I had this done following moving into our new house around 2 years ago – the section of wall was around 10ft in length.
I don’t believe that the builder I employed gained any building approval from the local council for the work.
The builder explained that there were two options, the cheaper where the RSJ would rest on supports at either end. The disadvantage with this method is that it leaves the RSJ on the ceiling where the wall was – making it clear that a supporting wall had been removed.
I opted for the more expensive solution where the RSJ is embedded in the ceiling at the same level as the existing joists. This is achieved by cutting a section of the joists to allow the RSJ to be placed in position; then solid blocks wood are bolted on to the cut joists and RSJ – fitting into the indent section of the RSJ, thereby supporting the joists.
Even though the builder explained the above to me – I could not visualise it until I saw the work being done.
But the extra cost is worth it – with the entire kitchen ceiling being flat, rather than having a box section enclosing the supporting RSJ.