ᐅ Request for insulation design proposal for ventilated roof underlay system needed

For builders and homeowners, the question arises as to whether roof insulation without a vapor retarder is still possible under the new standards. The answer depends on the insulation materials used: Roof insulation without an explicit vapor retarder is an option when capillary-active insulation materials are used, which can independently regulate the moisture balance of the roof.

Roof insulation without a vapor retarder – not yet a general standard
The technical requirements mean that today, a vapor retarder cannot be omitted in roof insulation. In ventilated or vented pitched roofs of previous decades, it was usually integrated into the roof structure via a waterproof, airtight, and vapor-tight bituminous roofing membrane above the roof sheathing. The ventilation on the outside and the insulated interior side ensured reliable removal of any moisture or water vapor that had entered. An interior vapor retarder was only necessary if ventilation was insufficient and/or to provide a greater drying capacity.