There are two ways to insulate a flat roof: with the insulation material under a new layer of roof covering (1) or with the insulation material on top of the existing roof covering (2).
1- Under the roof covering (‘warm roof’)
The best insulation is created by removing the existing roof covering. First a vapor barrier layer is placed on the flat roof and then the insulation panels. On top of this is added a new layer of roofing material (for example bitumen or EPDM). The roof edge may then need to be raised (to prevent rainwater from flowing or blowing over the roof edge).
2- On the roof covering (‘inverted roof’)
A second option is for the insulation company to place pressure-resistant, water-resistant insulation boards on top of the roof covering. On top of that, add a layer of gravel or tiles to prevent the panels from blowing away. With this approach, the existing roof covering must be in good condition, because it will remain in place. The final insulation value is slightly less good. Here too, the roof edge sometimes needs to be raised.
TIP From the inside: not recommended
Insulating a flat roof from the inside seems easier than from the outside. However, MilieuCentraal does not recommend insulating flat roofs from the inside. Moisture accumulation (on the inside of the roof) is difficult to prevent and can lead to mold and wood rot.
