How To Use Breathable Membranes

How To Use Breathable Membranes
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How To Use Breathable Membranes

If you are constructing a new build with timber framework or renovating an existing building, breathable membranes are a great way to keep the building insulated and dry, while also giving the building’s frame an extra layer of protection.


Insulation Express have fantastic options from the highest quality and most well-known brands on the market, such as  Dupont Tyvek Housewrap Breather Membrane which is ideal for installing in homes.


What is a Breathable Membrane?


A breathable membrane is a sheet of material that is added to the outer side of insulation on roofs and walls of various buildings. Its main task is to allow any water vapour to pass through from the inside of the building without the need for any ventilation to be installed above the existing insulation layer.


It doesn’t just stop water vapour going from inside to out though, as it also prevents any moisture, surface water or rainwater from entering the building from outside to in.


How Does a Breathable Membrane Work?


As breathable membranes are water resistant, they are used when wall or roof structures aren’t fully water and moisture resistant. The membrane will be added on the cold side of the insulation, stopping any moisture from getting through and affecting the building. They are also air-permeable which allows the building to be ventilated properly, and thus preventing condensation building up.


Breathable membranes can act as an added layer to help prevent harsh environmental factors like rain and dirt from making their way in and causing damage.


Why do you need to fix a Breathable Membrane?


Adding a breathable roof membrane is extremely important when maintaining a healthy structure to your building. As they assist with the safe passage of water vapour from outside to in as well as inside to out, they help to prevent the build-up of condensation. This means that mould, damp, and rot don’t cause issues in your building.


With the installation of breathable membranes, moisture is allowed to exit the roof area, while also providing protection from any rainwater making its way in, thus keeping the roof area dry.


What happens if you don’t have a Breathable Roof Membrane?


If you opt to go without a breathable roof membrane, you’re taking a massive risk that moisture will pass through the material on the external side of the roof. The effects of this would be that there’s a build-up of moisture and water on the layer of insulation, both making it ineffective in doing its job and causing further issues like damp and rot.


Rain on Rooftop


How to Install a Roof Breathable Membrane


If you have decided to install a roof breathable membrane to your building, simply follow these steps.


  1. Eaves Support Tray


Before getting started, make sure you have an eaves support tray or a UV resistant membrane that’s fitted along the eaves. The bottom edge should be extending into the gutter.


  1. Lay Down the Breathable Membrane


The next step is to actually lay the membrane itself, which should be parallel with the roof eaves. The printed side of the membrane should be facing outwards when it’s installed, with the bottom of the membrane overlapping the eaves support tray or UV resistant membrane by a minimum of 150mm.


You’ll need to make sure the overlap is not so much that the membrane will be exposed when the roof tiles are laid down, as this will cause issues for you.


  1. Drape the Membrane


The breathable roof membrane will need to drape a little bit between the rafters or battens, with a dip of around 10 to 15mm. After making sure that the dip is there, you can add nails to the top of the membrane, ensuring that they are above the line where the second length of the membrane will overlap. When the tiles are added, it will mean a secure fixing.


  1. Lay the Remainder of the Breathable Membrane


You’ll then need to lay down the remainder of the membrane, working your way up the roof. How much overlap you need will depend on the brand that you are using, and they should state the required amount as necessary.


If you need to install an extra timber batten to make sure the overlap remains and to stop the tiles from touching the membrane, then you can do so. The drape of the underlay needs to remain as it allows water to pass down the surface of the membrane as required.


If you are installing to a commercial or residential building, then Dupont Tyvek Supro Breather Membrane will be the ideal product for you. 


What Else Needs to be Considered?


There are some other things to consider in different scenarios when installing breathable membranes.


Roof Valleys


With any roof valleys, you’ll need to make sure that the breather membrane is extended by at least 300mm on each side, measured from the middle of the valley. With any abutments, the underlay will need to be turned up by a minimum of 100mm, creating a secondary water-resistant section.

Roof Verges


If it’s a wet verge, the membrane will need to lap onto the masonry by a minimum of 50mm. If it’s a dry fix verge, the membrane will need to be installed so that it extends past the face of the gable.


Ridge Ventilation


If there is ridge ventilation in the roof, you’ll need to cut the breather membrane on each side of the ridge to make sure that the path of ventilation remains clear. Without ridge ventilation, the membrane will need to go over the ridge, overlapping each side of the ridgeline.


Following these tips when insulating your roof can help you ensure that no mistakes are made, as well as reviewing our blog section for extra tips on how to install roof and loft insulation effectively.