Size beam required to support stud wall?

Hi all,

I'm planning on surrounding my landing with a stud wall (replacing what was a banister).

If I were to build straight off the existing outer joist (below where the previous banister sat), I would not meet the 900mm minimum width required for building regs.
The width of that section of floor is currently just over the 900mm requirement (without a banister). Therefore the stud wall would need to be built up off some sort of support that would sit directly next to the existing outer joist.

I'm obviously going to have a professional carry out the work, however I'd just like an idea of what size beam I would require in order to safely carry the load of the stud wall.
The stud wall would be 2.4m high, 2.4m long, it would consist of acoustic plasterboard on each side and would be filled with Rockwool 50mm insulation.
The wall to wall measurement that the beam would have to span is 10.5 meters.

I've done some research and it looks like I'll probably need a 6" x 6" beam, but as I'm not a structural engineer, I figured I'd ask in here in case some of you know how to calculate this stuff.

I've attached a picture showing where the beam would theoretically be positioned.
About 1/4 of the beam's length would sit directly below a ceiling (which as you can see if already fully supported).

Cheers,
Andy

 

I've just had another idea...
Would it be better to just use a joist hanger and hang an extra joist off one of the landing joists that run perpendicular to the joist that would support the stud wall.
Please see the attached picture to see what I mean

 

There is no minimum width for B regs.

 

I'm going off this...

(6) Internal doorways and hallways
Principle: Enable convenient movement in hallways and through doorways.

Criterion (6) Internal doorways and hallways
Movement in hallways and through doorways should be as convenient to the widest range of people, including those using mobility aids or wheelchairs, and those moving furniture or other objects. As a general principle, narrower hallways and landings will need wider doorways in their side walls. The width of doorways and hallways should conform to the specification below.


Required Specification for Criterion 6
Hallway widths
Subject to provision of adequate door opening widths (as detailed in the table below), the minimum width of any hallway/landing in a dwelling is 900mm. This may reduce to 750mm at ‘pinch points’ (e.g. beside a radiator) as long as the reduced width is not opposite, or adjacent to, a doorway. The minimum width of any hallway/corridor/landing within a communal area is 1200mm, which may reduce to 1050mm at ‘pinch points’ (e.g. due to a structural column) as long as the reduced width is not opposite, or adjacent to, a doorway.

 

Pretty sure the landing width is unlikely to be a BR issue given it’s still wider than a doorway and sounds like it’s almost 900 anyway

 

That stuff is only guidance.
Would anyone be using a wheelchair on a first floor landing. If that was the case, presumably they'd also need a stairlift to get up and down?