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To be honest, I'm glossing over some details somewhat! For example, that 45-degree wall was interesting to brace, mainly because it wasn't exactly 45 degrees. After foaming the wall joints, I was wondering how to brace the wall properly. My builder-come-consultant had a genius idea. We ended up creating a hinged OSB screen (using a bunch of standard door hinges), so that we could form each of the angles independently. Then we screwed the OSB to the webs in the ICF blocks to make it solid. Then we put CLS timbers across the OSB, and bolted together, to give it more rigidity, and bolted the CLS timbers together. Worked a treat. You can see the detail in pictures 4 & 7 above. Lifting the steel beam was a challenge, too. We attached ratchet straps around the uprights for the scaffold system (one in the kitchen side and one in the garage side, and clamped into the web with timbers), and then used spare ICF blocks from the basement walls as chocks to insert every time we got another 400mm up. That allowed us to adjust the straps safely each time, and start again. The problem came when we got to the last block - one ratchet snapped, and the beam dropped at the back. Thankfully we were (sensibly) working from above (on the scaffold) at that point, because if it had hit someone below we'd have needed an ambulance. The final 700mm of lifting for the back end of the beam was done by myself and 2 mates on our shoulders, once we had lifted the front end onto the garage wall and secured with metal strapping so it couldn't fall off. And boy, was it heavy! Now that I am getting a bit of personal time back, I'll start trying to include more anecdotes like these in the blog - it's just been mental levels of stress the past few weeks (Dad in hospital 200 miles away, and my day job looking like it's about to end right when both mortgages are at their peaks...)

That's the point - we had a topo done (cost £420) prior to completing the excavation of the basement hole - all setting out was then done by a setting out engineer (at a cost of £350) based off the topo. They just misread the topo somehow, because our only height datum was the DPC on the neighbour's house, and all the measurements were calculated using that as ground level (when clearly it wasn't). By the time we realised the problem, we had concreted the ground floor walls and built the first floor walls up. Our choice was either to have lower ceilings on the first floor (and I am not a fan of low ceilings - the basement is over 9' and we're at 8'4" on the ground floor), alter the roof pitch, or get the planners to let us have a taller house than either side. I vetoed option [1], and we had had enough dealings with the planning dept at this point to know option [3] was unlikely, which only left option [2] - alter the roof pitch. It still required a new planning application, but because it was obvious why we were making the change, and because it was obvious we weren't trying to make space for a future loft conversion (it's only 1.4m clearance in the loft now), the planners were much more accommodating.

Assuming a passive slab was planned from the start, 900mm seems an awful lot to be digging down, even if clay was a possibility. Please don't think we're having a go here, by the way. It's just that someone may read this in the future looking for information, and it will be helpful for them to understand how this all happened (and how to avoid it!)