You are here: Home / Technical Tools & Info / For Architects / Comparison: Derbigum & Inverted Roofs

Comparison: Derbigum & Inverted Roofs

Inverted roofs

Warm/Derbigum roofs
The most used around the world





In case of a leak, repair procedures are more difficult and therefore   more expensive. Especially upstand details, roof outlets and where the   waterproofing are less accessible.

Since the membrane is exposed the leaks can   be easily identified and repaired. Maintenance minimal.

Insulation Choice

Limited Insulation choice: There is only   one choice for insulation panels: extruded   polystyrene (XPS).

Unlimited choice of insulation

Water Stagnation

Some quantities of water may be trapped   between insulation and waterproofing layer. Slopes should be constructed with   utmost care. Allow for a slope of at least 2%.

Water proofed at the first level - Water   un-penetrable through to the insulation

Insulation performance

Lower - As the XPS insulation boards are   vulnerable to be surrounded by hot air or by rainwater, reducing insulation   efficiency. Diffusion-tight covering layers can lead to increased moisture   content in the insulation, and wet insulation results in significant heat   loss. Additional heat is withdrawn by the water flow beneath the insulation   boards. Preventively increase calculated insulation thickness by 10%, because   of loss of heat.

Insulation performance remains unchanged.


HEAVY ROOF: Weight of ballast required to   keep the insulation may not be acceptable for static reasons.

LIGHT ROOF: A warm roof permits a lighter   roof structure.


For lower quality waterproofing membranes,   protection may be required.

The top range of DERBIGUM waterproofing   membranes have a proven durability of over 30 years on exposed roofs.  They are 100% UV resistant and do therefor   not require a protection layer.

Efficiency and Ecology

For high energy consuming buildings,   inverted roofs are not suitable to be used as a “passive cooler” due to the   lower reflectivity values of the ballast layer (gravel or concrete tiles).

Energy saving - By using a highly   reflective DERBIBRITE NT exposed membrane (in a warm roof construction), a   considerable energy saving can be reached on the cooling consumption. This   saving can be estimated via a roof energy audit.