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.

TradeCalculator

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.