Slip-Slidin’ Away

Serena asks:

We are in the process of purchasing a 1900 Victorian terraced house in the Westcombe park station area and was just told that the house was previously underpinned due to subsidence (a cracked sewage pipe beneath the house).

Is subsidence in a common issue in East Greenwich area or Greenwich as a whole?

The Phantom replies:

I get asked this so often I should probably put it in the FAQs – but the very fact that I do probably answers your question, Serena.

Yes, subsidence is very common in Greenwich, East Greenwich and Charlton. Basically the Victorian builders hadn’t read their bibles properly – they built their houses on what’s known as Thanet Sand. It’s generally fine – it settles after building and then stays where it is, as the hundreds of 100 years-and-counting houses still in remarkably good nick testify – but if something untoward happens – a burst water main, for example, or in your case a cracked pipe, the sands start shifting again.

Generally underpinning isn’t required. Once the cause of the issue is fixed, the sand settles again (we’re not talking fine, golden,┬ádesert-island stuff, we’re talking gritty, as-sand-goes-stable gravel that WANTS to stay pretty still), the building’s cracks are filled and the whole thing is good for another 100 years.

Perhaps your house’s previous owners went for the belt-and braces approach – if it’s underpinned it definitely won’t happen again.

The other good news is that you won’t suffer from the other subsidence-causing problem – ┬átree roots. This usually happens in clay soils where the roots expand the clay, the clay sets, then when the roots die, the clay collapses. There is some clay in Greenwich but it’s in pockets.

There’s a fun little booklet for kids and Phantoms that describes the geology of Greenwich’s soil, called Holiday Geology Greenwich.’.I got my copy years ago from the tourist centre and highly recommend it if you want to know about the Greenwich Fault Line (no, really), which fossils can be found in the stone at the Old Royal Naval College and the days when dinosaurs roamed the Peninsula.

the attachments to this post:

holiday geology
holiday geology

One Comment to “Slip-Slidin’ Away”

  1. tallgables says:

    We recently purchased a similar property in the same area that had been underpinned due to a collapsed drain. We ordered the most extensive survey and got a drain company to do a CCTV report. It certainly set our minds at rest.