hi all,happy new year ,i have been asked by the other half to renew the kitchen and knock through into the dining room to make it all into one room,i have a solid single brick wall between the 2 rooms and a bedroom and bathroom above,all walls upstairs are stud walls.the stairs go up the middle of the house from side to side and joists run side of house to side of house resting on dividing wall.the stairway wall that is connected to the dividing wall is studwork. my question is,,how much of the solid dividing wall do i need to leave (stair end) to support the rsj ,the other end i believe i can rest on the inner skin of the exterior wall of the house,ie 100mm so that end sits just into the cavity.is this correct? the rsj would be approx 10ft long