Understanding Drying

Do I need a dehumidifier?

Dehumidifiers reduce humidity in enclosed structural environments by removing water vapour from the air.  With proper use, dehumidifiers can be used to dry carpets, floors, walls, building contents and more.  Dehumidifiers can also help prevent secondary damage caused by high humidity.  They are therefore ideal for water damage restoration work, when wet buildings and their contents need to be rapidly dried.   In addition they can reduce the damage caused by condensation or and other pervasive damp issues.


The optimum drying program will be discussed with your technician. There is a range of drying techniques available for drying water and moisture damage. The format chosen will depend on a number of factors:

• Extent of moisture saturation;
• Materials used in construction;
• Construction method and access to damp areas;
• Whether the property is vacated or in use;
• Noise levels tolerable;
• Energy consumption reasonable etc.

Some of the drying techniques are explained here:

1. Room Dehumidification

The dehumidifier is placed in the affected room and blows dry air into the whole space so that all surfaces in the room are dried.

This is a good primary action before installing a more in depth drying method when drying in areas where sensitive materials or objects are located that could be damaged by low RH. Caution needs to be taken to avoid unwanted shrinkage in the room.

2. Dehumidification of Buildings

This is of great use in new building where damp needs to be dried during construction. Materials in a building contain a large amount of building moisture, some of which is in the material after manufacture.

When stored at the work site more moisture can be added. Large amounts of building moisture should be dried before construction is finished.

3. Plastic Enclosure

Where accelerated drying is required to specific areas such as part of a wall or floor, the dehumidifier blows dry air into the plastic ‘tent’ and thereby dries the damage quicker.

Large areas can also be dried within a plastic enclosure where damage to the rest of a space needs to be avoided – ie the low RH is kept within the tented area.

4. Floor Joist Drying

Dry air can be directed from the dehumidifier into the construction, so spaces within floor joists can be addressed.

If greater airflow is required, a low pressure fan can be used. The fan partly sucks room air and partly dry air to therefore dry insulation in floors and walls.

5. Pressure Drying

Floating floor constructions can be dried where water is trapped underneath the slab. This is often faster than dehumidifying the room and waiting for moisture to evaporate up through the floor.

Air is pushed through a turbine into the construction via a system of hoses connected to predrilled holes.

6. Suction Drying

Again for floating floor constructions. The suction is based on dehumidifying the room air. The dry air in the room is sucked down into the building construction using a turbine, which then sucks the moist air from the insulation via a hose system connected to predrilled holes in the construction.

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There stages of the drying process are outlined below. Buildings need to be fully dried before restorative building works can take place. The speed of the drying process depends on the degree and spread of moisture saturation, on what building materials are affected, and also the ambient environmental conditions.

1. Water pump out.

It may be necessary to pump out any excess water. Dehumidifier-Rental can provide puddle pumps to undertake this.

2. Damp assessment

Once water pump-out has been completed, or even straight away if water pump-out is not required, the extent of water saturation can be ascertained. This is undertaken with moisture measuring devices, including thermographic cameras.

This assessment will inform whether any preparatory works are required before the drying program can be set up. This may include invasive works such as cutting access holes in plasterboard walls/ceilings, removing saturated insulation, grinding compounds off concrete floors etc. Any such works will need to be discussed with the client/insurer before commencing.

3. Cleaning and Stripping Out

Firstly the silt and debis left by flood is removed, together with checking gas and electricity supplies and appliances. Stripping out will occur where necessary – likely to include removing damaged and wet furnishings and fittings and hacking off damaged plaster and woodwork, in order to facilitate proper drying out.

4. Disinfecting and Drying Your Property

Disinfecting may be required in advance of drying. This can be assessed with bacterial analysis and mitigated with spray-disinfectant applications.

Drying buildings can take some time as floodwater can penetrate deep into the fabric of properties even if the flooding seems minimal and shallow.

This deep-seated moisture can take a long time to move out through walls and floors, even if the surface appears dry. Full dryness is required so that repair work will be sustainable and damage doesn’t reappear in future.
Drying machines need to be left on for the duration of the period, as any downtime will extend the drying out period. Additional electricity costs incurred should be covered by your insurance. Time required for drying your property can range from weeks to many months.

During the initial drying phase, in saturated spaces, a significant volume of water needs to be removed quickly. This is typically best undertaken with refrigerant type dehumidifiers which maintain in the region of 50% relative humidity and can expel moisture that readily evaporates/migrates out of building materials.

Deep, structural drying often requires the use of dessicant dehumidifiers to draw moisture out of less porous materials. These dehumidifiers create a very low humidity environment which forces moisture to migrate out of dense building materials.

Heating is also recommended during structural drying. This is because warmer air excites moisture particles within building materials, prompting them to evaporate. Also warmer air can hold more moisture, so heating rooms improves the ability of the air to carry moisture out of materials.

Fans circulating air also encourage removal of moisture from building materials, by delivering dry air to the affected areas and driving saturated air to the dehumidifiers.

The drying set-up can be adjusted as required, by our technicians, and monitoring of moisture levels will be documented during the drying phase.

5. Repair and Reconstruction Work

A building contractor is likely to be appointed to undertake the repair and reconstruction work. Your insurer is responsible for the work of builders they appoint. If you prefer, you may be able to use your own builder.

Your insurer can also discuss with you whether you want the repair works to include those which improve resistance and resilience to future flooding. If this doesn’t cost more than the cost of repairing your home to its pre-flood condition then your insurer will not charge for these changes.

Most contents policies will pay for the full cost of replacing damaged items with the equivalent new ones. If the value of your contents is more than the sum insured the settlement of your claim may be reduced to reflect this.

Note: Be Aware of Health Risks:

The degree to which caution about health effects need to be taken depends largely on the type of water contamination and the passage of time from time of flood.

Flood water can be either ‘white’, ‘grey’ or ‘black’ water.

While white water is uncontaminated at the time of flood. Grey water is wastewater generated from domestic activities such as laundry, showers, dishwashing etc. Black water contains human waste.

Flood water therefore is often contaminated and, even if it appears ‘clean’, may include elements that can cause a range of illness. Personal hygiene, including washing hands and covering cuts or scratches, is very important. Always wash hands before preparing food, eating, drinking or smoking.

Within a few days mould can form, due to the damp environment and this can affect the throat, nasal passages and lungs.

Young children, the elderly and those with immune system deficiency should be kept away from properties that have been flooded until they have been passed safe for habitation. Medical advice should be sought immediately if any health concerns are identified.


If you need our dehumidifier hire services, damp assessment expertise, emergency flood response, or simply advice on how to dry your building, please call us on 0800 078 6999 or email info@dehumidifier-4-hire.co.uk