Why insulate your dwelling house?

To reduce your heating bills and improve your comfort, thermal insulation in your home is very often the first thing to consider. Insulating your dwelling house is beneficial for your wallet and also for the environment because it helps to limit greenhouse gas emissions.

Successful insulation requires choosing suitable materials implemented by professionals or experienced DIY enthusiasts.

Several insulation techniques exist and knowing and understanding them will allow you to carry out your work with peace of mind.

Note that insulating roofs and walls significantly improves the energy performance of houses built before the appearance of thermal regulations. Renovating your house and providing thermal insulation is the guarantee of a good investment. Indeed, a well insulated and well ventilated house is much more pleasant to live in.

Over time, over time, your property will require much less maintenance if it is isolated. Insulation, combined with effective ventilation, will eliminate the risk of condensation causing damage to paintings, windows, walls ...

Comfort and energy savings are the values ​​of well-thought-out thermal insulation. In winter, the insulation will reduce heat loss through the walls and in summer will prevent outside heat from entering your dwelling house, thus resulting in a substantial reduction in your energy bill (heating and / or air conditioning) .

In winter, the poorly insulated walls (walls, windows and windows) are cooled by their contact with the outside air, thus causing a feeling of discomfort despite the hot air in the room in which we are; the perceived ambient temperature is then lower than the temperature displayed on your thermometer.

In summer, the uninsulated walls are heated by the outside air and make the room you are in warm and moist.

In your dwelling house or apartment building, properly carried out insulation and ventilation will eliminate this cold and / or hot wall effect.

Last but not least, thermal insulation will often improve sound insulation.

At the same temperature (the temperature displayed on your thermometer), a house, an apartment, and well-insulated offices offer greater comfort. At the time of sale or rental, your home benefits from a higher ranking in the Energy Performance Assessment. Good insulation coupled with good ventilation is the guarantee of better heritage value.

Let's come back to the feeling of a cold wall. A cold wall (poorly insulated) draws heat from your body. For example, a wall at 14 ° C and ambient air at 20 ° C (the number displayed on your thermometer) gives a perceived temperature of only 17 ° C. Figures that give food for thought about the relevance of your energy expenditure. But thermal insulation is not everything, too much air movement in a room also causes a feeling of discomfort. It is accepted that the air speed should not exceed 0.2 meters per second in winter. But beware, with air that is too saturated or too dry there is also a feeling of discomfort. To feel good, the humidity in a room should be between 35% and 60% relative humidity, no more and no less.

So ventilate well and always banish humidity, too many homes have humidity problems ... Insulation must always be associated with ventilation called CMV (Controlled Mechanical Ventilation) or double flow ventilation (which manages the incoming and outgoing flows of housing and recycles the air, which a CMV does not). In fact, homes always contain humidity induced by occupants, humidity that must be managed. The water vapor in the air in a home is always higher than that in the air outside.

At the same time, care must be taken to ensure that your premises are airtight, which may seem incompatible with renewing the air in a room, but not entirely. All this must be controlled ... On the one hand the renewal of the air, on the other the airtightness of the walls and openings (bays, windows, doors, etc.).

Doing one without doing the other is nonsense, which unfortunately too often is done for lack of information or resources (Changing the windows of a good without taking care of the ventilation leads to major humidity problems or even causes or promotes certain respiratory diseases - it is a poor response to a good diagnosis which calls into question the usefulness of the insulation work carried out).

It is therefore necessary to ensure airtightness (insulate) and regularly renew the air in a room (ventilate) and this work must be done in a thoughtful manner.

Here's how...

  1. Don't forget to treat thermal bridges

These are areas of weak insulation. The cold outside passes through it more quickly inside the home. Water vapor condenses on these colder spots, which can cause black streaks and mold to form. The most important thermal bridges are:

  • At the junctions between the roof and the walls,
  • Between the walls and the window frames,
  • Between floors and walls,
  • At the junction of the balcony and the wall,
  • At the level of the uprights of the frames, rafters, fixing points, etc.

A good continuity of the insulation and the waterproofing membrane (be careful, two separate elements) must allow these weak points to be treated and during work that you will do later in your home (extensions, creation of an opening, etc.) , care must be taken to respect the integrity of the insulation, to preserve its continuity so as not to create new thermal bridges.

What is a waterproofing membrane or vapor barrier?

Answer: The humidity emitted by a person is 40 to 200 g of water vapor per hour; a hot shower, 200 g per hour; a boiling saucepan, 400 g per hour.

In winter, when water vapor passes through a wall, it gradually cools from the inside to the outside. Sometimes it even condenses and becomes liquid water in the wall and causes serious damage (mold, peeling wallpaper, degradation of plaster, etc.).

The installation of a vapor barrier or a vapor barrier (a film that is always placed on the warm side of the room, that is to say on the side of the insulation located inside) during work insulation limits the accumulation of humidity behind the insulation.

Depending on the material of the walls, the transfer of moisture from one side to the other is more or less important. Insulation should never be carried out on a wall showing signs of dampness.

  1. Remember to complete important jobs with small, efficient jobs

What are these small jobs that will further reduce wastage?

  • Insulate your hot water tank (if it is not already by the manufacturer) and the hot water pipes that pass through unheated rooms (garages, etc.),
  • Insulate the roller shutter boxes,
  • Eliminate cold air passages under doors leading to unheated parts of the house (garage, cellar,
  • Close any unnecessary chimney.

These small, efficient jobs will help improve your comfort and reduce your heating needs.

  1. What level of performance to achieve? An indication of performance with DPE

Since January 2011, the result of the energy performance diagnosis (D. P. E.) appear in the content of real estate advertisements (for rent or for sale).

Thus, it is possible to have an approach to the consumption of heating, domestic hot water and / or air conditioning, on the basis of normal use of the premises, without forgetting the greenhouse gas emissions induced. by this consumption. The D. P. E. also includes some recommendations and advice in order to improve the energy performance of the said property.

The Mericom Archi team of architects can help you interpret this data and advise you in your work, don't hesitate ...

  1. Some figures to know before you start


  • The roof accounts for 25% to 30% of heat loss.
  • Walls represent 20% to 25% of heat loss.
  • Thermal bridges represent 5% to 10% of heat loss.
  • Leaks and unwanted air renewals represent 20% to 25% of heat loss.
  • Windows account for 10% to 15% of heat loss.
  • Low floors represent 7% to 10% of heat loss.

The government has set high performance levels to qualify for financial assistance (tax credit, zero-interest eco-loan, etc.). It is therefore advisable to call in a professional before you start and to be able to claim these aids, at Mericom we are here to help you ...

To achieve a high performance such as the Low-engergy Building Consumption level, renovation of all the points must be considered to be satisfactory. An energy audit (Mericom Archi) makes it possible to determine the specific solutions adapted to your building.

  1. Understand the characteristics of your insulation

Insulation does not conduct heat, that's what it is for. Their technical performances, for opaque walls (walls, floors and not glazing), are reflected by quantified coefficients which appear on the packaging of the products: the coefficient of thermal conductivity lambda L expresses the ability of the insulation to conduct heat. . The smaller L, the more insulating the material (conventional insulating materials have Ls between 0.025 and 0.050 W / m.K.

The thermal resistance R, expressed in m2.K / W, is obtained by the ratio of the thickness (in meters) to the thermal conductivity L of the material considered.

The thermal resistance of an insulating material will be all the more removed the greater its thickness and the lower its coefficient of conductivity.

Oops! It's a bit complicated ... Basically the R coefficient must have a high value and the L coefficient must have a low value.

  1. Points to recognize before carrying out your work

To dissipate the heat contained in a home, ventilation and solar protection of the windows are essential. The insulation of the walls and the roof is also. In fact, everything is essential.

The thicker the walls and the heavier the materials, the greater the inertia and, if the inertia is great, the heat will take longer to pass through your wall and warm your home.

Good cold insulation does not guarantee a comfortable home in July or August. For example, insulation carried out from the inside does not benefit from the inertia of the walls, on the contrary an ITE (External Thermal insulation) - see the Mericom video) will benefit from the inertia of the walls.

Eh yes ! We want to keep our accommodation cool in August ...

  1. Require one of the certified products. Why ?

Certifications attest to the conformity of products to designated characteristics. They are always issued by independent organizations and are therefore a guarantee of quality.

There are also independent labels that rely on private voluntary initiatives. They are not framed by regulatory provisions and do not have the obligation to comply with independent controls. Their quality varies according to the seriousness of those who promote them.

Up to you ! We keep in touch ...

The CE mark simply indicates that the insulation meets the requirements of the European Construction Products Directive. Please note, this marking is not a mark allowing the products to be classified qualitatively.

The Keymark is a voluntary European certification mark demonstrating compliance with the European standard. It belongs to CEN, the European Committee for Standardization, and to CENELEC, the European Committee for Electrotechnical Standardization. The Keymark indicates that the product meets all the requirements of the standard.

The NF or CST Bat certification applies to load-bearing insulation materials such as cellular concrete, bricks or terracotta monomur.

That's it ... or almost ... for today;

  1. The impact of products on the environment and health

First of all, let's say that all insulation products have an impact on the environment and currently we do not have a benchmark scale allowing products to be classified according to environmental criteria. No document or recognized standard allows a product to be qualified as an eco-product, eco-material or ecological material.

Insulators may contain toxic substances (volatile organic compounds in insulating foams, pesticides in certain bio-based insulations, particles and fibers from mineral, plant or animal wool, etc.).

There is labeling on construction products indicating the level of volatile organic compound emissions from construction products and wall, floor or ceiling coverings, as well as insulation, varnishes, glues, adhesives ...

However, bio-based insulation is our preference. These insulators are made from renewable raw materials of plant or animal origin (Oops! So not necessarily vegan): wood, straw, cork, hemp, linen, feather, wool ... They have been processed and often contain a part of non-bio based materials or additives necessary for their conservation. They nevertheless have interesting characteristics, and are the very example of a promising progress. They are the subject of an increasing number of evaluations to test their technical performance.

To be continued ...


A propos de l'auteur


Architecte senior et CEO de Mericom

Architect in Nantes

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