How to insulate an existing wall?

To insulate an existing wall, you are looking at 3 major options:

• external wall insulation
• interior wall insulation
• cavity wall insulation

Whichever method you choose, the insulation needs to be put in place with the greatest care. Poorly applied insulation may cause mould problems or 'thermal bridges’, i.e. points where the insulation barrier is interrupted.

Before you start applying insulation, be sure to seek out the best solution.

In the city, especially when you live in an apartment, it is easier to insulate an existing wall from the inside than from the outside. Nonetheless, stay on your guard as insulation from the inside may have disagreeable consequences if handled the wrong way.

Avoid inseeping moisture

The bond between the wall and the insulating material needs to be perfect and the wall needs to be completely sealed and waterproof. It also needs to resist rising damp and torrential rain. Get a professional in to make sure your home complies with applicable requirements before you start work.

How much should you expect to pay?

More than anything, the price to insulate an existing wall depends on the technique adopted and the materials chosen. On average, external wall insulation costs twice as much as interior wall insulation.
Some examples:

• you should reckon with around 150 € per m² for external wall insulation with a wood panelling finish;
• 70 € per m² for interior wall insulation using plastered wood fibre boards;
• insulating a cavity wall will cost you around 25 € per m²;

Different insulation techniques

Insulation from the outside

• Brick cladding
  on the exterior wall a wood fibre panel is applied, leaving a cavity, referred to as an air space, before a brick facing wall is put up. Do not leave an air space unless you are using a water-repellent (hydrophobic) material, such as cork, instead of wood fibre.
   
• Roughcast finish
  an insulating wood fibre panel is directly placed over the facing wall. On the panel comes a trellis and a render coat. Next, the roughcast is applied.
   
• Wood panelling finish
  insulating material (hemp, glass wool, cellulose acetate flakes, etc.) is fitted onto the wall, which is subsequently finished with a wood fibre panel. The final wood panelling is attached onto laths to leave an air space.

Insulation from the inside

• Plastered wood fibre boards
  wood fibre boards are fitted onto the interior wall, which are subsequently plastered. Panels exist that carry the NaturePlus label, as a guarantee of eco-friendly construction materials.
   
• Wood finish
  an insulation layer (hemp, flax, cellulose acetate flakes, etc.) is fitted onto the interior wall, and subsequently clad with a wood panel. The user can then add a natural or reinforced plasterboard as the finish of choice.
   
• Cavity wall insulation:
  Cavity walls also lend themselves to having insulation fitted. To do so, the wall cavity is filled with polystyrene beads, mineral wool or polyutherane foam through tiny holes made in the joints of your wall.