Home insulation in Brussels, Flanders and Wallonia

Where to start?

Heat rises: in an uninsulated house, the roof is generally the main source of heat loss and the most cost-effective job. Walls come next, then floors or the cellar ceiling. Windows and airtightness complete the picture. And ventilation must not be forgotten.

The ideal order does depend on your house, though: an already insulated roof, cavity walls that are easy to fill or a cold cellar under the living room all change the priorities. An energy audit, sometimes required for grants (and, in Flanders, linked to the EPC and the renovation obligation after a purchase), helps set out a coherent plan. The adviser starts from your actual situation rather than a standard template.

The main techniques

In the roof, you can insulate from the inside between and below the rafters, from the outside (sarking) when re-roofing, or simply on the attic floor if the space is not lived in. Cavity walls can be quickly filled by injecting insulation; solid walls are insulated from the outside or, failing that, from the inside.

For floors, insulating the cellar ceiling with spray or boards is often the simplest solution. On a concrete slab, the screed generally has to be relaid. For good results, the target performance is around a U-value of 0.24 W/m²K for roofs and walls.

Damp, ventilation and grants

A better insulated house is also more airtight. You therefore need a carefully fitted vapour barrier, treated thermal bridges and sufficient ventilation to prevent condensation and mould. A good contractor covers these points in the quote, not just the insulation thickness. Proper ventilation also keeps indoor air healthy.

Insulation grants depend on the region, the part of the house insulated and your income, with minimum thermal resistance requirements. They change regularly, as the 2026 revisions to Mijn VerbouwPremie in Flanders showed: your RhinoEnergy adviser calculates them with you and checks the conditions before work starts. Some schemes require a prior energy audit or certified materials, which you need to know before signing.