How to choose building membranes: contractor guide for vapor control

A thermal insulation layer is only as durable as the moisture management surrounding it. In pitched roofs and ventilated attic assemblies, warm internal air carries vapor that condenses if it penetrates the mineral wool. Conversely, external wind-driven rain and tile condensation must escape outward without dampening the insulation.

The two-sided protection principle

Moisture safety requires two distinct membrane layers:

1. Warm side (interior): A vapor barrier to restrict moist room air from entering the thermal insulation layer.

2. Cold side (exterior): A vapor-permeable, breathable underlay that sheds exterior water while allowing trapped humidity to diffuse out.

BK45 and BD70 specifications

BK45 and BD70 are EuConX own-brand budget membranes, specified for Hungarian EKR projects. For quality-focused buyers we also offer BBarrier 90 g/m² and heavier membranes.

• BK45 (45 g/m² vapour barrier, Sd 30 m): Installed on the heated interior side of attic joists and partition walls as a vapour barrier.
• BD70 (70 g/m² breathable underlay, Sd 0.2 m): Installed on the cold exterior side to protect against draft and wind-washed water droplets while ensuring vapor permeability.

In typical EKR attic packages, 25 cm of ODE Starflex glasswool (2 × 12.5 cm) is paired directly with BK45 and BD70 for a complete installation package.

For technical data sheets, full roll dimensions, and direct project pricing, reach out at info@euconx.com or call +36 30 485 0258.