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:
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…
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);
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…