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How Do You Install A Breather Membrane

By John Doe
Published in Domestic Roof
March 08, 2021
5 min read
How Do You Install A Breather Membrane

What Is A Breather Membrane ?

What is a breather membrane ? One definition is that it is a transluscent plastic sheet designed to be installed as the outer layer of roof insulation.

Another definition talk about breathable membranes being multi-layered sheets which allows vapour transmission, and still another refers to them as moisture vapour permeable under-roof sheets. Of course, different breathable membranes each have their own properties.a breather membrane is an essential part of a batts & blown insulation roofing assembly, due to the nature of the tongue and groove assembly used for roofing. The tongue and groove arrangement means that there will be plenty of air spaces between each batten.

Drawings on this page show how a breather membrane works with batts and blown insulation.not all membranes are made the same. Our breathable roofing systems are manufactured to en-13727, europe’s highest specification.

Making it tougher than anything else on the market – which means that your property will be protected now and in the future.are you wondering what a breather membrane is? You’ve probably heard the term used before, but never knew what it really was. Or whether you needed one and where exactly to put it on your roof.the national federation of roofing contractors (nfrc) definition of a breather membrane is an installed sheet of polyethylene or polypropylene that allows air leakage in .

Starting At The Eaves

About 12 months ago, we were replacing the roofing of a house in rural queensland and during the quotation process we noticed that on one side of this house we had not found any membrane at all.

Upon further investigations we found that  there was no support tray at the eaves. All that we could see was the felt backing soaked in brown water: there’s nothing more unattractive than wet rain gutters and back-up over-hangs, and the potential for mold build-up is real.it’s a common practice in the roofing industry to support the membrane on flashings or copper ‘u’ chases.

One of the most popular areas we are seeing this in at the moment is at the initial eaves.

Simple products such as felt trays are being used which not only support the membrane, but also protect it from water ingress…a major advantage of felt support trays is that they are completely glued the underside of the gutter limiting the exposure to uv and it’s long term effect on degradation. Felt support trays are prone to heat damage if large overhangs occur, so always check eaves details with the builder.

Drape The Underlay

With some help from a fellow colleague here are some alternative ways to provide the best possible waterproofing protection for your building. Waterproof membrane is used in most situations to ensure no moisture is allowed to leak through the roof space. For this purpose, a vapor permeable membrane such as vaproshield® ought to be used.

However it could be tempting to use a non-permeable membrane which would potentially save you money and time. This is not advisable as moisture will get trapped within your building, leading to problems down the track and water ingress through the roof voids.underlay (water resistant barrier)– the underlay (also known as water resistant barrier, wrb) will prevent a flood when it rains and stops water penetrating the membrane. The term underlay is used within the uk and australia but elsewhere its known as breather. Underlays can be manufactured from felt, self-adhesive membrane or more rigid plastic materials with a variety of coatings to help it last longer.

You will also have insulating underlays (for loft floors etc) which aren’t really suitable for a roof covering but they too fall into this category.once you have laid the membrane, you need to drape it properly. The purpose of the draping process is to keep as much moisture away from the membrane as possible. This is achieved by keeping moisture from running off the membrane with some gentle dips or creases. Take your time, we would rather you took an hour so it looks great instead of rushing and looking at it again in a year!.

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.

Verge Detail

The best way to block rainwater and cold air from getting under the edge of the roof is with a verge. To install this, lay membrane behind it. Verge fascia are easily available for diyers, we will be using a plastic version, normally found in garden centers.

It’s used on raised dry stone borders and works by allowing water to drain through without penetrating and protecting the gap so that air can’t get in. Fill gaps between the membrane and house walls with cavity sealer as you’d do with battens.cover the verge between two and five centimetres (1-2 inches) depending on your chosen technique. One option is to fix the membrane so it sits on top of the verge, another option is to use a “dry” verge (see below).

Either way, use a paintbrush or similar tool to apply an even layer of selleys membrane adhesive for verges over the membrane.a verge is the board that runs along the ridge of a roof. A dry fix verge is one that is attached on both sides to the apex of the roof with galvanised nails or screws. The membrane is then attached to the timber and cement rendered on the face of the gable using blue tape.set the membrane against the face of the gable and mark where the membrane will be trimmed to form a butt joint with the existing verge. Remove the membrane, make your cuts and replace it.

Roof Penetrations

Sealing off voids is a very commonly-performed task, and this one’s really simple! If your roof has penetrations, simply slide the membrane over it, fold it up against the penetration, then fold back down again - securing it in place. You might need some tape to hold the cut-out sections into place if they don’t stay on their own.

If you have a date stapled to the membrane (instead of a label with adhesive), seal it in place with tape too.for penetration barriers, use building paper or ‘uv block’. You can order uv block from most paint stores. To install, cut the membrane to size with a sharp knife (this is easier and safer than trying to tear it) so that it overlaps the penetration by 10–15mm on all sides.

Lay the membrane down over the rood, then nail it into place with your hammer and roofing nails or staples.for small openings, use a painter’s masking tape to tape across the opening and weather-strip needles or roofing nails with the heads cut off (to avoid puncturing the membrane) to create a seal. Large openings should be covered with housewrap (self-adhesive plastic sheeting) cut to size and attached to the flashing.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.by applying a membrane dam for roof penetrations, you create an “armor” around the penetration in case of a leak. This is especially important if you use penetrations for ventilation.


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John Doe

John Doe

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