How to Insulate a Damp Room? Easily

How to Insulate a Damp Room: Does a wall in your house feel damp to the touch? Have you observed signs of mold or infiltration? We must act.

To protect yourself from the consequences on your health or the good condition of the home, a damp room must be sanitized and insulated.

How to identify the reason and what are the possible solutions to deal with humidity? What materials should I use to reinforce the insulation of a wall? I am giving you his advice for staying dry.

Table of Contents

The essential– How to Insulate a Damp Room

Humidity in a home can have various causes: infiltration, rising capillaries, or leaks.

It is important to identify the reasons to find the right solution: this is the role of humidity diagnosis, carried out by a professional.

Certain insulators reinforce the resistance of a wall to humidity: mineral wool (rock or glass), hemp or sheep wool, or even cork and expanded polystyrene.

Read also: How to Insulate a Millhouse?

The different humidity problems

A stubborn odor, a spreading mold stain, condensation on the walls or furniture… In the rooms of the house, humidity is signaled in different ways. 

Before embarking on insulation work, it is essential to identify the origin of this abnormally high humidity. Several scenarios can be considered.

Capillary rise (rising damp)

This happens when moisture rises from the ground into buried walls. Porous materials draw water from the ground by capillary action.

Capillary rise leads to the formation of mold or condensation, particularly on the bottom of the walls. Wallpapers are peeling off and paints are blistering. Whitish deposits, containing saltpeter, are sometimes visible.

This humidity is most often generalized: it extends to the walls of several rooms in the house. [How to Insulate a Damp Room]

Water infiltration

Water seeps into the walls thanks to a crack, a blocked gutter, or even a waterproofing defect.

This problem is often confused with rising hair. To differentiate them, you can remember that the effects of infiltration are observed both at the bottom of the wall and at the height, of the ceiling or the joinery. But they are often limited to the room affected by the infiltration.

Read also: How to Insulate a Stone House? Easy Tips And Tricks

The condensation

This phenomenon occurs when the humidity level in the air exceeds 65% and ventilation is not sufficient.

When it comes into contact with a colder surface, the water vapor contained in the air deposits a film of water on the windows, furniture, or even walls.

This situation is favored by poor air circulation insufficient thermal insulation, or when the indoor temperature is too high. It affects a utility room (bathroom, kitchen) as well as the living room or bedrooms.

Leaks in pipes and pipes

Stains on the walls or ceiling, odors, or leakage can also be a sign of a leak in the building’s piping: cracks, poor connection, wear of joints or ends, etc. These symptoms are most often localized. [How to Insulate a Damp Room]

Construction humidity

In renovation as in construction, drying time is necessary so that the materials can evacuate residual humidity. This can take up to 12 to 18 months for a new building.

When drying is not done properly, the walls become damp, which encourages the development of fungus.

Why is it absolutely necessary to insulate a damp wall?

Damp walls represent a health risk for the occupants of the home. They can also have effects on the building itself.

Read also: How to Insulate a Container House?

Consequences on the health and comfort of residents

  • Exposure to mold and saltpeter increases the risk of developing allergies, respiratory illnesses, or infections. Fragile people are particularly concerned: children, seniors, people who are already ill.
  • Other problems can occur on a daily basis: headaches, sleep problems, irritation of the eyes, throat, or nose, nausea, etc.
  • Bad odors and the feeling of humidity cause discomfort. A damp home is also more difficult to heat, which leads to higher energy bills.

An impact on the condition of the building and its value

  • Walls, floors, or ceilings are weakened. In the long term, this reduces the stability of the building.
  • Fungi or the development of damp stains damage coatings and paints. This implies an additional cost when renovating.
  • A house that has waterproofing and insulation defects loses its value when sold or rented. [How to Insulate a Damp Room]

Insulate a wall in the presence of humidity

Insulation is one of the most commonly used solutions to combat problems caused by humidity. Easy to install, the simple insulation of a wall can be the solution in certain (few) cases but must be prohibited in many other cases: the insulation must be accompanied by one or more other interventions guaranteeing an effective and lasting result.

How to Insulate a Damp Room
Insulate a wall

Insulate with humid ambient air

In the case where the ambient air is overloaded with humidity (a rate greater than 65%), the insulation will make it possible to reduce or even eliminate the condensation of water vapor at the level of thermal bridges. 

In fact, it is at the cold spots in a room that the humidity in the air will tend to condense: on a single-glazed window, at floor level, etc. For homes suffering from ventilation that is not sufficiently efficient, insulation must be supplemented by the installation of a system guaranteeing air renewal. 

Otherwise, ambient humidity will cause the development of mold and fungus in your home. The feeling of comfort will not be there and you will probably wonder about the benefit of having your home insulated. [How to Insulate a Damp Room]

Insulate with a damp wall

All experts are unanimous: You should definitely not insulate a wall as long as it is damp. The wall must first be sanitized. Insulation would be completely ineffective and could increase humidity problems. It is therefore essential to take the humidity of the wall into consideration before starting an insulation project.

Soft insulation and humidity

By flexible insulation, we mean wood wool, glass wool, rock wool, hemp wool, cellulose wadding, etc. In the presence of humidity, these insulators will absorb it. They will become waterlogged, and quickly they will collapse. Humidity will cause the loss of their insulating power.

Rigid insulation and humidity

This concerns polystyrene panel insulation, whether expanded or extruded. These insulators could mask the humidity problem in the walls because polystyrene does not react or react very little to humidity. However, their use can make the problem worse. 

In fact, these insulators greatly limit the evaporation of humidity from the wall. Thus, this type of insulation causes an increase in the humidity level in the wall and accelerates its degradation.

Thin Insulators and Moisture

Thin insulation, also called multi-layer insulation, is made up of one or more layers of aluminum sheets or plastic film with aluminum with intermediate layers of different types. This succession of layers hides the humidity problem in the same way as rigid insulation. Aluminum sheets keep moisture in the wall. 

Their use can therefore worsen the problem. As you will have understood, be careful about suggestions for moisture-resistant insulation. Yes, the insulation will remain intact but not your wall, quite the contrary. [How to Insulate a Damp Room]

High-performance insulation

According to the rules of the art, for insulation to be durable and effective, it must be associated with water and airtightness of the walls. It is necessary to ensure that the wall to be insulated is indeed sound. In fact,  if your wall is healthy and dry, it is the primary insulator of your home.

Therefore, when the wall is damp and before carrying out thermal insulation work, it is necessary to identify the origin of this humidity,  treat it, and wait for the wall to return to a humidity level ” normal “. 

If the insulation work is carried out hastily, that is to say without waiting for the wall to dry, the insulation could lose its effectiveness by absorbing residual humidity from the wall. On the other hand, if this deadline is respected, you can renovate and insulate as you wish.

Why and How to Dry a damp wall before renovation?

So, after having treated the humidity in your wall, you will have the opportunity to choose the insulation that suits you.

By insulating your home as best as possible, you will improve your quality of life (heat in winter and coolness in summer) but also make significant savings by minimizing heat loss.

The icing on the cake is that insulating a damp wall while respecting the rules will add value to your property. Installing qualitative and durable insulation will bring real added value to your home: think about the impact on the energy performance diagnosis (EPD). [How to Insulate a Damp Room]

Read also: How to insulate your house naturally?

Which insulation is best resistant to humidity?

Not all insulation is created equal when it comes to water resistance. Wood wool or cellulose wadding in particular tends to absorb it: high humidity reduces their insulating performance. 

Here are 5 insulators best suited to insulating your walls while regulating humidity.

Rock wool and glass wool

These two mineral insulators have good water vapor permeability.

Installation of semi-rigid panels allows insulation from the inside by maintaining an air space between the wall and the insulation, for better ventilation.

Hemp wool

Formed from hemp fibers, hemp wool has characteristics equivalent to those of mineral wool. It is also more expensive.

But it has the advantage of being natural: a good point if you want to focus on more ecological work.

Expanded cork

This insulation offers good resistance to humidity. It is light and easy to use, but its price is higher than rock or glass wool.

In the form of a thin sheet, expanded cork can be used for thermal insulation of walls from the inside: performance varies depending on the thickness of the sheet. [How to Insulate a Damp Room]

Sheep’s wool

This insulation, made from animal wool, is rot-proof: it is a natural humidity regulator.

Sheep’s wool comes in the form of panels or rolls and can be used to insulate a damp wall.


Expanded polystyrene is most often used in the form of panels to insulate walls from the inside or outside.

Lightweight and durable, it does not absorb water and effectively resists humidity.

Which professional should I contact for the insulation of a damp room?

A waterproofing professional or a plumber can intervene to carry out a humidity diagnosis and help you identify the operations to be carried out. Depending on the type of work you need to carry out in the house, several craftsmen or companies can be contacted:

  • A plumber in the event of a leak in the house;
  • A mason to correct defects or cracks, apply a water-repellent treatment to a facade, or work on the structure of the building;
  • A plasterer for interior thermal insulation work;
  • A craftsman specializing in waterproofing to carry out external insulation.

Regardless of the professional, I recommend that you request several quotes to compete and benefit from the best price. You can also make sure that the craftsman is qualified for this work:

  • RGE (Recognized Guarantor of the Environment) certification allows you to benefit from state aid for energy renovation of your home;
  • The Qualibat qualification identifies professionals recognized in their sector of activity. [How to Insulate a Damp Room]

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