Breathable roofing membrane underlay Vent3 PRO is a heavyweight, high performance underlay for cold and warm roof application. It has a weight of 165gsm. This is the highest rated breathable roofing membrane underlay in our range with a BS5534:2014 Wind Uplift rating of zones 1-4 with a 345mm lap fixing batten, and zones 1-5 with the addition of our Vent3 Double sided breather tape. With a 250mm or 100mm Lap fixing batten Vent3 Pro will reach zones 1-5. All our Vent3 Range of Breathable roofing Membrane underlays are BBA certified, you can download the certificates below. The main test the BBA do are highlighted below:
Resistance to Water Vapour:
This test checks how quickly a breathable roofing membrane underlay allows moisture-laden air to escape your roof. To qualify as a low resistance (LR) membrane. The lower the figure the better.
Moisture (water) Vapour Permeability:
The measure of how much moisture passes outwards through the breathable membrane in 24 hours. A higher value is better.
The breathable felt must be able to channel water into your gutters. To achieve this, the top layer of the fabric must be watertight. The BBA certificate tests for water tightness by measuring how high ahead of water can be contained, the higher the result, the less likely the fabric is to allow water through. To ensure ‘real-life’ results, both aged and un-aged samples are tested.
Tensile Strength / Nail Tear Strength
A breathable roofing membrane underlay must be strong enough to resist tearing. In addition to lasting the lifetime of the roof, a breather membrane has to be tough. This is so that it can withstand the installation and build process.
BBA certification tests the normal tear strength of the fabric.
A second test is performed to test how strong the fabric is after it has been punctured by a nail. The better it performs in these tests, the more likely it is to last longer. Tear strength is particularly important to professional roofers who need to lay large volumes of breathable roofing membranes quickly and without any hassle.
UV / Temperature Stability:
A breathable roof membrane/vapour permeable underlay is designed to be installed on your roof many days or even weeks before the final covering of slates or tiles. However, a vapour-permeable underlay will deteriorate with sustained exposure to the effects of UV light and temperature.
Wind blowing over and through your roof-space creates areas of high and low pressure. With an unprotected roof, slates and tiles are at risk from blowing out from the roof at the point where these low and high-pressure differences are greatest. A heavier breather membrane is more likely to restrict wind better and is less likely to split. You do not want to reduce airflow completely.