How High Above the Floodline Must a Floor Be? Freeboard Rules in South Africa

Freeboard is the vertical margin between the design flood level and a floor. Only a few South African municipalities set a figure. Cape Town requires floors above the 1:100-year flood level for most development its floodplain policy allows, and its roads and stormwater standards specify at least 250 mm for new urban developments, measured to the energy level. Msunduzi requires ground floors at least 300 mm above the highest flood recorded on the land. Most of the municipalities we checked set no number, which leaves the margin to the floodline report.

Setting floor or platform levels near a river? We give you the design flood level at each building and recommend a freeboard with the reasons for it.

Floodline determination

What freeboard is for

A floodline is a modelled estimate. Freeboard covers what the model cannot represent exactly:

• Uncertainty in the flood estimate and in the roughness and terrain the model uses.
• Waves and surges: wind on a wide floodplain, and the wash from vehicles on a flooded road.
• Debris and blockage: a culvert that blocks in a flood raises the level upstream.
• Change after the line is drawn: development upstream, sediment, and heavier rain. Our posts on why floodlines go out of date and climate change and floodlines cover these.

A floor exactly at the 1:100-year level has no margin for any of them.

What municipalities require

Municipality	Floor level rule	Source
Cape Town	For most development the policy allows in the floodplain, floors above the 1:100-year flood level; basements for non-habitable use flood-proofed to the 1:50-year level. The roads and stormwater standards, for new urban developments: “Floor levels are to be 250mm (minimum) above the 1:100 flood levels. (Calculated considering the theoretical energy levels)“	Floodplain and River Corridor Management Policy 2009; Standards and Guidelines for Roads and Stormwater v3.0 (2022), s10.3.3
Msunduzi (Pietermaritzburg)	Concrete ground floors at least 300 mm above “the maximum known level reached by floodwaters on the land… as ascertained from records kept by the Municipality”; no habitable buildings within the 1:50-year floodline	Single Land Use Scheme 2024, cl 5.43
George	Lowest floor above the 100-year flood level “where possible”	Stormwater By-law 2023, s26(4)(d)
Others we checked	No figure published; set case by case	Conditions of approval

The only national freeboard figure we found is for mine dirty water dams: 0.8 m above full supply level (GN 704, regulation 6). That is a spill margin for dams, not a floor-level rule.

Note that Msunduzi’s reference is the historical record, not the 1:100-year floodline: where no level is on record, the Municipality approves a minimum height. Cape Town’s policy also covers existing rights: on building plans for properties already zoned, floors should be above the 100-year level where practically possible, and no buildings are allowed in the high hazard zone.

Energy level or water surface?

Cape Town measures from the energy level, not the water surface. The energy level adds the velocity head (the height equivalent of the water’s speed) to the water level. Where water flows fast, the difference can be large; where it ponds, there is almost none. A floor set 250 mm above the water surface in a fast-flowing reach may be below the energy level, so check which one the municipality means before setting levels.

Choosing a freeboard where none is set

Where the municipality sets no figure, the floodline report should recommend one and say why. The things that push it up:

• Fast or deep flow at the building, and a high hazard if the floor floods.
• Culverts or bridges just downstream that could block and back water up.
• Uncertain data: coarse terrain, no survey of the channel, or a short flow record.
• Vulnerable uses: homes, schools, clinics, and anywhere people sleep.
• A wide, open floodplain where wind waves can build up.

Freeboard on the floor is not the only measure. The access route, the electrical installation and anything stored at ground level need thinking about too. Our post on building inside a floodline covers the other measures, and bridge waterway assessments covers freeboard to the underside of a bridge.

See our floodline determination service, or send us the site layout and we will give you the design flood level at each building.

This post explains the documents listed below. Requirements change and are applied case by case, so confirm them with the relevant authority before relying on them.