DUKO (Dampspærre- og Undertagsklassifikationsordning ApS) is an independent Web-based information scheme whose purpose is to help developers and consultants choose the correct underlay or vapour control layer system.

DUKO provides an overview and makes it easier to find the underlay that suits your roof and building.
DUKO divides underlay products into different exposure classes and requires suppliers to submit documentation of the properties of their products. 
DUKO helps ensure correct installation, also by requiring manufacturers to prepare detailed instructions in how to use the different underlay products correctly.