It’s one of the most crucial yet often overlooked aspects of home construction. It’s misunderstood, and sometimes even completely dismissed. It’s airtightness! And today we’re here to explore the basics of what you need to know.

If you're curious about building a healthy, comfortable, and energy-efficient home, understanding airtightness is essential. Let's dive into why it's such a vital feature of high-performance and passive house designs and construction.

What is airtightness?

Airtightness refers to a home's ability to control air movement between the inside and outside. Think of it as creating a continuous, sealed envelope around your living space. This envelope prevents uncontrolled air leakage, which can significantly impact your home's performance and comfort.

To measure airtightness, professionals use a metric called Air Changes per Hour at 50 Pascals (ACH50). It’s tested by simulating windy conditions to see how much air escapes from your home (more on testing later). The lower the number, the better the airtightness.

But here's the thing: most homes are like sieves, with air sneaking in and out through all sorts of nooks and crannies. Just check out the diagram below.

Why is airtightness a core feature of high-performing homes?

Airtightness isn't a buzzword; it's a fundamental principle of modern, efficient home design and construction.

Passive House, one of the most rigorous energy-efficient building standards, requires exceptional airtightness – typically 0.6 ACH50 or less. While it may not be realistic to achieve this level of airtightness for every home and budget, it demonstrates the importance of this principle in high-performance building design.

Here's why it's so important:

1. Energy efficiency: An airtight home requires less energy to heat and cool, leading to lower utility bills and therefore a reduced carbon footprint.

2. Comfort: By eliminating drafts and maintaining consistent temperatures, airtight homes provide superior comfort year-round.

3. Durability: Controlling air movement also means controlling moisture movement, which can significantly extend the life of your home's structure and materials.

The benefits of airtightness

Let's break down the advantages of an airtight home in more detail:

Improved energy efficiency

An airtight home prevents unintended air exchange with the outside, allowing your heating and cooling systems to maintain the desired temperature efficiently without constantly fighting against air leaks. These air leaks can cause 15-25% of winter heat loss in buildings (CSIRO).

Enhanced comfort

Say goodbye to those mysterious drafts and cold spots. Because airtight homes maintain more consistent temperatures throughout, you’re also living in a more comfortable environment.

Better indoor air quality

Controlled ventilation (which we'll also touch on later) goes hand in hand with an airtight home. Combined, you get to predominantly breathe in the fresh, filtered air you’re controlling, reducing dust, pollen, and other pollutants (creating a healthier home).

Moisture control

By preventing warm, moist air from entering wall cavities and other vulnerable areas, airtightness significantly reduces the risk of mould growth and structural damage.

Soundproofing

An unexpected bonus of airtightness is improved sound insulation. Those sealed gaps don't just block air; they also help keep outside noise where it belongs – outside.

The role of airtightness in insulation efficacy

You could have the best insulation money can buy, but if your home isn't airtight, that insulation won't perform to its full potential. That’s because of something called “wind washing”.

Wind washing occurs when air moves through or around insulation, reducing its effectiveness. It's like wearing a warm jumper on a windy day without a windbreaker – the wind cuts right through, negating much of the sweater's insulating properties.

An airtight building envelope protects your insulation from wind washing, ensuring it can do its job effectively. This means your insulation performs as intended, maximising your home's energy efficiency.

Achieving airtightness in homes

Creating an airtight home requires attention to detail during both the design and construction phases. Here are some key considerations:

• Continuous air barrier: Ensure there's a continuous air barrier around the entire building envelope.

• Sealing penetrations: Pay special attention to areas where pipes, wires, or vents penetrate the building envelope.

• Quality windows and doors: Use high-quality, well-sealed windows and doors to minimise air leakage.

• Professional installation: Proper installation techniques are crucial for achieving airtightness.

Balancing airtightness with ventilation

You might be wondering, "If my home is airtight, how does fresh air get in?" It's a common misconception that homes need to "breathe" through random air leaks. In reality, what we want is controlled ventilation, not haphazard air leakage.

Modern, airtight homes use mechanical ventilation systems, typically Heat Recovery Ventilators (HRVs) or Energy Recovery Ventilators (ERVs). These systems bring in fresh air while recovering heat (or coolness) from the outgoing air, ensuring good air quality without sacrificing energy efficiency.

Testing for airtightness

The most common method for testing airtightness is the blower door test. This involves using a powerful fan to depressurise the house and measure how quickly air enters through leaks. It's a valuable tool for identifying areas that need improvement and verifying the overall airtightness of a home.

Source: energy.gov (left); yourhome.gov.au (right)

Without getting too technical, the lower the Air Changes per Hour (ACH) number, the better.

• A typical Australian home might have 10-30+ ACH

• A high-performance home is <3 ACH and a passive house sits at 0.6 ACH or less

That last number might seem extreme when compared to the standard homes most of us are living in, but the results speak for themselves in terms of comfort, energy efficiency, and overall home health.

Wrapping it up

Airtightness isn’t just about energy savings – though that's definitely a significant benefit! It's about creating homes that are more comfortable, healthier, and more durable for you and your family, for decades to come.

Understanding airtightness is a crucial step in making informed decisions about your home's design and construction. Whether you're building new or renovating, considering airtightness can lead to a home that not only performs better but also provides a superior living experience.

Hi, we’re Amity Builders

We’re a passionate bunch who are tired of seeing homeowners around Australia settle for subpar living conditions. We combine our love for building, building science, and building relationships to create healthy, comfortable, and energy efficient living experiences for people. We’d love to get to know you!