Flood zone
A flood zone is an area that can be flooded by a flood with a defined probability, stated as a return period. For new homes, the 200-year flood normally applies (a 1/200 probability in any given year), while buildings that are critical to society, such as hospitals and fire stations, must be protected against the 1,000-year flood. Flood zones are included in municipal land use plans as a hensynssone (consideration zone) under the Planning and Building Act, and the requirements for safety levels are set out in TEK17 section 7-2.
Safety classes F1, F2 and F3 in TEK17 section 7-2 grade both the type of work that is permitted and the flood level it must withstand. F1 covers garages, boathouses and outbuildings with low damage potential and requires protection against the 20-year flood. F2 covers homes, offices and commercial buildings and requires protection against the 200-year flood. F3 covers hospitals, care homes, emergency response and infrastructure facilities and requires protection against the 1,000-year flood. Protection can be achieved by raising the floor, building a flood embankment, changing the use of the ground floor, or placing the work outside the zone. Floor layouts where only storage and technical rooms sit below the flood level and the living floor itself sits above it are a common practical adaptation.
The underlying data comes from NVE (the Norwegian Water Resources and Energy Directorate), which calculates and maps flood zones along priority watercourses, and from the municipalities' own flood mapping. NVE's flood awareness maps cover larger areas at coarser resolution and are used as a first-line warning; flood zone maps with located return periods are finer products, often based on hydraulic modelling. Both are available as open map layers from NVE Atlas and can be shown together with the matrikkel in municipal plans.
Flooding covers watercourse flooding (rivers and lakes bursting their banks), urban flooding (surface water that the network cannot handle), coastal flooding (storm surge and wave run-up) and ice-jam flooding. NVE's flood zone maps mainly cover watercourse flooding; for coastal flooding, Kartverket produces sea level maps that assess storm surge and future sea level rise. Climate allowances in municipal plans are typically 20% to 40% higher flood discharge towards the year 2100, depending on the catchment; the figures are updated regionally and must be taken from the current climate profile.
The consequences for a developer are concrete. Work inside a flood zone without documented protection to the correct safety class will be rejected, and the building application must be accompanied by a flood assessment from a qualified expert (a geotechnical engineer or hydrologist). Existing buildings inside a flood zone are not automatically required to carry out work, but insurers price flood exposure into the premium or deductible, and in the worst case can refuse to insure new buildings that fall below the safety class. The natural damage scheme through Norsk Naturskadepool covers damage, but not repeated events in the same building without remedial work.
The difference from a landslide hazard zone is the type of hazard: a flood zone concerns water from watercourses or the sea, while a landslide hazard zone concerns mass movement on sloping terrain. An area can fall within both, particularly in steep side valleys. A flood zone can also overlap the building line along a watercourse under section 1-8 of the Planning and Building Act; the two instruments have a different legal basis and a different zone, but both regulate where and how you can build near water.
In Placepoint, flood zones and NVE's awareness maps are shown as map layers, and you will find a walkthrough of the climate risk flow in the example Climate risk and ground conditions.
From Placepoint's dictionary: Flood zone
More information: NVE: floods and landslides, DiBK: TEK17 section 7-2, NVE Atlas: map data
English: Flood zone (NVE-mapped area exposed to river or coastal flooding).
Frequently asked questions
What does the 200-year flood mean?
A flood with a 1/200 probability of occurring in a given year, that is, a severe event that over time is expected to happen once every 200 years on average. For homes, this is the reference level for protection under TEK17 section 7-2.
What is the difference between a flood zone and a flood awareness map?
Flood zone maps are detailed model calculations with located return periods. Awareness maps are coarser overviews that show areas where flood hazard must be assessed, but without a specific level.
Which safety classes apply to flooding?
F1 (20-year flood, low damage potential), F2 (200-year flood, homes and offices), F3 (1,000-year flood, buildings critical to society). The class determines the level of protection the work must meet.
Can I build in a flood zone?
Yes, but the building application must document that the work is protected to the relevant safety class, or that it is placed outside the zone. Protection can be raising the building, a flood embankment or another technical solution.
Does insurance cover flood damage?
The natural damage scheme through Norsk Naturskadepool normally covers flood damage, but the insurer can require a deductible and can refuse to renew cover after repeated damage without remedial work.