How to reduce humidity in the home

Excess humidity in the home can be a real issue. Often appearing in the form of small droplets of water on walls and windows, an elevated humidity rate can lead to the development of mould on surfaces (walls, floors and furniture) and can create health problems. Homes that are properly insulated should not have any major humidity issues; those that are poorly insulated will be the worst affected.

Poor thermal insulation

If the attic or roof is poorly insulated, or the insulation in place has lost its thermal efficiency, your home will lose heat through the roof. The result: the floor of the house will require a lot of heating, it will be difficult to maintain a comfortable temperature, and the rooms will have a humidity level above 50%. The signs you will see are mould on the walls, ceiling and woodwork, and an unpleasant smell in the air and on fabrics. To solve the damp problem, you will need to insulate the roof or attic space.

A leaking part of the roof

Damp may also be caused by a leaking roof due to broken or displaced tiles or a pierced gutter.

When floor insulation is defective, moisture can seep in from the ground up. One way to spot this is to look for the appearance of mould between floor tiles or at the base of walls. In this case, you will have to ensure that the foundations of your home has proper drainage and install a damp-proof course or even dig a trench around the base of walls of older properties.

Causes of humidity in walls and floors

Damp can occur for a variety of reasons:

• Natural rising water: a house may have been built over a water pocket, or a nearby water vein may generate damp. If this is the case, a perimeter drain should be installed or the foundations of the house may have to be sealed with a bitumen membrane or a primer.

• Rainwater: if the roof of a neighbouring building doesn’t have a gutter, or the gutter is damaged or too small, and the water from one side of the roof is pouring down the walls of your house, the rainwater drainage system needs to be reviewed. Damp may also come from rainwater which hits off the wall and infiltrates the structure via small cracks. The presence of hygroscopic salts in large amounts may explain a particularly high humidity rate. To combat water in the walls, you will have to dig into soaked areas and inject a damp treatment.

• Damaged and leaking pipes: water pipes may be leaking and causing a damp problem in the home. 

• Rendered exterior walls: on old buildings, render is sometimes found at the bottom of the exterior walls. This prevents water from draining out of the house, so the moisture escapes into the home. Removing the render should be enough to solve the problem, otherwise you can install a drain.

• Poorly waterproofed foundations: if the house, whether new or old, has poorly insulated foundations, the waterproofing of the foundations will have to be reviewed. To resolve this, a bitumen membrane must be applied, while the installation of an additional drain is also recommended.

Some materials are known to cause damp by reacting with other materials. A lot of materials used in older properties tend to hold water (such as render made from very alkaline cement). You will have to remove these elements to start drying out your walls properly.

Condensation in the home often appears in the form of water droplets on walls, windows and even furniture. This is caused by warm air that settles on cold surfaces and turns into water. The moist environment this creates can lead to mould growth which, in turn, can trigger respiratory problems or even aggravate joint pain!

To reduce humidity due to indoor condensation, it may be necessary to install an air vent system, to put an extractor fan in damp rooms, to opt for a cooker hood with a higher flow rate, to install a bathroom extractor fan and/or to air the house more frequently when the bathroom and/or kitchen are being used. Not heating the home sufficiently can also be a cause.

Poorly insulated homes contain points called thermal bridges. These are generally found around windows, patio doors, entryways and garage doors at the meeting point between surfaces (e.g. roof/wall or wall/ground). The difference in temperature at these points leads to a build up of moisture and heat loss which, in turn, costs you money.

Heating a room allows you to get rid of some of the water held in the air; basically, turning on your heating will reduce the level of humidity. The ideal scenario would be to maintain a constant temperature of at least 19 degrees. If a room is not heated overnight, water vapour from your breath and the warmth of your body will cause water to settle on the windows and walls.

On the other hand, heating your home excessively will dry out the air and cause other issues such as drying of the mucus membranes, headaches, or throat irritation. Choosing the right heating system (e.g. boiler, electric radiators, a wood-burning stove, etc.) is therefore essential.

Applying damp-proof paint will not solve damp problems.

Dehumidifiers draw in moist air from rooms in order to reduce the level of humidity. However, these can only be used for mild humidity issues. You should be aware that the use of a dehumidifier alone will not be enough to fight developing or established humidity issues.

Finally, dehumidifiers do not have any effect on the quality of the air. In other words, they do not make your air healthier to breathe. If you want to improve the quality of your air you will have to find the source of the humidity (groundwater, poor insulation, faulty heating, etc.) and think about setting up a Positive Input Ventilation (PIV) system.

PIVs generally allow you to save on heating (by around 10%) as it is cheaper to heat healthy, dry air.

Fighting humidity comes down to a set of preventative measures.

1. Air out your home twice a day to release warmer air and ventilate your bathroom after showering.

2. Avoid organic paints which can encourage mould or even mould mites.

3. Use your air conditioning system if you have one or install an air vent system.

4. Set up a Positive Input Ventilation (PIV) system.

5. Set up plans to reduce thermal bridging at doors and windows.

6. Upgrade your electric radiators for greater energy efficiency.

7. Lay a water-repellent seal over exterior joints.

8. In the kitchen, cover up your pots and use your cooker hood every time you cook.

9. Dry your laundry in a well ventilated room.

10. In the wintertime, do not forget to air out your home in order to release any stale air!

When replacing your windows, choose double-glazed windows with a built-in trickle vent to limit condensation.