TAN 15 Explained: Flood Risk and Development in Wales

The current version came into force on 31 March 2025, replacing the 2004 edition. It introduced a revised framework centred on the Flood Map for Planning and the updated Flood Risk Areas Direction.

TAN 15 supports Planning Policy Wales and operates within the national framework established by Future Wales. Although it is guidance rather than primary legislation, it is a material consideration in both development plan preparation and planning application decisions.

In practice, TAN 15 determines how flood zones are defined, which types of development are appropriate in each zone, when a Flood Consequences Assessment is required, what constitutes acceptable flood consequences, and how climate change and coastal erosion must be considered over the lifetime of development.

The Flood Map for Planning

Flood risk under TAN 15 is assessed using the Flood Map for Planning, produced by Natural Resources Wales.

This map is distinct from the general Wales Flood Map. It is specifically prepared for planning purposes and incorporates central climate change projections into mapped flood extents.

It identifies flood risk from rivers, the sea and surface water, and defines Zones 1, 2 and 3 as well as Defended Zones.

Planning decisions must rely on the most up-to-date version of the Flood Map for Planning at the time of determination.

Flood Zones Under TAN 15 Wales

TAN 15 divides land into three principal flood zones.

Defended Zones identify areas protected by formal flood defences meeting defined minimum standards. However, the presence of a defence does not remove flood risk entirely. Residual risks, including overtopping and breach scenarios, must still be assessed.

Development Vulnerability

TAN 15 categorises development according to vulnerability.

Highly vulnerable development includes all residential dwellings, as well as uses such as schools and hospitals. Residential development is therefore explicitly treated as highly vulnerable.

Less vulnerable development includes most commercial and industrial uses.

Water compatible development includes uses that require a waterside location or can tolerate periodic flooding.

Vulnerability classification is central to determining whether development may be acceptable in Zone 2 or Zone 3.

Flood Consequences Assessment (FCA)

In Wales, applicants must prepare a Flood Consequences Assessment where required under TAN 15.

An FCA is generally required for development in Zone 2 or Zone 3, and for development in areas at risk from surface water. It may also be required where development outside mapped zones could affect flood risk elsewhere.

The purpose of an FCA is to demonstrate that flood consequences are acceptable.

This includes assessing flood sources and mechanisms, modelling flood depths and velocities, considering climate change scenarios including upper-end allowances, demonstrating safe access and egress, and ensuring no increase in flood risk elsewhere.

For highly vulnerable development, buildings should be flood free in the 1 per cent annual probability fluvial event plus climate change and the 0.5 per cent tidal event plus climate change.

In the 0.1 per cent annual probability event plus climate change, flood conditions must not exceed defined tolerable thresholds. For highly vulnerable development, this includes a maximum depth of 600 mm and a maximum velocity of 0.15 m/s.

Resilience measures alone cannot justify development where tolerable thresholds are exceeded.

Flood Zone 3 and Residential Development

Flood Zone 3 Wales is subject to the strongest policy constraints under TAN 15.

The 2025 version states that new highly vulnerable development on greenfield land in Zone 3 should not be permitted. As residential development is classified as highly vulnerable, this significantly restricts new housing proposals in high-risk areas.

The Town and Country Planning (Flood Risk Areas) (Wales) Direction 2025 also requires local planning authorities to notify Welsh Ministers where they are minded to approve certain highly vulnerable development in Rivers and Sea Zone 3 on previously undeveloped land.

For residential development, this notification requirement can apply to a single new dwelling resulting in a net increase, subject to specified exemptions such as replacement dwellings and certain conversions.

The Direction applies to rivers and sea flood risk, not surface water alone.

Climate Change and Coastal Erosion

Climate change is embedded throughout the 2025 version of TAN 15.

The Flood Map for Planning incorporates central climate change projections. However, site-specific FCAs must also consider upper-end climate change allowances in accordance with Welsh Government guidance.

Development must remain safe for its design lifetime.

TAN 15 also addresses coastal erosion risk and states that development should not be permitted where it would be at risk from coastal erosion over its lifetime.

Sustainable Drainage

In Wales, sustainable drainage systems operate under a separate statutory regime via SuDS Approval Bodies.

TAN 15 requires sufficient drainage information at planning stage to demonstrate that flood risk will not increase elsewhere.

Planning permission does not remove the need for SuDS approval.

Frequently Asked Questions About TAN 15

What is TAN 15 in Wales?

TAN 15 is Welsh Government planning guidance on development, flooding and coastal erosion. It explains how flood risk must be assessed and managed when preparing development plans and determining planning applications in Wales.

What is Flood Zone 3 in Wales?

Flood Zone 3 identifies land at high probability of flooding from rivers, the sea or surface water. It is the most constrained category under TAN 15, particularly for highly vulnerable development such as housing.

When is a Flood Consequences Assessment required?

A Flood Consequences Assessment is usually required for development in Zone 2 or Zone 3, and for proposals that may affect flood risk elsewhere. It must demonstrate that flood consequences meet the acceptability criteria set out in TAN 15.

Can you build a house in Flood Zone 3 in Wales?

Residential development is classified as highly vulnerable under TAN 15. New highly vulnerable development on greenfield land in Zone 3 should not be permitted. Certain proposals may also require Ministerial notification under the 2025 Direction.

What is a Defended Zone under TAN 15?

A Defended Zone identifies land protected by formal flood defences meeting defined standards. However, residual risk must still be assessed, including breach and overtopping scenarios.

Does TAN 15 include climate change?

Yes. Climate change projections are embedded in the Flood Map for Planning and must also be assessed in detail within Flood Consequences Assessments.

Flood Risk Advice Under TAN 15 Wales

Applying TAN 15 requires careful interpretation of policy alongside detailed technical modelling. The interaction between zoning, vulnerability classification, climate change allowances and defined acceptability tests means compliance depends on both strategy and evidence.