What is Breathable Roofing Membrane and How does it Work?

This blog holds key insight into the difference between non breathable and
breathable roofing membrane in today’s roofing industry.

What is Breathable Roofing Membrane?

Breathable membrane and non breathable roof membranes share the same primary function in preventing water ingress on roofs in aim to prevent damp and mould. Whilst both are completely resistant to the elements that a roof faces, the difference between the two is that breather membranes (also known as breathable membranes) are forms of house wrap that allow otherwise trapped vapour and condensation to ventilate from your roof. The functional qualities for breather membranes are:

1. To restrict any rain water that penetrates past the exterior finish
2. To perform as a breather material allowing any moisture trapped in the wall cavity
to escape
3. To act as a wind barrier to restrict movement of air through the wall

Breathable roof membranes are typically used in constructions where external cladding or tiles are not completely water-tight or resistant to moisture. The breather membrane is located on the cold side of a roof’s insulation – beneath the support for the tiles to prevent anything penetrating the structure. The three key performance areas for breather membranes are: resistance to water vapour, water vapour permeability and water tightness.

How and When Can You Use Breathable Membrane?

The popularity of breather membrane has excelled over recent years as it is a modern, lightweight alternative to traditional styles of underlay products such as 1F roof felt. There are many advantages for using breathable membranes when compared to alternatives as there is more choice surrounding performance and suitability.

Breather membranes have a lower total resistance to non breathable roof membranes as water vapour cannot travel through the material. As breathable roof membrane allows much more moisture to transfer into the batten space above, it is vital that there is sufficient air movement for any built up condensation to escape.

Non breathable, high resistance membrane is suitable in cold, ventilated, pitched roof systems – where as warm roofs without adequate ventilation require breathable membrane. Both types of roof membrane do however benefit from effective ventilation as water vapour is forced out of the roof of the house.

Another key element for preventing damp is the creation of a drainage cavity between cladding and wall sheathing. There is a fair likelihood that water can penetrate any roof tiling, so it’s important drainage is in place to allow any water that gets inside to naturally escape.

Our Recommendations

There is no ideal breathable roofing membrane for every given situation as it always depends on the roof’s characteristics. It’s impossible to design a membrane that excels in every department, and because of this, manufacturers cater to specific factors such as breathability, water tightness, vapour control, strength or durability.

This leaves you with an important decision to make based on your roof alone, so it’s vital to choose a membrane built for the specific problems that you may face over the short and long term. Influencing factors can be the location of the roof, its pitch, baton gauge and the type of tile used above the membrane.

If your roof faces a lot of wind uplift, you should buy a membrane that is stronger and more durable – often made to manage the elements comfortably. A perfect example is Cromar Vent 3 Classic , which has all the benefits of lighter membrane with a higher tensile strength.

On the other hand, your roof could be exposed to a high degree of condensation, so in this instance it would be more efficient to choose a highly breathable roof membrane that will successfully manage this problem. For a cheap option, we recommend Cromar Vent 3Light, as it is a breathable membrane that costs as little as £0.54 per square meter. On the opposite end of the spectrum are specialist products such as Klober Permo Air that offer superb quality at a premium price of £3.30 per square meter.

Using a membrane that is made from a high quality material can help in increasing the roof’s lifespan, particularly as certain brands and products offer full roof life guarantees. The
best membranes to purchase find the exact right balance between affordability, quality and thickness.

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