waterproof guarantee basement construction build manage
  waterproof guarantee basement construction build manage
 

We appeared on Grand Designs on October 25th 2017.

new basement on a small plot in east london

In the preview the week before, Kevin McLoud looked down our excavation and said "Shambolic".

He was quite right. So how did we get to a situation that looked so bad?

The basement was to be about 9m by 4.5m on a plot the same size, though a bit of the road the far side was borrowed for storage.

If the excavation was piled first, then there would not be enough space to make the new house large enough to meet the Standard. We had to agree to excavate and build without any prior support to the ground.


The London Housing Standard for a 2 bed 4 person home is 83m².

If you do the maths, 9m x 4.5m less 300mm for walls equals 32.75.

83 divided by 32.75 is 2.53 floors. But to include stairs you need 3 whole floors. You need outdoor amenity space as well.

new basement on a small plot in east london
new basement on a small plot in east london


Joe, the client, a qualified designer and at that time the project manager on another building project, devised a house with exactly enough internal floor space and an outside roof terrace with a view of the rooftop lawn.

But the basement retaining walls could only be 200mm thick.



He found a structural engineer, who carried out his own soil investigation.

But the engineer only investigated down to 3m.
waterproof basement construction


The engineer told us dig out half, build half and connect the second half with lacer bars. The excavated sides of each half would be stable.

waterproof basement construction

Then he produced drawings telling us to excavate 3.5m

waterproof basement construction

In that extra half metre everything changed, which Grand Designs showed with a close up in the episode.

waterproof basement construction

  1.   The soil turned to silt, typical of the silt that overlies London Clay.

  2.   All the water sitting at the bottom of the gravel that could flow into our excavation flowed into our excavation.

  3.   The water washed the silt out from beneath the gravel, and

  4.   the gravel sides kept falling in.
Even though we tried to build the basement in quarters the sides collapsed many times.

basement piling basement support basement formwork

So, basically, we were given a method statement to price and follow and it did not work.

We were not supposed to find any water, but when you do you can see what happens in this 19 second video.

We were told that we couldn't use steel sheet piles or trench sheets. We were not allowed to use anything else we suggested to stabilise the ground either, such as resin injection or a cement render to the natural ballast.

It was horrible.

The client wasn't in the least bit sympathetic saying that if his engineer agreed with me (that his engineer had made a huge error) there might be something to discuss. But there wasn't likely to be any more money and I had agreed a fixed price.

I continued until I thought that the site was safe.

Formwork designed for 240mm thick walls gave way with concrete up to 800mm thick because it had to be rushed so we could pour before another cave in.

But despite my being very frightened for a number of weeks no one was hurt.

Given the circumstances, I am proud of that.


After that Grand Designs preview, I sent a text to the director who replied "We've been very careful not to appropriate blame. I think it comes over as unfortunate and not funded very well ... you were given an impossible task ... and you gave it a good go."
the 3 dots ... are quoted, this quote is complete.

I wrote to the producers to complain that whilst they were fair many viewers were jumping to the conclusion that I had foolishly chosen not to support the sides of the excavation.

Here is their answer in full. I have added some highlighting.

Grand Designs Basement Expert Phil Sacre Grand Designs Basement Expert Phil Sacre


With the plot being so small that meant that the retaining walls could only come in 240mm from the boundary. The engineer thought he found a way to build the walls without supporting the sides of the excavation.

In the programme it was said that the basement structure cost £80,000.

The contractors that replaced us were allowed to drive sheet piles down through neighbour's land. We weren't.

Joe said to camera he was disappointed he had paid in advance for work not to spec. But the work was priced against the data he supplied, not what was found to be the case.

He would not pay us a penny more for the difficulties.

Yet it could not be fair that we paid for the difficulties his engineer failed to identify.

Of the £80,000 it was said the basement structure cost, for almost all the excavation and muckaway, an end wall and almost 75% the length, we got paid £28,845.

The new contractor seemingly finished it with almost twice the money we received for the bulk of the structure.

Joe and Lena are a lovely couple and I am pleased they saw the project through.


We have continued to accept some very difficult work since but we insist on a more thorough soil investigation than was carried out here.