What is a membrane in roofing?

Roof membranes act as a secondary weatherproof barrier beneath the roof covering, helping to manage the movement of moisture while protecting the roof structure from wind-driven rain and snow. They are installed as a continuous layer beneath the roof battens as part of a standard roof construction.

Roofing membranes are a high-performance alternative to traditional roofing felt and are also referred to as roof underlay. It is specified in pitched roofs, hipped roofs, gable roofs and all other types of roofing system across the UK.

Does a roof need a membrane?

Roofing membrane, or underlay, is considered to be one of the most important elements of any roofing specification. It is an essential component of modern pitched roof construction and provides a range of benefits for the whole building.

These include:

• Weathertightness – A roof membrane will help your roof system resist water, wind and snow infiltration. These are some of the most common causes of cold and damp, making a roof membrane underlay vital for protecting the longevity of the home.
• Condensation control – A breathable roofing membrane also regulates the flow of water vapour from within the building. It allows water vapour to disperse without compromising the watertightness of your home.
• Improved wind loading – A correctly specified and installed roof membrane will take some of the wind loads imposed on the overall roof, thus reducing the impact of wind uplift on the roof tiles and fittings.
• Strength and safety – Modern roof membrane underlays contribute to the overall robustness of the roof system and help provide a safer work area once installed due to their higher tensile strength than the traditional bitumen-based felts they replaced.
• Durability – A roof membrane can extend the life of the roof system by making it more robust and weather-resistant.
  
  

Types of roofing membranes

The type of roofing membrane you choose will depend on your specific design. The two main types are breathable membranes and non-breathable membranes.

Breathable membranes

Breathable membranes are vapour permeable and the most common type of roofing membrane specified. Breathable membranes are typically:

• Lightweight
• Durable
• Easy to install
  
  

Depending on the roof design and condensation risk assessment in accordance with BS 5250, breathable membranes can reduce the level of roof ventilation required. However, they should not be installed without any ventilation. BS 5250 and NHBC guidance generally recommend that ventilation is provided at both eaves (low level) and ridge (high level) to ensure sufficient crossflow roof ventilation and optimum performance with a breathable membrane.

A breathable membrane will protect the home against the weather, and work in conjunction with ventilation to manage condensation build-up in the home.

Non-breathable membranes

Non-breathable membranes share many functions with breathable membranes, such as:

• Preventing water ingress
• Reducing the chances of damp and mould forming.
  
  

They should be used as part of an overall system along with traditional ventilation methods, such as roof vents and vapour control layers, to ensure adequate airflow in a roof system. Without this, damaging condensation is likely to build-up and adversely affect the roof and the home.

Discover Marley roof underlay membranes for every project and get technical assistance from our team.

Disclaimer - The information shared in this blog is correct at the time of publication. Guidance, standards, and best practices may change over time, so if you’d like further clarification or the latest updates, please get in touch with the Marley Technical Advisory Team, who will be happy to help.