Building Regulations Approved Document K specifies the following minimum barrier heights in England and Wales: 900mm for internal stairs (measured vertically from the pitch line of the stair); 1000mm for internal landings, mezzanine floors and internal balconies in residential dwellings; and 1100mm for external balconies, roof terraces and all commercial applications. Scotland (Technical Handbook) and Northern Ireland have their own requirements that broadly align with Approved Document K but should be checked independently. The height is measured from the finished floor level to the top of the handrail or the top of the barrier, whichever is higher.
