Chimney breast removal.

Hello,
I intend to remove the chimney breast in an upstairs bedroom of my mid terraced house. The chimney backs on the next door.
becasue of the logistics I need a 4 mtr RSJ spliced. And my SE has given a size of 4 mrt spliced at the centre, bolted by two 650 x 10 x 100 plates in the H section, a 1000 x 90 x 10 plate bolted on top of the RSJ and a 650 x 90 x 10 plate bolted on the bottom. The size of RSJ given was a 152 x 89 x 16Kg. This is to support a chimney in the loft 3 mtrs above the RSJ, 1 mtr wide and 300 deep. There is also the roof purlin supported by the chimney on one end on corbelled out brickwork this is a 10in x3in x 4.5 mtr The RSJ is sitting on 220 x 150 padstones on the outside wall and an inside dividing bedroom wall.
The problem I have is that when the builder came to view he felt the RSJ was not "big enough" ie the 152 X 89
Could anyone offer advice as I do not wish at his stage to question the SE but the builder does have a lot of practical experiance.
Many thanks

Builders tend to beef things up to err on the edge of caution.

if you have calcs you have paid for from a reputable SE then he has to indemnify his work, so they will do the job, if anything was to fail the claim is on the SE.if it relates to the loading on the steel. this type of work is also notifiable to local authority who will also require a copy of the calcs and they have them checked out any way. so I would trust the SE thats his job.

Many thanks for your reply which is a reassuring, however I know if the beam fails I may have redress with the SE but if it goes in the night I will be sleeping under it!!! I think I will get a second opinion form a different SE TA

Owning a building company my self we have never had a set of calcs fail. as structual engineers will give an additional safety factor as well.

of course your other option would be to continue through the roof remove all the breast and chimney and make good to the roof

its not as hard as it sounds. as your starting at the top and working your way down, so you have no unsupported areas to worry about.

this is if the chimney that backs on to next door is not shared and only services your property.

Hello again,
Many thanks for reply and idea but it is a shared chimney. Going to speak to original SE and ask his thoughts.
Thanks again.