RSJ AND NO WIMPEY FINES

I wonder if the Structural Engineer came to your property. I would assume he would have been in contact with the builders to get the necessary data of the original build, in which case he will have all the necessary facts. What you need to remember is that there is a UDL uniformly distributed load whilst the existing wall is in existence, once you remove that, you are creating two point loads - one at either end of the (in your case) RSJ which is probably a UB....So if the calculations he has given you just refer to the load capability of the beam without site visit to ascertain the suitability of the wall to take the load, or without the necessary information on the type of foundation beneath the wall. I would assume the Engineers details will advise you that he has checked those necessary details, if not (maybe because he was only asked to calculate beam sizing) you should go back to him and ask for those details. Also maybe to check his credentials

When I have designed changes for these properties in the past, I have avoiding using the existing structure as load bearing and designed steel posts to support any knock through beams. The engineer is best qualified to justify this design they have given you. Just confirm with the engineer to make sure they are aware that this is a Wimpy no fines property. You need building control approval for this work, therefore asked building control as well if you’re not sure.