Ordnance Datum
The term ‘Ordnance Datum’ refers to the height of mean sea-level, taken from a reference point at Newlyn in Cornwall. This is basis of the national height system for Britain.
The Newlyn Ordnance Datum was preceded by a Liverpool levelling, started in 1840 using a bench mark on St John's Church. In 1844 the datum was changed to the tidal pole in Victoria Dock, but from 1921, this has been generally superseded by the Newlyn Ordnance Datum.
In some remote islands such as Shetland and the Hebrides, datums are based on a local determination of mean sea level.
Ref https://www.ordnancesurvey.co.uk/gps/legacy-control-information/liverpool-to-newlyn
The term Above Ordnance Datum (AOD) refers to a height above the Ordnance Datum. Measurements are given a + or a – sign to signify which side of Ordnance Datum it falls.
[edit] Related articles on Designing Buildings
Featured articles and news
Costs and insolvencies mount for SMEs, despite growth
Construction sector under insolvency and wage bill pressure in part linked to National Insurance, says report.
The place for vitrified clay pipes in modern infrastructure
Why vitrified clay pipes are reclaiming their role in built projects.
Research by construction PR consultancy LMC published.
Roles and responsibilities of domestic clients
ACA Safety in Construction guide for domestic clients.
Fire door compliance in UK commercial buildings
Architect and manufacturer gives their low down.
Plumbing and heating for sustainability in new properties
Technical Engineer runs through changes in regulations, innovations in materials, and product systems.
Awareness of the Carbon Border Adjustment Mechanism
What CBAM is and what to do about it.
The new towns and strategic environmental assessments
12 locations of the New Towns Taskforce reduced to 7 within the new towns draft programme and open consultation.
Buildings that changed the future of architecture. Book review.
The Sustainability Pathfinder© Handbook
Built environment agency launches free Pathfinder© tool to help businesses progress sustainability strategies.
Government outcome to the late payment consultation, ECA reacts.
IHBC 2025 Gus Astley Student Award winners
Work on the role of hewing in UK historic conservation a win for Jack Parker of Oxford Brookes University.
Future Homes Building Standards and plug-in solar
Parts F and L amendments, the availability of solar panels and industry responses.
How later living housing can help solve the housing crisis
Unlocking homes, unlocking lives.
Preparing safety case reports for HRBs under the BSA
A new practical guide to preparing structural inputs for safety cases and safety case reports published by IStructE.
Male construction workers and prostate cancer
CIOB and Prostate Cancer UK encourage awareness of prostate cancer risks, and what to do about it.