Digging deep

From the road, the house looks like a bungalow. This is because it stands on a stretch of ground that slopes steeply away to the west. What you can’t see from the road is a dry moat that stands between the house, and a retaining wall that runs the house’s length. To the right is a slab that crosses from the retaining wall to the house, creating an undercroft beneath:

IMG_0551

To build the new extension, new foundations need to be laid. When the builders started digging, they discovered how the retaining wall had been built back in the 1960s. Essentially, all the ground nearest the road had been excavated, so that the wall could be built as a standalone structure. When complete, the excavated earth was reinstated against the wall.

The wall has done its job admirably for nearly 50 years. But because of how it was built, up-slope is a mass of ‘disturbed ground’. Building Regulations require foundations to be built on ‘undisturbed ground’. Unfortunately, this has proved to be quite elusive…

At 2.2 metres, the team struck gold (or so they thought) – undisturbed ground;
Chris & Katie 9-7-14 (31)

This proved to be deep enough for most of the walls and the foundations have been laid;
Chris & Katie 16-7-14 001 (10)

But for the foundation under the front door overhang, things were a little more complicated. To begin with, the second of the house’s two oil tanks needed to be removed;
Chris & Katie 16-7-14 001 (6)

It turned out the excavator wasn’t up to the task – so a bigger crane was needed;
Chris & Katie 16-7-14 001 (14)

With the oil tank gone, the team were feeling optimistic that at 2 metres, the depth of the empty pit would mean their excavations were nearly at end (a reasonable assumption given we’re only putting up a single storey timber-framed structure);
Chris & Katie 16-7-14 001 (15)

Unfortunately this was not to be, as the ground beneath the oil tank is also disturbed. Building Control have said the only acceptable method of digging foundations is to get to the underside of the retaining wall footing, maybe another 1.2 metres of digging.

So, we were presented with two options:

1. Keep digging to maybe 3.2 metres (we didn’t like this given the risk of compromising the integrity of the retaining wall)
2. Install pilings instead (we didn’t like this because they’d cost 2k each and we’d need four)

Both options seemed like overkill for a stretch of foundation that will only support 30cm of internal space and a 1 metre doorstep!! So, we’re going to reduce the size of the internal space by 30 cm and avoid the need for the foundation.

A frustrating week, but hopefully we go into week four with a clear plan for overcoming this latest challenge…

One Comment

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  1. Mrs Upside Down House July 19, 2014 — 6:19 pm

    A bit of a full on week for me! Having to liase with the builders and then tell Chris the bad news :/
    Let’s hope that the engineer says it’s ok to build on the retaining wall otherwise my lovely ovens & utility and Chris’s ceiling speakers may be at risk……….

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