Redbourn has a small flood risk from the River Ver and a larger one from heavy rain. Very few postcodes are in the river flood zones. About one in ten carries a high risk on at least one measure. No flooding is on record. Most of the danger here comes from rain that has nowhere to drain, not from the river.
The Environment Agency's river-and-sea flood zones cover very little of Redbourn. About 2% of the village's postcodes are in zone 2, the medium-probability fringe, and about 1% are in zone 3, the highest-probability band. The two are separate bands, with zone 2 lying beyond zone 3, so the shares are not added together. The Ver once supported a watercress business on its water meadows, and watercress only grows in ground that stays wet, which is why the river ought to be the first thing a buyer looks for on a map.
The river map leaves out rain that falls faster than the ground and drains can take it. In Redbourn that kind of flooding accounts for more of the risk than the river does, and it is folded into the postcode shares further down this page.
If the Environment Agency's climate change allowance is added to its river model, about 6% of Redbourn's postcodes fall within a flood zone. That is the agency's view of how the zones could widen, and it is worth knowing when buying a home you plan to keep for decades.
For insurance, most of Redbourn should be routine. A house in or near the zones, or one in a dip where surface water collects, may get a higher premium, a higher excess or more questions from the insurer. An insurance quote for the exact address, obtained while the sale is still at the solicitor stage, will show which kind of house it is.
On a broader measure that counts a postcode if it reaches a given level on any one of several flood indicators, surface water among them, about 9% of Redbourn's postcodes rate high, about 12% medium and about 29% low. One postcode can appear in more than one of those indicators, so the measure is wide by design.
The Environment Agency's rivers-and-sea mapping lists only seven of Redbourn's postcodes as carrying any risk at all, and they contain 79 properties. Of those, four are at high risk, two at medium, 11 at low and six at very low. Three of the four high-risk properties are homes. That is a small number, and a buyer can find out whether a particular house is one of them in a few minutes.
About 1% of postcodes are in the high-risk river extent without any defence in the model, and about 1% are in it with a defence present. "Defended" only means the model includes a structure such as a wall or bank, not that the house stays dry. A sales particular that uses the word to settle the question has said nothing about how well the defence performs.
The nearest tide gauge is at Portsmouth, where sea level rose by about 2 millimetres a year between 1962 and 2023. Redbourn is a long way inland and sits beside a chalk stream, so that figure has nothing to do with this village's flood risk.
None of Redbourn's postcodes appears on the historic flood record. That is reassuring, but it only means no flooding has been recorded, so a home in one of the few risk postcodes still needs checking properly.
Redbourn's flood risk is middling. The river affects only a few homes, and the bigger risk is surface water, which varies from street to street.