Flood Risk Assessment for Barn Conversion

Rural sites in England frequently have flood risk from sources that do not appear on the standard EA Flood Map for Planning. Ordinary watercourses, including field drains, ditches, becks and streams that are not designated as main rivers, can flood during intense rainfall events and affect sites that appear to be in Flood Zone 1. Surface water overland flow from surrounding agricultural land can pond against buildings at low points in the landscape. Groundwater flooding can affect sites on chalk, limestone or gravel geology during prolonged wet periods. None of these sources is reliably mapped at a scale relevant to an individual barn or farmyard. A site-specific assessment is the only reliable way to establish whether they present a planning constraint.

Prior Approval applications for barn conversions under Class Q Permitted Development rights are not exempt from flood risk consideration. The Environment Agency provides standing advice on Prior Approval applications in flood risk areas, and planning authorities are required to consider flood risk as part of the Prior Approval determination. An application that does not address the EA standing advice where it applies, or that does not demonstrate that the change of use to residential is appropriate in flood risk terms, can be refused under Prior Approval as well as full planning permission.

Where a barn conversion site is in Flood Zone 2 or 3, the question of whether the Sequential Test applies depends on the application route. A full planning application for a new dwelling in Flood Zone 2 or 3 triggers the Sequential Test. A Class Q Prior Approval application is a change of use and is exempt from the Sequential Test and Exception Test under the NPPF. However, the FRA must still demonstrate that the proposed residential use is safe and appropriate in flood risk terms for the lifetime of the development. Where the site is in Flood Zone 3b functional floodplain, a change of use to residential is not permitted regardless of application route. The FRA in Zone 3b must demonstrate that the use is water-compatible, which residential use is not.

• Any barn conversion in Flood Zone 2 or 3, regardless of size or application route.
• Barn conversions in Flood Zone 1 where ordinary watercourse, surface water or groundwater flooding is documented or suspected.
• Prior Approval applications under Class Q where the EA has issued standing advice or the site is identified in the SFRA as being at flood risk.
• Barn conversions on sites of 1 hectare or more in Flood Zone 1.
• Conversions in locations where the local planning authority or LLFA has indicated flood risk is a material consideration.
• Any conversion where the change from agricultural to residential increases flood vulnerability and any flood risk from any source is present.

We prepare flood risk assessments for barn conversion applications across England and Wales, under both full planning permission and Prior Approval routes. We are familiar with the Class Q Permitted Development framework and the specific flood risk requirements that apply to Prior Approval determinations.

We assess all relevant flood sources for rural sites, including ordinary watercourse flooding, surface water overland flow from surrounding agricultural land and groundwater flooding, not just the standard flood zone designation. These are the sources most likely to affect a rural barn conversion site and most likely to be missed by a standard flood risk screening.

We are familiar with the vulnerability classification framework and the Sequential Test and Exception Test requirements that apply to barn conversions in higher flood zones. We scope assessments to be proportionate to the specific site and application type.