How can a building be both breathable and airtight?

Understanding the Vital Difference Between Breathable and Airtight 

This topic comes up frequently in the construction industry and can get confusing, especially if this is your first time building a home.

Embarking on a new building project can be both exhilarating and daunting. Among the many decisions you’ll face, understanding the difference between breathable and airtight construction is crucial in creating a comfortable home. Don’t worry if these terms seem unfamiliar— we’re here to break them down so you can make informed choices for your project.

Breathable, in this scenario, refers to the movement of moisture through building materials. Much like a Gore-Tex Jacket, breathable construction aims to allow moisture out whilst protecting against the wind and rain. If moisture gets into a building fabric and cannot escape or dry out, it can cause structural decay and create unhealthy internal environments, and is exaggerated in poorly ventilated buildings – much like using a bin-liner as a raincoat! 

Using breathable, or vapour-open, materials in construction aims to create a balanced environment within the building, allowing moisture to escape naturally while preventing excessive build-up.

Key features of breathable construction include:

Ventilation: Design elements such as windows, vents, and porous materials facilitate the exchange of indoor and outdoor air, promoting fresh air circulation.

Vapour-Open Materials: Materials like lime plaster, breathable membranes, and natural materials allow moisture to evaporate through the building fabric, maintaining optimal humidity levels.

Healthy Indoor Environment: Breathable construction reduces the risk of interstitial condensation or unwanted water in the structure, improving indoor air quality and creating a healthier and more comfortable living environment.

Following in parallel to breathability, airtight construction aims to control the air leakage through the building envelope – making sure our Gore-Tex jacket has no rips or tears and is the correct fit. Even if a building is designed with a high-performance, breathable system, every time this layer is broken, such as staples to secure a membrane or run cabling or pipework, this can allow moisture to travel in an uncontrolled and unexpected way.

In fact, the largest culprit for unwanted moisture movement in a building is due to gaps and cracks in the airtightness layer – up to 95% of all unwanted vapour! Improving airtightness ensures that the structural and insulative elements of the building can work as designed – regardless of the breathability design of the project.

This approach aims to enhance energy efficiency by preventing heat loss or gain, thus reducing the need for excessive heating or cooling systems.

Key features of airtight construction include:

Positive Design Concept: From the design of the building through to completion, all key members of the project should aim for the ‘build tight, ventilate right’ philosophy — minimising holes in the building and ‘designing in’ an airtightness layer.

Air Sealing Techniques: Dedicated systems and products, such as AeroBarrier, are employed to minimise gaps and cracks in the building envelope, thereby reducing air infiltration. 

Energy Efficiency: By minimising air leakage, airtight construction helps maintain consistent indoor temperatures, reducing the demand for heating and cooling energy and ultimately lowering utility costs. 

Comfort and Thermal Performance: Airtight buildings offer improved thermal comfort by eliminating drafts and cold spots, enhancing the overall liveability of the space.

Breathable and airtight construction aim for the same end result – making your home a more comfortable and healthier place to live. 

Breathable construction methods allow unwanted moisture to leave your home’s solid structure, and airtight construction systems prevent moisture from entering the structure in the first place! By combining the two, you’ll create a home that’s not only comfortable and inviting but also sustainable and cost-effective in the long run.

So, as you start on your self-build project, remember that breathable and airtight construction go hand in hand. With a little knowledge and planning, you’ll be well on your way to creating the home of your dreams – one that’s healthy, comfortable, and built to last.