Breather Membranes
Shop breather membranes for pitched roofing from leading brands including Cromar, Klober, Permavent and Proctor. Choose from vapour-permeable and air-open roof underlays in a range of roll sizes for different roofing applications.
Frequently Asked Questions (4)
Generally, breather membranes allow water vapour to escape from inside a building without the need for extra ventilation.
The thickness of a breather membrane will all depend on the project type. For example, 135gsm thickness membrane will be suitable for more advanced roofing projects.
It is widely recommended to use breather membrane is most roofing projects. However, in unique situations a non-breather membrane is more suitable.
A vapour-permeable membrane allows water vapour to pass through the material. An air-open product is designed to permit both air and water vapour movement. These characteristics can affect how the underlay works within the roof's ventilation strategy, so check the technical information for the individual product.
Breather Membranes
Choosing the Right Breather Membrane
A breathable roof underlay sits beneath tiles or slates as part of a pitched roof system. It allows water vapour to pass through while providing a secondary barrier against moisture entering beneath the external roof covering.
The right product depends on the roof construction, required performance and installation method. Compare the technical specification rather than choosing by price or roll size alone.
Vapour-Permeable vs Air-Open Membranes
Although the terms are sometimes used interchangeably, breathable roofing products do not all perform in exactly the same way.
Vapour-permeable membranes allow water vapour to pass through the material. They are commonly used as underlays for pitched roofing.
Air-open membranes are designed to allow both air and water vapour to pass through. This can affect how the product is used within the overall roof ventilation strategy.
Always follow the manufacturer’s guidance for the specific product and roof construction.
Which Roof Membrane Do I Need?
Start with the specification and construction of your roof. Important factors include:
- Intended roofing application
- Required air and vapour permeability
- Supported or unsupported installation
- Wind exposure
- Roll width and length
- Required coverage
- Fixing and lap requirements
- Manufacturer guidance
Do not assume that two products with a similar weight or appearance provide the same performance.
What Does GSM Mean?
GSM means grams per square metre and indicates the weight of the material per unit area.
However, a higher GSM does not automatically make one membrane better or more suitable for a particular roof. Strength, water resistance, vapour permeability, air permeability, wind-uplift performance and the intended application should also be considered.
Use the complete technical specification when comparing products.
Choosing a Roll Size
Roof underlays are available in different widths and lengths, including popular 25m and 50m rolls.
Calculate the roof area first and then allow for the laps, detailing and installation requirements specified by the manufacturer. Wider rolls may reduce the number of horizontal laps, while smaller rolls can be more convenient for certain jobs.
Leading Roofing Membrane Brands
eRoofing stocks products from established manufacturers including Cromar, Klober, Permavent and Proctor.
The range includes Cromar Vent 3, Klober Permo and Permavent products, with options designed for different roofing requirements.
Compare the individual product specifications carefully to find a suitable underlay for your project.
What Should I Check Before Ordering?
Before choosing a product, check:
- Intended application
- Roof construction
- Air and vapour permeability
- Water resistance
- Roll dimensions
- Required coverage
- Installation and fixing requirements
- Manufacturer certification and technical guidance
Where a roof has a particular design specification, choose a product that meets those requirements rather than selecting on price or GSM alone.
