Can you get a subsidy for a flat roof window? One number determines everything

Is a skylight or flat roof window part of your renovation plans? If so, you may be eligible for a grant in Flanders. But not every daylight product qualifies. One technical figure makes the difference.

A roof opening definitely counts

Many people only think of insulation when it comes to roof grants. Yet installing a roof opening, such as a flat roof window, a skylight or a sun tunnel, is clearly included in the list of works eligible for Mijn VerbouwPremie. You can submit the file under the windows and doors category, or under the roof category if you are also insulating your flat roof at the same time.

The threshold: maximum 1.0 W/m²K

To qualify, the U-value of your skylight or flat roof window must not exceed 1.0 W/m²K. This value indicates how much heat is lost per square metre. The lower, the better. It must also be determined according to the correct standard and in line with the CE marking: NBN EN 1873 for skylights and NBN EN 673 for the glazing.

That requirement is stricter than it may seem at first glance. A classic single-walled or double-walled polycarbonate skylight does not reach 1.0, and many triple-walled versions also remain above it. Anyone who has a cheap skylight installed assuming the grant will make up the difference will be disappointed when applying.

These Skylux solutions stay below the limit

• iWindow3 flat roof window. HR+++ triple glazing with a Ug value of 0.5 W/m²K. Well below the required value, and also the quietest solution in rain or hail.
• iWindow2 flat roof window. HR++ double glazing with a Ug value of 1.0 W/m²K. Exactly on the standard, with the sleek flat finish of the iWindow range.
• Five-walled plastic skylight. 0.99 W/m²K. If you prefer to stick with the classic dome shape, the five-walled version is the only one that meets the threshold.

You can find all technical data, models and dimensions on our page about the iWindow flat roof window.

For every daylight product you are considering, ask for the declared U-value and the standard on which it was calculated. A reputable manufacturer will provide that documentation without hesitation.

The practical conditions at a glance

• Since 1 March 2026, the highest and middle income categories can no longer apply for the grant for windows and doors. Nothing changes for categories 3 and 4.
• The works must be carried out by a contractor.
• The total invoice amount must be at least 1,000 euros excluding VAT per category of works.
• At the time of application, your invoices may be no more than 24 months old.
• After approval, a waiting period of five years applies for the same category of works. So it is better to combine your roof works rather than spread them out.

This information is a snapshot from August 2026. Grant conditions change regularly. Always consult mijnverbouwpremie.be for the current rules.