> For the complete documentation index, see [llms.txt](https://docs.os.uk/osngd/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.os.uk/osngd/using-os-ngd-data/os-ngd-buildings/known-limitations.md).

# Known limitations

There are some agreed and known challenges with capturing and publishing data for Building Age, Construction Material, Basement Presence, Number of Floors, Roof Attribution, Building Height and Physical State:

* There is no single, definitive measurement or information available for any of these attributes at a national scale.
* There are limited and sometimes conflicting sources of information from which to derive values.
* The real world can be very difficult to represent in data. For example, new builds can be made to look like older buildings.
* The level of estimated conformance is perfect for 1 to 2 floors 95% of the time, but it reduces with the increasing number of stories. 95% of all buildings that have 5 or more floors will have the correct number of floors value (within 1 floor) recorded when compared with the real world.
* It is difficult to accurately predict floor numbers for complex buildings with towers, spires, roof furniture, overhanging vegetation, etc.
* All buildings less than 4m² won’t be allocated with roof attribution information
* Roofs covered by >80% solar panels or roof furniture will get a value of Unknown.
* Change suppression on Building Part (if Building Part geometry has not changed and the height value is within ± 1.5m of the previous value, the previous value will be retained).
* **Physical State attribute:**
  * Ordnance Survey predominantly captures Building features that are 'Under Construction' where they are associated with completed features that are being captured – for example, a developing housing estate or industrial park. For a smaller development, without significant phases, it's likely that buildings will be complete when the capture is undertaken and therefore the features for these buildings will not pass through a transition from 'Under Construction' to 'Built'.
  * For buildings that have become 'Derelict' or lie within a Site considered to be 'Derelict', we have fewer reliable sources of change intelligence and, as such, OS does not expect to have complete coverage of all buildings that are ‘Derelict’.   


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