Probably not as such areas are generally well ventilated, but worth a look at the definitions of confined space and specified risk in L101

I'd be more concerned with underfloor ducts, undercrofts and crawl spaces, to be honest. Not forgetting asbestos containing materials, the legacy of poor stripping techniques and the real risk of disturbing friable material when pulling through replacement cables. Contract contingencies should anticipate involvement of asbestos specialists, refurbishment survey, camera work, contract delays and associated enabling or remedial works. Lofts, other than a potential for heat distress, are unlikely (by themselves) to give rise to any of the specified risks to qualify as a confined space as defined. Work at height, poor lighting and falling through fragile ceilings are the no-brainers for loft work, along with the significant discomfort of working with or near rock wool insulation.