Roofing Underlays and roofing membranes

Roof underlays for weather protection and condensation control

Roof underlays are also known as roofing membranes or felt. They form an important second line of defence for all tile and slate pitched roofs, providing protection against water ingress from wind-driven rain and snow. They also act as a temporary weather shield during roof construction, before installing the roof covering.

In addition to protecting against external moisture, the roof underlay can help to reduce the risk of condensation in the roof space.

Breathable vs non-breathable roof membranes

BS 5250 classifies underlays as breathable or non-breathable depending on their vapour resistance.

• Breathable roof underlays – Also called vapour-permeable or low-resistance (LR) underlays, these have a vapour resistance below 0.25 MNs/g. Water vapour can pass through them, but liquid water cannot. This means that they can contribute to roof ventilation and condensation management.
• Non-breathable roof underlays – Also called non-permeable or high-resistance (HR) felts, these have a vapour resistance above 0.25 MNs/g. They do not allow air, liquid water or water vapour to pass through.

The benefits of Marley roof membranes

• Breathable or non-breathable options
• Designed to meet the relevant requirements of BS 5534
• High resistance to water penetration
• Wind-uplift resistance for different exposure conditions
• High tensile and tear strength
• Integrated tape for sealing laps
• Printed guidance lines for more accurate positioning
• Lightweight and easy to handle
• UV resistant*
• BBA approved

*Although some UV resistance is built into the membranes, the roof covering should be installed as soon as possible to minimise any degradation and so it is not exposed at the eaves.

Choosing the right roofing underlay

Specifying the right underlay depends on the roof design. Considerations include the roof construction, pitch, primary roof covering, ventilation strategy and moisture management requirements, as well as location and wind exposure.

Marely’s range of roof underlays includes products to suit a wide range of applications. Technical information and support are available to help identify the right product for each project.

Marley roofing underlays

Marley roof underlays provide weather protection beneath pitched roof coverings. The range includes both breathable and non-breathable membranes for different roof constructions and moisture management requirements.

Products include:

• Vapour Permeable Underlay
• Non-breathable Underlay
• Universal 125 Vapour Permeable Underlay
  
  

All Marley roof underlays are designed to resist wind uplift, with high tensile and tear strength for durability. Depending on the product, options are available for UK zones 1–5, depending on the specification. They also include an integrated tape system that provides a convenient way to seal the laps and helps to reduce issues relating to wind uplift.

With Marley roofing underlays, there’s no need for laps to coincide with tile batten courses. This helps to make installation easier and quicker, reduces waste and improves cost efficiency.

Roof underlays from Marley

Marley offers a range of roofing underlays suitable for a wide range of applications. Products can be specified on their own or as part of the complete Marley Roof System.

For more information, explore our online resources:

• Read our blogs for practical information about the British Standards and specifying roof underlays.
• Browse our case studies for examples of Marley roof underlays being used in pitched roof projects including housing developments, private homes, social housing, schools and office buildings.
• Download technical information about roof underlays, including product data sheets, installation guidance and product certification.
  
  

For further advice, or to discuss your project in more detail, please contact our technical team.