"Cleanroom" doesn't have a universally agreed meaning. If you already are achieving consistently controlled and sufficiently low bioburden levels (i.e. not exceeding some upper threshold, every time), you already have an environmentally controlled area.
The "controls" for instance might be secondary to other purposes, i.e. your whole factory is maintained at that level of cleanliness for other reasons. That's fine...there's no requirement that controlled bioburden be achieved via capabilities put in place specifically for that purpose. All that matters is the result, and perfect consistency.
If your present bioburden level and character is consistent with the capability of your sterilization process and the other requirements of your product (i.e. implantables and fluid contact devices have pyrogenicity requirements, etc.), you're already where you need to be. If not, you may have to step up your game to achieve more cleanliness. If the only way to assuredly get and perfectly consistently maintain the level of cleanliness you need is to create a purpose built space, so be it.
Bottom line: it's results that matter. There is no requirement to have a cleanroom unless you need one to achieve the required results, which are a requirement.