The ISDE is the national scheme through which the government supports insulation measures in existing homes. For roof insulation, it is an amount per square metre, and that amount doubles if you take more than one measure.
The scheme changes in the details almost every year. What is set out below is the situation in 2026; always check the current conditions with RVO before you apply.
The amounts in 2026
One measure: 16.25 euros per square metre. You insulate only the roof and nothing else. Then the basic amount applies.
Two measures: 32.50 euros per square metre. If you carry out a second insulation measure within twenty-four months, for example floor, wall or glazing insulation, the basic amount is doubled. This is the biggest lever in the whole scheme.
Bio-based: 5 euros per square metre extra. With insulation material of bio-based origin, such as wood fibre or sheep's wool, a supplement is added on top of the amount.
Maximum 200 square metres. Anything above that area isn't covered by the grant. With large roofs, that is a real ceiling.
“Doubling for two measures is the most important rule of the whole grant. If you only do the roof, you leave half of it on the table.”
Fouad, owner of Astrodak Service
The conditions where it gets stuck
Minimum 20 square metres. Below that area you don't qualify. With a small roof surface, that is a real threshold.
Rd value of at least 3.5 m²K/W. The insulation material installed must reach that value. In practice that means a generously thick layer; adding a thin extra layer doesn't qualify.
Carried out by a professional. Insulating yourself isn't covered by the grant. You need an invoice from a company showing the material, the area and the Rd value.
Owner-occupier of an existing home. The scheme is for owner-occupiers; new builds are excluded and a different route applies to landlords.
What does insulating get you in your own house?
The benefit depends on the roof structure, the current insulation and how you use the space. I work it out for you in concrete terms during the inspection, including the grant you are entitled to.
When to apply
After the work, not before. That is different from some other schemes, and it is a point where people trip up. You have the work done, you receive the invoice, and then you submit the application. The deadline is twenty-four months after the first measure was carried out.
That twenty-four-month period is also exactly the window in which your second measure has to fall to get the doubled amount. So if you insulate the roof this year and the floor next year, you still qualify for the higher amount. That is worth planning for.
What we put on the invoice
For an application you need details that must be on the invoice: which material was used, how many square metres, and what Rd value that material has. We include this as standard, together with the date of the work and our company details.
That sounds like an administrative detail, and it is the reason applications are sometimes rejected. Ask every company about it, because having an invoice changed afterwards is a tiresome process.
Municipal and provincial schemes
Besides the ISDE grant, some municipalities have their own funds for making homes more sustainable, and there are loans at a favourable interest rate through the Warmtefonds. These can sometimes be combined with the ISDE grant and sometimes not, and the conditions differ per municipality.
Why you should plan the second measure
Doubling for two measures within twenty-four months is the biggest lever in the scheme, and the window is wide enough to plan. If you insulate the roof this year, you have until two years later to tackle the floor or the glazing, for example.
In practice, that means it pays to think in advance about which second measure you were going to do anyway, even if it won't come up until next year. If you only do the roof and leave it at that, you leave half of the grant amount on the table for no reason.
Frequently asked questions about grants for roof insulation
