Breathable membranes allow more water vapour to pass through than traditional bituminous felt. The complete roof design still determines whether additional ventilation is required.
Underlays for Moisture Control Beneath Roof Coverings
The layer beneath tiles or slates provides temporary weather protection during work and a secondary route for wind-driven moisture afterwards. MacBlair stocks roofing underlays and membranes for pitched roof construction and repair.
Choose by roof build-up, pitch, ventilation strategy and exposure, not roll colour alone. Vapour-open membranes and more traditional felts manage moisture differently, and every product has stated lap, drape, support and wind-uplift requirements. Printed lines are guides only when they match the required overlap.
Lay the underlay to shed water towards the eaves without obstructing designed airflow. Fix it beneath correctly spaced graded tile battens, then install compatible slates or roof tiles. Penetrations, abutments and repairs need the specified tapes or seals, with roof ventilation maintained throughout.
Roofing Felts Membranes FAQ's
Install the printed or stated face in the direction shown by the manufacturer. Orientation affects laps, water shedding and any integrated tape.
Lap dimensions depend on product, pitch and whether the joint is supported. Follow the roll markings only where they agree with the installation instructions.
Only for the temporary exposure period stated by the manufacturer. Cover it promptly because sunlight, wind and site damage can reduce performance.
Use the manufacturer's approved repair tape or patch method. Large or badly positioned damage may require replacing a section rather than applying a small patch.