Freeboard
Culvert, screen and outfall manual, (CIRIA C786) published by CIRIA in 2019, defines freeboard as: ‘An allowance for uncertainty in design water level and any other physical processes that may affect the ability of an asset to withstand the design water level such as wave action or superelevation.’
See also Residual uncertainty allowance.
Containment systems for the prevention of pollution, Secondary, tertiary and other measures for industrial and commercial premises (CIRIA C736), published by CIRIA in 2014 defines freeboard as: ‘An allowance in the form of increased height of a containment wall for additional capacity over and above the minimum design requirement.’
Rules of Thumb, Guidelines for building services (5th Edition) BG 9/2011, by Glenn Hawkins, published by BSRIA in 2011, defines freeboard as: ‘The vertical distance in a water tank between the maximum water level and the top of the tank’. This definition is repeated in BG 87/2024, Useful Information Guide, written by Chin Hang “Kay” Lam and published by BSRIA in 2024.
High Speed Rail (Crewe – Manchester) Environmental Statement, Glossary, abbreviations and references, published by the Department for Transport in 2022, defines freeboard allowance as:
The height from the maximum design level of a watercourse to:
- the adjacent banks of an open channel, to provide a factor of safety against flooding; or
- the soffit (underside) of any culvert or bridge above, to reduce the risk of blockage by floating debris, etc.’
[edit] Related articles on Designing Buildings
Featured articles and news
ECA, JIB and JTL back Fabian Society call to invest in skills for a stronger built environment workforce.
Women's Contributions to the Built Environment.
Calls for the delayed Circular Economy Strategy
Over 50 leading businesses, trade associations and professional bodies, including CIAT, and UKGBC sign open letter.
The future workforce: culture change and skill
Under the spotlight at UK Construction Week London.
A landmark moment for postmodern heritage.
A safe energy transition – ECA launches a new Charter
Practical policy actions to speed up low carbon adoption while maintaining installation safety and competency.
Frank Duffy: Researcher and Practitioner
Reflections on achievements and relevance to the wider research and practice communities.
The 2026 Compliance Landscape: Fire doors
Why 'Business as Usual' is a Liability.
Cutting construction carbon footprint by caring for soil
Is construction neglecting one of the planet’s most powerful carbon stores and one of our greatest natural climate allies.
ARCHITECTURE: How's it progressing?
Archiblogger posing questions of a historical and contextual nature.
The roofscape of Hampstead Garden Suburb
Residents, architects and roofers need to understand detailing.
Homes, landlords. tenants and the new housing standards
What will it all mean?
The Architectural Technology podcast: Where it's AT
Catch-up on the latest episodes.
Edmundson Apprentice of the Year award 2026
Entries now open for this Electrical Contractors' Association award.
Traditional blue-grey slate from one of the oldest and largest UK slate quarries down in Cornwall.
There are plenty of sources with the potential to be redeveloped.
Change of use legislation breaths new life into buildings
A run down on Class MA of the General Permitted Development Order.
Solar generation in the historic environment
Success requires understanding each site in detail.