12 Jun 2014

Digging deep


Each issue i-build follows Will Anderson on his self-build journey. This month, the weather turns sour as Will begins his groundworks.



May seemed like the ideal month to start building our Arts and Crafts ecohouse in South London. The spring had come early, the ground was dry and there was plenty of daylight in all the hours that builders like to work. The sun shone for a week while the cheerful team from Premier Piling & Foundations drilled and filled the reinforced piles that will hold up our house and keep our slab away from the heaving London clay.

A slab on piles is not the most ecological approach to building foundations, given how much concrete has to be poured, but our ground is tricky and this design is the best way of ensuring that the building has a long-term future, regardless of what the clay decides to do. I had hoped that we would be able to cut the carbon by using Cemfree, a new product that claims to be ‘the sustainable alternative to concrete’, but unfortunately it’s so new the company couldn’t deliver it in our area. So it was back to good old concrete.

The piling went perfectly. You never quite know what you’re going to hit when you start drilling on a ‘brownfield’ site but thankfully the augur drill extracted nothing other than a variety of colourful clays. I grabbed and bagged some of this clay before it hit the skip. I know from old maps of the area that the houses around us are built on what were once brick fields. In fact some of the houses were probably constructed from bricks that were made from the ground that the houses now stand on. So, I’ve signed up for a ceramics course at Morley College in South London where I have so far established that my clay is indeed good stuff. It’s very pure, so does not need to be washed, and fires to a rich terracotta red. Perfect for indoor tiles.

Back on site, the sun disappeared and the heavens opened just when we started properly digging. The first hole to be dug, in what will eventually be our back garden, was – appropriately – a 1500 litre rainwater tank from Rainwater Harvesting Ltd. This is where all the water from our future roof will end up, so I should be able to keep my intensively planted garden well watered without using expensive and high-carbon mains water, especially in water-stressed London in mid-summer. However, when it first went into its hole the tank ended up floating in rainwater rather than storing it. Not a pretty sight.

As the rain really started to pelt down, the team began work on the main event: the broad hole for the slab and the subfloor of the house. This was a remarkably deep hole. I even wondered if the team had misread the drawings and had started digging a basement. But it was only what our super-insulated design required. When, in time, I stand looking out of the back window at the garden beyond, I will be standing on 20mm of reclaimed African hardwood, 25mm of screed in which underfloor heating pipes will run, a whopping 300mm of high performance insulation, another 300mm of reinforced concrete slab and finally 225mm of polystyrene heave protection. That adds up to a depth of 870mm and an awful lot of muck to be got rid of.

It all began to look seriously messy: the hole filled with water, the digger’s bucket got clogged and the dumper started sinking in the mud. But that’s the nature of building: you’ve got to take the rough with the smooth. It all got sorted out. Premier got a bigger digger in, the team gritted their teeth and, eventually, the hole was dug, the rain stopped and the sun came back out again.

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