Airtightness FAQs

Your go-to guide to Passive Purple airtightness

Getting up to speed on the vapour control membrane lingo and what it means for your building’s airtightness and energy consumption can be a little tricky. To help you get up to speed, we’ve put together this comprehensive FAQ guide so you can find all you need to know about how these products work, what they do and what their features actually mean for your build.

What is airtightness?

Airtightness is ultimately the goal of all vapour control membranes. These products help achieve airtightness to maximise the energy efficiency of a building. We want to do that because it’s good for the planet, and the residents can save significantly on electricity costs. 

Airtightness is one of the key elements of a Passivhaus building. Traditionally, if there was an air leak, we would introduce heating or cooling systems to compensate, but this is wildly energy inefficient, not to mention it costs a fortune.

According to Passivhaus airtightness standards, there should be no more than 0.06 air changes per hour (ach). To achieve this, you will need an airtightness membrane that seals connections, blocks air leaks, and adds insulation.

Coating the inside of the building with an airtight membrane makes it airtight — no vapour can penetrate. The result is indoor climate control without costly heating and cooling systems.

What is a liquid applied airtight membrane?

Liquid applied membranes are the most efficient solutions to cover the necessary surfaces at a quick pace while ensuring that airtightness of 0.06ach or less is achieved.

Liquid applied vapour control membranes can be applied with a spray gun, ramping up efficiency, requiring just one operator to cover a significant surface in a short amount of time.

Passive Purple‘s liquid applied membrane sprays onto surfaces to form a tough but flexible polymer membrane. This ability to move with the building settlement and stay strong against impacts damage makes it a superior solution against classic paper membranes, which quickly crack, peel, tear, and wear.

Is liquid applied airtight membrane the same as liquid applied vapour control membrane?

Yes. Although the terms can change between liquid-applied vapour control membrane and airtight membrane, the meaning is the same. The goal of a vapour control is to control vapour (moisture) through the building fabric which also seals leaks in the construction of a building, therefore Vapour control and airtightness are efforts toward the same goal.

Is a liquid applied airtight membrane the same as a liquid applied vapour control membrane?

What are the benefits of using liquid-applied membranes?

The primary reason why builders try to achieve airtightness is to maximise the energy efficiency of the building. Airtightness helps to keep the temperature you want inside, minimising heating requirements, working with nature and the bodies in the house to keep it cosy.

Airtightness ensures that there are no air leaks that let cool air in or warm air out — or vice versa in the opposite seasons. The benefit of achieving airtightness with a liquid-applied membrane is that it drastically speeds up the process. The fiddly work that would have been required with traditional methods is eliminated, and just a single operator of a spray gun can cover an area of 300m2 in a single day.

Where should liquid airtightness membrane be applied?

Liquid applied vapour control membranes should be applied to all of the areas on the warm side of the insulation — the external envelope — including connection areas to the roof, wall, floor and joist. It’s worth paying extra attention to wall and ceiling connections to ensure they are airtight and be mindful when two different materials connect — such as concrete and red brick or steel — as these can have different reactions in humidity.

How long does the spray application take?

Passive Purple’s liquid applied airtight membrane, used with a spray device, requires just one installer to apply up to 300m2 of the liquid applied airtight membrane in a single day.

How long does the spray application take?

What needs to be prepared before applying an airtight membrane?

While applying an airtight membrane is very simple, there are a few housekeeping steps to check before pulling out the roller or the spray gun. Any materials and surfaces to be coated need to be dust-free, solid and closed. This means closing any holes and joints. Those below 2-5mm can simply be closed with Passive Purple Liquid Brush, but anything above will need to be closed with a cement-based product or polyurethane foam.

Can liquid applied membranes be used without a spray gun?

Yes. Liquid applied airtightness membranes can be applied to surfaces with a roller if you don’t have access to a spray gun. Of course, this takes longer than applying the membrane by spray device, but it goes on just as well.

What's the difference between brush applied airtightness and a liquid-applied airtight membrane?

The role of both products is to achieve airtightness, but they are designed a little differently. We’ve already covered liquid-applied vapour in quite a bit of detail, so here we will look at brush on airtightness.

Brush on airtightness is made with fibre reinforced polymer technology. It is thicker than the spray-on membrane, making it perfect for filling gaps (no more than 10mm). Beyond filling gaps, the brush applied airtightness is designed to seal over joints and gaps to reduce air leakage.

It’s worth considering the brush on airtightness as an extra airtightness defence to prepare your building before spraying the larger surface.

What is Passive Purple?

Passive Purple is an Intelligent Membrane product that comes in liquid-applied and brush-applied forms. As Passivhaus builders ourselves, we set out to develop better technologies to achieve Passivhaus airtightness standards. Liquid applied and brush applied airtightness technologies are a far more efficient means than the old school paper membranes that we had to deal with in the past.

Passive Purple is today the leading Passivhaus airtightness product.

Passive Purple airtight membrane

Is Passive Purple Passivhaus certified?

Yes. All Passive Purple products are Passivhaus certified. To achieve this certification, airtightness products have to be 0.06 air changes per hour (ach) or lower. Passive Purple is 20x lower than this requirement, with a Passivhaus score of 0.03ach.

In addition to Passivhaus certifications, Passive Purple is BBA certified and certified as a radon barrier. It is also an M1 class, VOC-free water-based product, meaning that it is completely chemical-free and environmentally friendly.

Can liquid applied membranes be used without a spray gun?

Yes. Liquid applied airtightness membranes can be applied to surfaces with a roller if you don’t have access to a spray gun. Of course, this takes longer than applying the membrane by spray device, but it goes on just as well.

why CHOOSE Intelligent Membranes?

Intelligent Membranes live and breathe membranes and airtightness. We are committed to the ongoing development of Passive Purple and other technologies to improve the environmental impacts that can be affected through Passivhaus buildings.

Passive Purple and the team at Intelligent Membranes have your building covered with the best airtightness membrane on the market.

Visit the Passive Purple family of products.

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