A cob wall must manage several flows: airtightness, heat, and humidity. But in construction or renovation, it is not always easy to provide a solution that respects the capabilities of the material.
So, how to insulate a cob wall? The main thing when insulating cob walls is to respect their natural humidity regulation. This is why hemp is a perfectly suitable insulator. Explanations.
Insulating a cob wall: characteristics to respect
Over time and depending on the weather conditions in the region, the cob can degrade more or less quickly. The key to keeping it upright is to ensure that water does not stagnate at the bottom of the wall or be retained by the use of poor material.
Unfortunately, this is often the case in renovations of old buildings: due to a lack of knowledge of “natural” products and materials, it is not uncommon to see the collapse of a cob wall due to the installation of insulation that suffocated it (cement for example). This is why the choice of materials that support and accompany a cob wall should not be taken lightly.
In this case, how to insulate a cob wall? Essentially, you just need to make the right choice of insulation. For this, it is essential to know the characteristics of cob:
- Very good hygrometric regulation: the cob absorbs humidity and makes the habitat breathe. It is not recommended to combine it with insulation that is sensitive to humidity.
- Charming aesthetic: combined with wood, cob offers a charming appearance to your exterior. It would be a shame not to take advantage of this by choosing the technique of exterior insulation.
- Controlled carbon footprint: Cob requires neither processing nor transport. It is approaching carbon neutrality. To remain eco-responsible, do not use synthetic insulation.
You now know that to insulate a cob wall, you must choose insulation that is not afraid of rain or humidity and can be installed indoors without suffocating the cob.
How to insulate a cob wall: what material to use?
We just said it: to insulate a cob wall, it is necessary to find a thermal insulator that is not afraid of water, but also does not repel humidity. Indeed, choosing permeable insulation exposes your home to condensation and therefore to the deterioration of the walls. In this case, which thermal insulation meets these conditions of use?
Hemp seems to be the solution. And for good reason, it offers the following advantages:
- Low thermal conductivity (0.039 to 0.050 W/mK),
- Absorbs humidity and releases it when indoor air is dry
- Good thermal and acoustic protection, whatever the season
- Produced locally (in France or Europe)
So, to insulate a cob wall, it is entirely possible to combine it with hemp panels. Both efficient and natural, this solution allows you to maintain a natural appearance and composition, even during renovation.
What is a cob?
Cob is a traditional building material, used to bind the stones of a wall or to fill gaps in the walls of a half-timbered house.
As a general rule, to successfully compose a cob, basic ratios must be respected:
- 3 shares of land
- 4 parts of straw
- 1 part sand (i.e. the color of the sand determines the color of the coating)
So, a cob is a mixture of straw, earth, sand, and water. You can also add wood chips to lighten it. Natural, renewable, recyclable, and healthy, cob has many advantages. In addition, the cob offers good thermal provisions (between 0.050 and 0.060 W/mK).
In addition to its easy maintenance, it fits defects perfectly and is not as fragile as cement. It is also economically interesting and is also accessible to implement.
Read also: How to Insulate Walls From The Inside?