BREATHER MEMBRANE

Breather membrane is a screen layer designed to provide a barrier against water penetration from the outside while allowing migration of water vapour through the membrane from inside the building. Membranes can be installed either on a wall or pitched roof. This fantastic overlay is water resistant but vapour permeable, which means no water can get through the thickness of the membrane. Installed under roof tiles or against the inside face of an external wall, a breathable membrane is used to halt water ingress. At the same time, tiny pores in the material which are too small for water molecules to pass through, allow the passage of escaping water vapour, as it naturally travels towards the cold side. The membrane also has good air barrier characteristics designed to improve the air-tightness of the building. Installed over the roof structure they protect insulation from air and water infiltration and enable water vapour to be evacuated. This material is located on the cold side of insulation, beneath the tiles to terminate insulation and rafters from being exposed to humid conditions, debris and dust. Some types of products such as Novia Roof-Reflex AluThermo are combined with an insulation layer although its thermal conductivity can be as low as 0.0366 W/mK. If you are wondering which way round you should install breather membrane there is only one general rule to follow: with most brands of membrane such as Novia, Dupont Tyvek, Kingspan Nilvent, Kemper, Klober, Watco, Cromar, Delta and Bailey the printed side will be facing outwards. Roof membranes thicknesses are often referred to as the GSM symbol, which simply stands for 'Grams Per Square Meter'. The higher the value is often an indication of the thicker material. It is available in a variety of thicknesses such as 50GSM, 100GSM, 115GSM, 120GSM and 140GSM. Higher GSM roofing membranes are used where harsher wind conditions occur. Breather membrane is also measured in Resistance to Water Vapour. The 120GSM (heavy duty) & 140GSM (extra heavy duty) are far more durable geotextiles than the alternative 50GSM landscape fabric, making this type of membrane ideal for footpaths, driveways, and other high traffic areas. This is a measure of how quickly a breathable membrane allows moisture to escape. A low-resistant membrane will have a vapour resistance of 0.25MNs/g or less. The lower the number, the quicker the waterproof breathable membrane lets water vapour disperse. The higher the value, the better for this one, which measures how much moisture leaves through the waterproof breathable membrane every 24 hours. Breathable roofing membranes can last a lifetime, depending on the product and manufacturer guidelines. Each manufacturer should state the amount of overlap required between each length of the breather membrane. If you do need to replace your roofing membrane, it can cost anywhere between £638 per standard 115GSM black roll. Breathable roofing membrane is typically priced by square meter, with rolls available in standard 50 meter lengths. At 1 meter wide, this equals 50 square meters of membrane. Some manufacturers also provide a second width of 1.5 meters, which gives a total of 75 meters squared. Breathable roofing felt prices vary widely depending on their properties, and might range from as little as £1.25 per square meter (Novia Black 115GSM Roof and Wall) right up to £10.55 per square meter for more specialist products (Novia Roof-Reflex AluThermo Insulated Breather Membrane). UK customers use the terms ‘breather membrane’ and ‘vapour control layer or VCL’ interchangeably, particularly with regards to pitched roofs. Whilst they have a similar purpose, there are a couple of important differences between the two.

TYPES OF BREATHER MEMBRANE

There are a number of different types of breather membrane available, depending on the requirements of the project being undertaken.

VAPOUR PERMEABLE 
Vapour permeable breather membranes allow water vapour to pass through the membrane and out from walls and roofs. Vapour permeable breather membranes minimise the amount of water vapour that condenses within the roof or wall space, helping to minimise damp, mould and rot.

AIR PERMEABLE
Air permeable breather membranes have been designed specifically to allow both air and water vapour to pass through the roof or wall of a building. Using an air permeable breather membrane removes the need for a vapour control level, because vapour and air can freely pass through the membrane, and the air permeable membrane also provides a form of ventilation. Although air permeable membranes allow air and water vapour to pass through, they still act as a barrier to prevent rain, wind and snow from entering the roof or wall space.

TIMBER FRAME PERMEABLE
Timber frame permeable breather membranes are slightly thinner and lighter than a more traditional breather membrane. They have been manufactured for use on buildings with timber frames, and particularly during the construction process – timber frame breathable membranes can be used as temporary cladding to protect the structure from external weather conditions during construction, and then protect from internal moisture build up during and after building work has been completed.

LIQUID BREATHER MEMBRANES

In some cases, the structure of a wall or roof is quite complex, meaning fitting a breathable membrane is a challenge. In this case, a liquid breather membrane is the perfect solution - it can be applied with a paintbrush or roller, ensuring it covers the whole surface, including tight corners.

BREATHER MEMBRANE INSTALLATION

In order for the breather membrane to effectively protect the insulation from wetting it is important that it is continuous across the surface. Installing a roof breather membrane is a relatively straightforward process, but some steps must be adhered to in order to create a surface that is breathable and secure. To ensure maximum efficiency, all joints in the membrane should be properly sealed with tape so as to prevent accidental air-leakage. Firstly, it is important to have an eaves support tray or a UV resistant membrane, that is fitted along the eaves, with the bottom edge extending into the gutter. Next, lay the breather membrane parallel with the roof eaves. Make sure the bottom of the membrane is overlapping the eaves support tray or UV resistant membrane by at least 150mm, but not by so much that it will still be exposed when the roof tiles are laid. The breathable roof membrane should drape slightly between the timber rafters or counter battens, meaning there is a dip of around 10-15mm. Once you’ve checked that this is the case, add temporary clout nails to the top of the membrane – try to ensure they are above the line at which the second length of the membrane will overlap. When the tiles or slates are fitted they will provide a more secure fixing. Continue laying the lengths of breather membrane, working up the roof.