Structural Engineer query

[user1466090222]

Hi just wondered if anyone out there can help. We are having a first floor extension built over an single story room to create 2 new bedrooms and a bathroom. The existing room is built of thermalite blocks and the new first floor is a wooden construction. We engaged a structural engineer to work out the calculations - I was concerned that the thermalite blocks may not be as strong as ordinary concrete blocks - he said that all should be fine. We asked if he wanted to look at anything else like floors/ceilings/joists etc but he said no. Now we have had a problem in that the roof structure wasn't right when the builder built it, and we have incurred extra costs for labour. The SE says that our builder should not have been following the drawings as they weren't to scale (?). Surely that is what we employed him for. I am now getting really jittery about whether the foundations are strong enough to cope with the weight of the building - and he didn't check these. Can anyone advise?

It's difficult to say without knowing exactly what you have enployed him for. Did you have architectural drawings and details? In general drawings should never be scaled from - if a dimension isn't there then they should ask. And if you are building on top of existing then the dimensions are probably determined by what is there and it would not normally be the structural engineer's job to do an accurate survey for the build.

You should have building control involvement who hopefully have reviewed the structural calculations. If you have any concerns I'd suggest asking them in the first instance.

We had the plans drawn up by a plan drawer rather than an architect. The floor has now been taken up and has revealed quite substantial blockwork/foundations underneath. The original room was added on to the back of the house by my parents when they lived there, and the original house is built on a slope. The foundations go down to original ground level which is about 6ft at its deepest, and now the builder has seen what is supporting the new rooms above then he seems happier. I however am less happy with the SE, as I had the architect detailed drawings for the room my father added along with SE calcs, and we offered these to our SE who said he didn't need them. My point is surely he owes us a duty of care in that he should make sure that his design is likely to hold up, especially if it is being added on to a single story building where the client has advised him of the structure, ie thermalite blocks, plus offered the original drawings and calcs for that structure. Is it not in his best interest to advise us, as clients, that he needs to check all this out? He did charge us £2k for doing the drawings and producing calculations.

By the way whatsthatcomingoverthehill, I am sorry I didn't respond sooner, I am new to Mumsnet and wasn't sure how to find the thread I started - lol!
As another note, we have totally lost confidence in the SE and we are now going to get the structure checked with another engineer.