Goalpost vs single lintel

[Erik79]

Hi everyone as a bit of background we want to join 2 rooms on the ground floor of our property by opening up one of the walls. Overall the building is 4 storeys split into 2 different properties (build around 1875 on clay soil). Had the structural engineer coming in a few weeks ago and originally asked him to make a plan that completely removes the existing wall so there is a seamless transition between the 2 rooms. He suggested to replace the existing wall with a steel goal post on top of new concrete pads which is more invasive and expensive that we thought originally. After he send the calculations through we discovered that the wall that we want to open is actually not aligned to the rest of the walls on the next 3 stories above (it has a 20cm or so offset). We asked him to come back for a second opinion and also asked him to run calculations that will allow us to keep part of the existing wall (maybe if we keep 50cm or so on each side of the existing wall and we just make the opening smaller, between 1.5-2meters). We were hoping that in this case we wouldn't need a goalpost and the concrete pads and just a lintel will suffice.

SE came back to say that this is not possible now because of the off set and the new support needs to be aligned with the rest of the walls above and eliminate the offset that exists for the last 150 years or so...I dont want to go against the science here but what am I missing? Does it make sense to 'correct' in retrospect the original plan of the house? We also dont want to go through all the extra trouble (and cost) that comes with installing the goalpost and the cement pads if by making the opening smaller will allow just a lintel to take the load. The wall we want to open is between the bathroom and the dining room and is marked with red in the image below.
This kind of secondary consideration but the house is build on clay soil and high risk for subsidence but not entirely sure that adding a steel goalpost and concrete pads will actually make the risk less given that the rest of the foundations will still be on the soil. We are planning to get a second opinion from another SE but would appreciate peoples views on this. 

[George]

Assuming the 200mm offset means that the wall above is support on joists which are supported by the wall, then a lintel probably wouldn't be suitable. This is because lintels shouldn't be used to carry point loads without distributing masonry above. However a steel beam could be used.

 

Lateral stability is another big reason to use goalposts and without one I'd be looking to leave at least 600mm return of the existing wall (just above 'A').

 

There are also construction challenges with this although that's not strictly the SE's remit. 

Edited February 2, 2023 by George

[markc]

As above, a lintel is not the answer, a beam yes, no idea why the SE is saying it must be aligned with above. The existing wall has obviously worked for many years. Keeping some of the existing wall is easier but you then increase the load locally on the foundations which can cause the clay the be compressed - hence the goal post on new pads. Had this been a bungalow then no problem but the floors above make getting this right very important

[Erik79]

I decided to buy the bullet and go for the goal post. lifted he floorboards today to look at the condition of the subfloor before proceeding with the goal post installation. There needs to be a 120x120cm concrete base on each end, flash with the wall. The concrete base needs to extend 50cm past the external wall (and equally where the other end meets the internal wall). This means that it needs to go past the existing masonry foundations. Does anyone has experience on what is considered best practice in this case? Do they need to go underneath the existing foundations or replace them? I am spooked by the various experiences with tradespeople and this is one of the tasks that we really need to get right.
Second photo shows the subfloor next to the external wall (masonry footings).

[markc]

Dig a test hole against the existing founds down to desired depth, if the existing go full depth then you will (should) be able to leave the existing in place and put starter bars in to tie new and existing together. Good chance the existing founds and quite shallow so measure the depth and give this and a pic or two onto the SE for suggestions, hopefully you don’t need to go under as this is a pain to do.