These are areas that need to be accessed by personnel maintaining roof-top building services installations.

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Note added at 4 hrs (2017-02-01 11:43:16 GMT)
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This gives a general idea of the sort of provision, even if it refers more specifically to "walkways", rather than to "circulation areas" in general:

www.bauder.co.uk/assets/b/a/bauderflatroofdesignconsiderati...
"Whenever there is a requirement for regular foot traffic across a roof, for example to provide maintenance to rooftop plant or a fire escape route, it will be necessary to provide protection to the surface of the waterproofing. It is normally sufficient to provide an extra layer of capping sheet in a contrasting colour to denote the walkway and provide sufficient protection. In cases of extreme traffic, promenade tiles can be bonded to the surface of the capping sheet using hot bitumen or a suitable cold applied adhesive."

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Note added at 9 hrs (2017-02-01 16:41:10 GMT)
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https://en.wikipedia.org/wiki/Circulation_(architecture)In the field of architecture, circulation refers to the way people move through and interact with a building. In public buildings, circulation is of high importance; ...

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Note added at 9 hrs (2017-02-01 16:51:42 GMT)
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https://www.bookdepository.com/Designing-Circulation-Areas-C...
Designing circulation areas: Staged paths and innovative floorplan concepts
edited by Christian Schittich

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Note added at 1 day9 hrs (2017-02-02 17:26:07 GMT)
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Further to Phil's comments re using "access" rather than "circulation". I don't think that it is a major isssue, but access is generally used for routes, e.g. walkways, while circulation areas include those, but also include areas such as space to the side of building services installations for handling equipment etc. If I knew that the areas concerned were all made up of walkways, I'd be perfectly happy to call them "access areas".

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Note added at 1 day9 hrs (2017-02-02 17:29:31 GMT)
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Note that this would matter if the areas concerned were included in a valuation for tax purposes (which would include "circulation areas"), but these rooftop service areas shouldn't be.