That's the way it is where I live anyway, houses are 3 bed semis with a high pitch A roof to the side so are very suitable for attic conversions. Many now have these conversions. When selling they are always described as a 3 bed semi with attic conversion.
Even though the attic is usually the biggest room in the house, wired, plumbed, insulated, heated and has its own en-suite, in most cases it can never be called anything other than a non habitable attic conversion, but prospective buyers will always see it for what it is.
Those with a good quality conversion always get a premium price and I have never heard of any planning issues or problems with banks or insurers from the many that have sold around here over the years.
I have an Architects cert saying my conversion complies with all regulations etc for a non habitable attic conversion. When doing the inspection the architect examined the eaves to ensure the roof timbers that had to be removed to facilitate the conversion were properly replaced so the roof was not compromised in any way.