How to install breathable roof membrane

Here at Roofing Superstore we have a number of breathable roof membranes available for your latest roofing project, from Tyvek Supro breather membrane, to Cromar’s breathable membrane, TLX breathable pitched roofing felt, Klober Permo and more.

If you have any queries or project-specific questions, feel free to call our team on 01752 692760 or use the live chat in the bottom right hand corner and they will be more than happy to help.


Why do you need a breathable roof membrane?

Breathable roof membranes are crucial in pitched roofing projects, as they prevent the build up of condensation, which can lead to damp, mould and rot. They allow moisture to move out of the roof space, whilst still preventing rainwater ingress, ensuring that the roof space stays dry.

Without a breather membrane, moisture will pass through the external roof material, then build up on the insulation layer, making the insulation ineffective, or even build up within the roof space, causing damp, mould and rot.


How to install a roof breather membrane

Installing a roof breather membrane is relatively straight forward process, but there are some steps that must be adhered to in order to create a surface that is breathable and secure.

Eaves support tray

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.

Lay the breather membrane

Next, lay the breather membrane parallel with the roof eaves – normally, when installing breather membrane the printed side should face outwards. 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.

Ensure draping occurs

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 membrane will overlap. When the tiles or slates are fitted they will provide a more secure fixing.

Lay the rest of the breather membrane

Continue laying the lengths of breather membrane, working up the roof. Each manufacturer should 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 to ensure the overlap remains, and to prevent the tiles from touching the membrane. These can be added across the top of the underlay, but the drape of the underlay must still exist to allow the rainwater to pass down the surface of the membrane.


Other considerations

Ridge ventilation

If the roof includes ridge ventilation, the breather membrane must be cut on each side of the ridge to ensure the path of ventilation is still clear. If there is no ridge ventilation, the breather membrane should go over the ridge, and overlap each side of the ridge line by the required overlap.

Roof valleys

On roof valleys, ensure the breather membrane is extended by a minimum of 300mm on each side, measured from the centre of the valley. At abutments, the underlay should be turned up by at least 100mm – this will create a secondary water resistant barrier.

Roof verges

With wet verges, also known as verges that use mortar bedding as fixings, the breather roof membrane needs to lap onto the masonry by at least 50mm. When used with dry fix verges, the membrane needs to be laid so that it extends past the face of the gable.

Penetrations

For windows, soil pipes and other penetrations, cut the membrane and turn it so that it folds up against the penetration. If working with circular 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.


Unsure of the best breather membrane for your project? Don’t hesitate to give our team a call on 01752 692760 or use the live chat and they will be more than happy to offer product recommendations and advice.

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