Feature stairs raise the points Building Control looks at hardest: open risers, gaps between balusters, handrail height on a gallery, headroom under a tie beam. The rise, the going, those heights and gaps, and the loadings all come from your architect or designer, agreed with Building Control.
We make the steel to their drawing and do not certify the result. If the stair hangs off an old wall or lands on a new floor, the calculation for that is your structural engineer's. If a slim section on the drawing looks too lively to us, we say so before it is made.
If the barn is listed, consent for the stair is yours to obtain. Tell us what has been approved.