Building
What is a Roofing Membrane (Underlay)?
A roofing membrane, also known as an underlay, is a vital component of a pitched roof system. Installed beneath the primary roof covering, it provides temporary weather protection during construction and acts as a secondary barrier against wind-driven rain, snow and dust once the roof is complete.
Roofing membranes also play a key role in moisture management by allowing water vapour to escape while helping to reduce the risk of condensation within the roof structure. In addition, they help control wind pressures beneath the roof covering, improving the overall performance and security of slates and tiles.
Membrane Construction
Our roofing membranes are manufactured using multiple layers to deliver strength, durability and high performance:
- Outer layer - A spunbond polypropylene (PP) or polyethylene (PE) layer that provides UV resistance and excellent mechanical strength.
- Functional core - A high-performance microporous or monolithic (hydrophilic) film that enables water vapour to pass through while preventing water ingress.
- Inner layer - A second spunbond PP or PE layer that enhances structural integrity and provides additional protection.
All Ubbink roofing membranes are rigorously tested to BS EN 13859-1 and are designed to support compliance with BS 5250:2021 for the management of condensation in buildings and BS 5534:2014+A2:2018 for wind uplift performance.
MultiVap Plus - 1m x 50m
MultiVap Plus is a vapour-permeable, highly water resistant, three-layer membrane featuring a PP spunbond membrane and microporous film. Designed for application to the outside (cold side) of pitched roof constructions, it provides effective protection against external moisture, while allowing water vapour from inside the building to escape.
Key Features
- Vapour-permeable and highly water resistant
- UV-resistant for up to 3 months
- Marking stripes for precise positioning
- High tear resistance
MultiVap Super - 1m x 50m
MultiVap Super is a strong, vapour-permeable and highly water resistant, three-layer membrane featuring a PP spunbond membrane and microporous film. Applied to the outside (cold side) of pitched roof constructions, it helps protect the building fabric from external moisture, while allowing water vapour from inside to escape safely. This combination helps ensure the roof structure remains protected, dry, and well ventilated.
Key Features
- Vapour-permeable and highly water resistant
- UV-resistant for up to 3 months
- Marking stripes for precise positioning
- High tear resistance
Choosing the Right Membrane for Your Wind Zone
Following new research into the wind loads experienced by roofing underlays and tiles, BS 5534 introduced a UK map dividing the country into five wind zones. While membranes are often categorised by their weight (gsm), wind zone performance is the key requirement for BS 5534 compliance. Use the guide below to select the appropriate Ubbink membrane for your project's wind zone.
MultiVap Plus
Suitable for Wind Zones 1–3 150gsm
Designed for use in low to moderate wind exposure areas, providing reliable protection and vapour permeability for a wide range of pitched roof applications.
MultiVap Super
Suitable for Wind Zones 1–4 170gsm
Our highest performing membrane, offering enhanced durability and wind uplift performance, making it suitable for all UK wind zones, including the most exposed locations.
Roofing membranes
Take a look at our Frequently asked questions about our membranes.
Yes. Roofing membranes should comply with the relevant British Standards to help meet UK Building Regulations.
Our MultiVap Plus and MultiVap Super membranes are tested to BS EN 13859-1, achieving UKCA and CE certification. They also support compliance with:
Our MultiVap Plus and MultiVap Super membranes are tested to BS EN 13859-1, achieving UKCA and CE certification. They also support compliance with:
- BS 5250:2021 – Management of moisture in buildings
- BS 5534:2018 – Slating and tiling for pitched roofs and vertical cladding
Roofing membranes are designed to provide temporary weather protection during construction. However, they should not be left exposed for longer than the period specified in the installation instructions, as prolonged exposure to UV light and the elements can affect performance. Always install the final roof covering as soon as practicable which is advised to be no more than 12 weeks, in accordance with STA Advice Note 18.
Vapour permeable roofing membranes are commonly used in modern pitched roof construction because they allow water vapour to escape from the roof structure while preventing the ingress of wind-driven rain and snow. This helps reduce the risk of condensation and contributes to a healthier, more durable roof system. The correct membrane should always be selected based on the roof design and in accordance with the relevant British Standards.
The correct membrane depends on your project's wind zone requirements, as defined by BS 5534.
- MultiVap Plus – Suitable for Wind Zones 1–3 (150gsm)
- MultiVap Super – Suitable for Wind Zones 1–4 (170gsm)
For help with installation please head to our Membrane Brand page.
UKCA and CE markings demonstrate that a product has been tested and assessed against the applicable performance requirements. For roofing membranes, this includes testing to BS EN 13859-1, giving specifiers, contractors, and homeowners confidence that the product meets recognised quality and performance standards.
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