A few months ago I read with horror about a house collapse in North London. The family concerned were extending their ground floor flat with a basement. Everything seemed to be going well until one day their property and the one above ended up in the freshly excavated foundation.
For renovators tackling structural changes this story is the stuff of nightmares. It was at the back of my mind as I went to meet, George, our structural engineer.
The preliminary plans agreed with our architect provided the framework for the engineer’s survey. George’s job was to assess the proposals, calculate the number and size of steel beams needed and draw up engineering plans. The plans set out where the beams should be placed and fixed together.
George laid out the architectural plans on the kitchen work-top and we talked through the proposals. (Click here for more information in last month’s post.)
We are making two structural changes: a loft conversion and the removal of an internal wall on the ground floor. George had no concerns or issues with the loft conversion. Our plans are straight forward.
The ground floor changes were a different matter. We spent a considerable amount of time discussing the structural impact of the proposals.
Our architect had explained that we could replace the wall with a steel beam and supporting central pillar. This would mean no foundation works. George agreed that was possible but some foundation work would still be needed. The diagram below demonstrates the issues we faced.
Our choice was to pay for a central pillar and foundation works to that point, or simply pay for foundation works end to end. There was no getting around the ground-works. This diagram explains the issues further.
The decision was easy. We decided to go for the ground-works with a fully open space. A central pillar wasn’t going to save us any money so there seemed to be little point in creating this obstruction.