It seems incredible, but researchers from the University of Hull verified it in a laboratory.
The team wanted to know if a cheap and easily available solution could reduce water entering through the doors of a house. Instead of waiting for a real flood, they prepared controlled trials that allowed them to compare different protections under similar conditions and carefully measure their results.
The advantage of the laboratory is that it allows making a comparison that is difficult to repeat on the street. Two homes can have similar doors and still be exposed to different water levels. If one receives less water than the other, it would be difficult to know how much is due to the protection installed and how much is due to the differences between the two situations.
They simulated floods up to sixty centimeters deep and tested different ways of protecting home doors. By placing duct tape on the outside, sealing its cracks, leaks decreased between 97 and 98 percent. More than with the tested sandbags! The secret? The tape covers the small gaps through which water seeps.
The percentage describes the reduction in leaks during the test. To get an idea of what it represents, let’s imagine that, in two tests of equal duration, one hundred liters enter through the unprotected door. A reduction of 97 to 98 percent would be equivalent to between two and three liters passing through in the second trial. It is an example to interpret the figure.
Even if a door appears to close perfectly, it often leaves small openings around the frame, at the joints, and near the threshold. When the external level rises, the pressure of the water favors it to cross these separations. A well-placed adhesive barrier can make this step more difficult and considerably reduce leaks.
A slit may be so narrow that it is barely visible to the naked eye. Its effect is better understood if we think about the time during which the water remains against the door. Even a reduced pitch can allow an appreciable amount to accumulate on the other side if the level remains high.
The comparison is striking because sandbags are a common image of flood emergencies. However, they do not always form a tight seal: water can find paths between them. That does not make any tape equivalent protection or guarantee that it will work on all doors. Surface, placement and flood conditions matter.
A warped joint or a slightly uneven frame can change both the size of the gaps and the ease with which the adhesive sets.
But be careful, it does not stop a flood or prevent water from entering walls, floors or drains. It can only be a temporary aid, placed before the water arrives and always without putting oneself in danger.
When faced with an alert, the priority is to follow the instructions of the authorities, avoid flood-prone areas and leave the place when ordered. No laboratory result justifies staying to protect a home.
REFERENCES
Stuart J. McLelland, Andrew Manson, Brendan J. Murphy, Giles Davidson, Robert Thomas, Joseph Shaw and David Furnues (2026). “Testing the Performance of Low-cost, Temporary Property Flood Resilience (PFR) Solutions.” From the University of Hull, to Flood Re. Zenodo, 15 October 2026
