Flood Risk Assessment, Flood Zone 1 Barn Conversion, Hoxne
The conversion of two agricultural barns on Syleham Road, Hoxne, Suffolk, into two dwellings, in Flood Zone 1 but at high risk from surface water in the courtyard between them. The Air & Flood Consultants FRA converts the Environment Agency's banded surface water depths into an estimated flood level of about 38.5 m AOD using LiDAR, sets both floors at 38.50 m AOD with flood-resistant entrances to about 38.80 m AOD, and regrades the courtyard hollow. A 242 m walking route along Syleham Road crosses no mapped danger for some. The FRA was issued on 20 October 2026 for an application to Mid Suffolk District Council that is yet to be registered.
The proposal converts two existing agricultural barns on Syleham Road, Hoxne, near Eye in Suffolk, into two dwellings within their existing footprints. A third barn is retained as an outbuilding, and the existing access and concrete track from Syleham Road are upgraded, with parking, bin storage and landscaping. The site lies in Flood Zone 1, but a change of use to dwellings increases its vulnerability, and the Environment Agency maps surface water on the site, so a site-specific flood risk assessment was needed. Tidal, fluvial, groundwater, sewer and reservoir risks were assessed as low, and surface water risk as high.
The Environment Agency's Risk of Flooding from Surface Water (NaFRA2) places a pocket of about 115 m² of the 1 in 30 (3.3% AEP) extent in the courtyard and parking area between the two dwellings, at depths below 300 mm, where LiDAR ground falls to about 37.7 m AOD. Neither dwelling lies within it. With climate change the 1% AEP extent covers about 637 m² of the site, or 31.9%, including about 49 m² of one dwelling and 55 m² of the other at depths mainly between 150 and 300 mm, and the courtyard in front of both entrances reaches 300 to 600 mm.
The standing advice asks for banded depths to be converted to an estimated flood level. With no topographical survey, each mapped cell within 3 m of a dwelling was given its LiDAR ground level plus the upper limit of its depth band. The result is about 38.5 m AOD at both dwellings, 0.30 to 0.35 m above adjacent ground. Both finished floors are therefore to be set at 38.50 m AOD. All external doors are to be flood resistant to 600 mm above adjacent ground, about 38.80 m AOD, giving at least 300 mm above the estimated level at every entrance. The courtyard is to be regraded so that the hollow no longer collects water against the entrances, with the water it now stores held on site in permeable paving sub-base so that no flow is pushed towards neighbouring buildings or the road. Ground floors are to be solid with resilient finishes to 600 mm, sockets and controls at least 1.0 m above floor level, self-closing air bricks and non-return valves.
No flood warning service covers surface water, so the plan sets Met Office heavy rain warnings and visible ponding in the courtyard as the triggers, and the response is to stay inside until the courtyard drains. The walking route follows the southern side of Syleham Road north-east for 242 m to rising ground. Sampled every 1 m against the NaFRA2 hazard mapping, it crosses no rating of 0.75 or more (danger for some), present day or with climate change. Both road approaches were checked for the emergency services: neither reaches a rating of 2.0 (danger for all), and the north-east approach stays below danger for most in every mapped event.
Air & Flood Consultants issued the final FRA on 20 October 2026. The planning application is yet to be registered, and its reference is to be added when it appears.
More on these services:
Flood risk assessments: https://www.airandfloodconsultants.co.uk/floodrisk
Flood evacuation plans: https://www.airandfloodconsultants.co.uk/flood-evacuation-plan
Finished floor levels in flood zones: https://www.airandfloodconsultants.co.uk/post/finished-floor-levels-flood-zone