the rest of the house look rather dowdy and make you want to rebuild that too? Generally, unless it fits in with the flow of the rest of the house, a basement isn’t that useful and if there is no natural light, it probably won’t get used much. Also, the potential for a basement can lead to overvaluation. Sellers, who may have spent a small fortune on planning and architects’ fees on the assumption that it added great value to their house have, more often than not, found that it didn’t work out that way.
So is it all worth it? Yes, but anyone contemplating a basement, even a small one, needs to be aware of the pitfalls. Knocking on doors in the street of those who have undertaken one will yield invaluable local knowledge about what you can’t see. Being realistic about the added value may stop you doing it in the first place. And an experienced contractor will save both money and aggravation. Robin Williams once said that you should never economise on either sushi or plastic surgery. He should probably have added basement contractors to that list.
