Can a breather membrane be used as a roof covering??

Ⅰ，What is a breather membrane ?

Breather membranes are sheet or liquid applied materials that contain many very small holes or pores. Vapour permeable breather membranes protect against wind, insects, dirt, weather penetration whilst insulating your property.
Installed to the outer side of the insulation, over or under the counter-battens on a pitched roof, breather membranes allow water vapour to escape from inside a building.
Often without the need for ventilation.

Structure diagram of Breather membrane

Ⅱ,Quick Details of the breather membrane

1) Type:Waterproof Membrane
2) Width:150cm
3) Length:50cm
4) Water vapour Transmission:3000gr/m2/24hrs
5) Application:roofing application wall application
6) Thickness:0.25mm 0.35mm 0.45mm 0.49mm
7) Weight:80g 100g 120g 140g 160g

Ⅲ,What is their function?
The function of breather membranes is to provide a barrier against water penetration from the outside while allowing migration of water vapour through the membrane from inside the building.
While being typically associated with rainscreens, their use is not always well understood and they are not always required.

Where to use breather membranes?
Breather membranes are installed on wall or roofs. They are used on external or cold sides of the wall insulation, under the outside surface of the external lining or roof tile or even cladding.

Install on wall :

Install on roof :

Ⅳ, Why do we need the breather membrane ?
Building Regulations demand ever higher thermal efficiency.
Today’s building envelopes are becoming increasingly airtight.
Whilst beneficial for the energy performance of our homes, airtightness makes careful consideration and management of moisture more critical than ever.
Studies have shown that ventilating directly above an insulation layer can reduce its thermal efficiency.
Which means more and more people are opting for an un-ventilated roof. This is where breather membranes come in!
They also protect against condensation that can cause mold and structural damage from rotting timbers when a roof is not able to dry out sufficiently.

Ⅴ,How to  instal breather membrane
Check before you begin:

Check the ventilation requirements of the membrane will be met.
Close the top of the brickwork cavities.
Ensure the insulation is correctly installed at the wall plate to avoid a thermal bridge.

Starting at the eaves
The UV resistant membrane along the eaves is a crucial detail.
Traditionally the bottom edge of the membrane is extended either half-way or 150mm into the gutter. However,  long term exposure of the roofing underlay at the eaves, leads to degradation.
A simple and effective solution is a felt support tray. 
These direct the water from the underlay prevent felt from sagging at eaves level providing a clear drainage point into gutter.

Drape the underlay
When your membrane is taught the moisture will not run off as fast.
This increases the risk of ingress. Draping, ensuring it dips between the rafters or counter batten, provides channels to allow the rainwater to pass down the surface of the membrane. 
We suggest a dip of approximately 10-15mm. Check that this is the case, adding temporary clout nails to the top of the membrane.
Try to ensure they are above the line at which the second length of membrane will overlap.  The final covering of tiles or slates will provide a secure fixing.

Manufacturer's instructions state the amount of overlap required between each length of breather membrane.
If the overlap does not coincide with a timber batten an additional batten can be installed. This ensures the overlap remains, whilst preventing the tiles from touching the membrane.
They are added across the top of the underlay.

Ridge detail & ventilation
At the ridge the felt needs to overlap approximately 150mm over the top of the ridge.
The felt from the second side of the roof needs to overlap the top of the felt from the first side and nailed through the top of the rafters on the first side.

For all new build homes, ridge or high-level ventilation must be installed when a vapour permeable membrane is installed. Other warm or cold pitch roof structures do not require additional roof space ventilation.
However, we recommend being thorough and prudent when you are installing. Manufacturers rigorously test their membranes they’re able to support sole ventilation,
but  ridge or high-level ventilation for tight fitting tiles and slates will help moisture vapour to disperse more easily when air temperatures are very low.
For roofs requiring ridge ventilation, cut the breather membrane as per manufacturer’s instructions on either side of the ridge to ensuring the ventilation airways are clear.

Roof penetrations
Around chimneys, soil pipes, etc. cut the membrane and turn it so that it folds up against the penetration.
For round penetrations, cut the membrane with an Asterix shape to create flaps to fold upwards.
If needed, tape the cut-out sections to the penetration to prevent them from folding back down.

Ⅵ,Recommendations
If a breather membrane is required, there is a need to consider factors such as:

Sealing around penetrations.
Can the material used act as an air barrier, or is a separate air barrier required?
How the slab edge deflections are accommodated.
How the membrane will be secured to resist cyclic wind loading.
How the membrane will be secured around steel edge beams.

Ⅶ,DERFLEX is a professional Super Clear PVC Film Transparent PVC Tarpaulin Manufacturers & Suppliers from China for 16years.

Shanghai DER New Material Co., Ltd is professional manufacturer of PVC coated tarpaulin, experience over 18 years.
2 knife coating production line, 4 calenders, 8 lamination machine, we make both laminated and coated PVC tarpaulin material for various applications.
As an PVC material experienced company, DER has expanded the marketing to all over the world by attending different kinds of exhibitions, like IFAI, SGIA, Techtextil and China Sign and so on.
Now we have many customers from UK, Russia europe countries, North America countries, like United States, Canada, South America, like Mexico, Agentina, Span, Africa, such as South Africa, Kenya, Nigeria, Tanzania and other countries in the world.

 If you have more interest, please contact us freely, Email :Masha@derflex.com , WhatsApp: +86 131 6285 8753