I'm pretty sure I know the answer but think there could be a grey area here? A Principal Contractor has provided welfare facilities in accordance with the current regs. they include portable cabins for messing with room for changing and hanging clothing and heating etc. A subby has now asked for an additional facility for changing clothes and drying. The work is entirely indoors and temperatures a few degrees more than outside. The work is not exactly strenuous and all hands wear PPE/RPE when required. Not hazardous materials just a little dirt. If the additional cabin is provided is it the PC who pays or can we ask the subby to provide it for themselves.

changing cloths and drying facilities should already have been accounted for in the tender as welfare is not just a 'sitting down to eat' exercise This is an area the CDMC etc should have identified before work starts and again risk assessment should also have been used to ID need areas

The duty rests with the PC to ensure "suitable" welfare provision is established and maintained. Ball in PC court then. If you consider existing provision suitable for numbers, hygiene purposes etc, then you can stick to your guns. I take it there are no specialist requirement issues (Asbestos removal or other nasty requiring segregated facility?) Should the other contractor choose to provide additional, he'll first of all need your approval to bring that onto Site - entirely at his expense. Key word "suitable".