How long does it take to dry a flooded house?

Drying time depends primarily on wall construction: timber frame walls dry in about 4 weeks, cavity brick in 8 weeks, solid 225mm brick in 12 weeks, and thick stone walls can take 6 months or more. Concrete floors typically take 4-8 weeks. Professional dehumidification speeds up the process significantly.

What size dehumidifier do I need?

As a rule of thumb, allow 10 litres/day extraction capacity per 30m³ of room volume. A typical room (4×5×2.4m = 48m³) needs a 20L/day commercial dehumidifier. For severe flooding, multiple units may be needed. Domestic dehumidifiers (5-10L/day) are too small for flood drying.

Should I use heaters to speed up drying?

Yes, maintaining a temperature of 18-22°C significantly improves drying rate. Warm air holds more moisture, which the dehumidifier can then extract. However, do not exceed 30°C as this can cause salts to crystallise and damage plaster. A combination of heat + dehumidification + air movement is most effective.

When can I replaster after flooding?

Do not replaster until moisture meter readings show the walls are within acceptable limits (below 5% WME for plaster, below 3% for brick). Replastering too early traps moisture in the wall, leading to ongoing damp problems. Use a renovation plaster (salt-resistant) after flood damage.

Do I need fans as well as dehumidifiers?

Yes. Air movement fans are essential to distribute air across wet surfaces, accelerating evaporation. Without air movement, a stagnant boundary layer of humid air forms against the wet surface, slowing evaporation. Place fans to direct air across wet walls and floors, not directly at the dehumidifier.

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Flood Drying Calculator — Dehumidifier Size & Drying Time

Estimate drying time and dehumidifier requirements after flooding, based on wall construction, flood depth and room volume.

Room Length

Room Width

Wall Construction~12 weeks typical drying

Flood Depth

Depth of flood water above floor

Equipment Cost Per Day (optional)

Dehumidifier + fan hire cost

How We Calculate This

This calculator estimates drying equipment and timescales based on room dimensions, wall type and flood depth.

The formula

Dehumidifier Size = ceil(Room Volume / 30) × 10 L/day

Fans = ceil(Perimeter / 5)

Typical drying times

Timber frame: 4 weeks
Cavity brick: 8 weeks
Solid brick 225mm: 12 weeks
Solid brick 340mm: 18 weeks
Stone 450mm: 26 weeks

Frequently Asked Questions

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Last updated: March 2026

All calculations are estimates. Verify with your supplier.