Typical and common foundation subsidence in a Victorian terrace outrigger.

What is subsidence?

Subsidence is when the soil below and around the foundation is compromised causing the foundation to drop/rotate/fail.

Typically this will result in diagonal cracks through masonry/render.

If you stand outside looking at the building and draw an imaginary arrow down through the centre of the crack this usually reveals the location of the problem.

Why is this?

This is because building cracks always form perpendicular to the line of stress. In this instance, the arrow points down towards a gully and buried drainage, which is fixed close to the building/foundation.

Another clue is sloping first floors. If they slope down in the same direction as the arrows towards buried drainage, it is obvious that the local drains must be exposed for inspection.

Here, we identified a crack at the connection of the gully spigot into the drain. Every time it rained, water escaped and, over many years, eroded the soil around the local foundation, causing it to drop.

These old Victorian and Edwardian terraces usually have shallow tapered brick foundations, as opposed to deep concrete strips, and so subsidence and settlement of the foundations is common.

The drain was repaired, and the corner of the outrigger was underpinned with a series of cast concrete block footings.

These are the kinds of issues that, if explained and reported correctly, can help you negotiate thousands of pounds off the price of your next house.

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