Load bearing capacity timber internal wall?

[Builder2011]

Good afternoon.

What is the load bearing capacity of a first floor internal timber frame dividing wall in a Victorian mid terraced building on ground and first floor? The building is approximately 7m from front to rear and 4.6m across from party wall to party wall.

The dividing wall is approximately 3.5m in from the front of the building. It is formed from 4" x 4" pillars with 380mm spacing centre to centre. The top of the dividing wall is a 4.6m 4" x 4" beam between the party walls which in turn supports the internal ends of 3.6m rafters coming from the front of the building and 4.2m rafters coming from the rear of the building.

The proposal is to fit new loft joists between the existing loft joists (or adjacent to the existing loft joists) and to fit boards on the new joists to make a floor. The new joists weigh 204 kg. The boards weigh 413 kg. Dust and dirt removed weighed 47kg. There would then be carpet. There is an existing water tank.

Allowing for the dirt removed, there would be additional structural load of c.570kg (or 617kg total joists and flooring boards).

Does the dividing wall have adequate load bearing capacity for its share of the additional structural load? If not, how many timber pillars should be added to provide adequate load bearing capacity? (Removing the wall and putting in an RSJ is an option however the loft is for storage, not a habitable room.)