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Which Roofing Underlay Do I need- Non-Breather or Breathable Membrane?

Wednesday, 26th September 2018

moisture release from permeable membrane

To breathe or not to breathe, that is the question. While we cannot tell you what materials were used on the House of Capulet in late 16th century Verona, we can explain the crucial differences between the breathable membrane and non-breathable membrane used in today's roofing industry.

Breathable membrane and non-breathable membrane share the same primary function of preventing water ingress on a pitched roof, reducing the chances of damp and mould forming.

Both are also resistant to wind and snow, qualities that will be put to the test for the remainder of 2018 if we are to believe early reports of a coldest UK winter on record.

The main difference between non-breathable and breathable roof membrane surrounds ventilation and how each tackles the problem of condensation- an issue prevalent in modern buildings which have greater insulation levels than ever before.

tyvek breathable membrane for pitched roofs

Located on the cold side of a pitched roof's insulation and beneath the battens which support the tile or slate, breathable roof membrane, as the name suggests, lets a building to breathe by allowing moisture to escape up through it and out of the building.

Non-breathable membrane on the other hand is not air permeable. This is not to say that non-breathable membrane is not suitable for new builds as non-breather membrane is still widely used and perfectly suitable on roofs where effective ventilation is already in situ.

So, in what circumstances are breathable membrane and non-breathable membrane suitable or unsuitable? Here’s what you need to know. (To see 6 of our top product recommendations, scroll to the bottom of this blog)

What Roofing Membrane Should You Go For?

breathable membrane installed under battens and tiles

Breathable membrane (low resistance) and non-breathable membrane (high resistance) are modern, lightweight underlay alternatives to the traditional bituminous type 1F products of yore.

Breathable roof membrane is the newer of the two underlays and the one whose popularity has soared in recent years. Before this, low resistance underlay was widely used in combination with a high/low ventilation system, primarily in the form of eaves vents and ridge vents.

However, this does not mean that roof breather membrane should be used as the sole means of ventilation. Although some manufacturers claim this with certain products and have carried out independent testing to prove so, these claims are not recognised by BS5250.

The low and high water vapour resistance tags given to breathable and non-breathable membrane respectively are classified so by British Standards.

klober non breathable membrane

Breathable membrane allows vapour to travel through it easier, while non-breathable doesn’t. In principle, the lower the water vapour resistance, the greater the membrane’s ability to lower the risk of condensation.

When non-breathable membrane is used below the slates or tiles, very little moisture makes its way into the batten space above. Roof breather membrane on the other hand allows far greater moisture transfer- making it crucial that there is adequate air movement above. 

Although it can be made air permeable to some degree, high resistance membrane is only suitable for use in cold ventilated pitched roof systems. Warm roofs, or roofs without adequate ventilation, require breather membrane, although again the breather membrane should not strictly be used in isolation in accordance with BS5250.

Non-breathable membrane can often be confused with a vapour control layer, but shouldn’t be. Vapour control layers are positioned on the warm side of the insulation to prevent large volumes of water vapour entering the roof structure from the interior, while also helping reduce heat loss through the roof. Non-breathable membrane is located on the cold side of the insulation.

water vapour barrier

Be it breathable membrane or non-breathable membrane, effort should be made to maximise any opportunity to improve roof ventilation to reduce the chances of condensation. Read our blog 'Eliminate Condensation In Loft With Roof Ventilation' for more ideas.

Resistance to wind and tearing are other important considerations. This performance will almost always depend on the quality of the material used. Lifespan is an important factor for any designer to bear in mind, with Tyvek breather membrane a prime example of a durable membrane.

Some underlays will only be compliant with certain wind zones as outlined in BS5534. Thickness gives a good indication of resistance to wind and tearing, with thickness measured in grams per square metre. The best breathable roof membranes and non-breathable membrane will always be those that strike a balance between thickness and affordability. 

At the same time as this, designers must always take into account the roofing system as a whole. The BS5250 code of practice gives guidance for control of condensation on all different pitched roofing structures.

 

Breathable Membrane and Non-Breathable Membrane at Roofinglines

We have a wide variety of breathable membrane and non-breathable membrane in different lenghts, widths and gsm in stock for 1 working day delivery. Shop from some of the industry's leading brands, including Tyvek, Klober and Cromar, at the best prices online guaranteed by the Roofinglines price match promise. Here are six of our favourites.

APEX Silver Breather Membrane 1m x 50m - 120gsm

 APEX Silver Breather Membrane 1m x 50m - 120gsm

Highly affordable underlay to protect against rain, dust and pollution

 

Cromar Vent 3 Classic Breathable Membrane - 1m x 50m - 115gsm

Cromar Vent 3 Classic Breathable Membrane - 1m x 50m - 115gsm 

Economical membrane suitable for supported and unsuported roof systems

 

DuPont Tyvek Supro Breathable Membrane - 1m x 50m - 145gsm

DuPont Tyvek Supro Breathable Membrane - 1m x 50m - 145gsm 

Extremely water resistant, air permeable underlay from market leader Tyvek 

 

Cromar Protect 1F Non-Breathable Membrane - 1m x 45m

Cromar Protect 1F Non-Breathable Membrane - 1m x 45m

Cheaper and easier to fit alternative to traditional bitumen based 1F felts

 

Klober Permo Extreme RS SK² Underlay - 1.5m x 50m

Klober Permo Extreme RS SK² Underlay - 1.5m x 50m 

Tear-resistant non-breathable underlay with high temperture stability

 

Klober Wallint 50 Vapour Control Layer - 1.5m x 50m

Klober Wallint 50 Vapour Control Layer - 1.5m x 50m 

 Provides an air barrier and vapour control on the warm side of the insulation

 

Shop Breathable Roof Membrane Shop Non-Breathable Membrane