An Airtight Case for Passive House Construction

Airtight construction is better for your home, your health, and the environment

The benefits of airtight construction methods are diverse. Projects suffer significantly less damage due to water vapor inside the walls. You can stop avoiding certain areas of your home because of bone-chilling drafts. It stops pollutants – and much of the noise – from filtering in from the outside.

Airtight construction is integral to the success of Passive House architecture, a green design that is so energy efficient it takes very little power to heat or cool a home. And its standards – while rigorous – are easier to attain than one might think.

To be designated as a Passive House, a building must meet a standard of best practices from the Passive House Institute that seal it from outside temperatures while maintaining high air quality and a perfect indoor environment. Its unique blend of airtight construction and high insulation is so energy efficient that proponents say heating and cooling can be run on the same amount of power it takes to operate two hand-held hair dryers. That’s about 90 percent less energy usage than traditional homes. 

Passive Houses are popping up nationwide as consumers demand ways to reduce their energy footprint and cut soaring energy costs. To date, these projects total more than 1.1 million square feet in the United States, with about 150 structures currently in use, reports the Passive House Institute US.

Without being airtight, Passive Houses cannot achieve the energy efficiency that defines them, as air leaks make heating and cooling systems work harder to maintain a consistent temperature. Leaks also reduce the efficiency of Passive House’s mechanical ventilation systems that remove stale air from the inside and replace it with a flow of fresh outside air.

As an added benefit, airtightness prevents the normal levels of moisture and humidity inside a home from being carried into the building envelope by unintended air leaks – a top cause of mold and other moisture damage.

An introduction to airtight construction

Put simply, airtight construction means no drafts. It does not permit any unintended gaps in the building envelope that enable air to leak in or out.

Selecting an architectural firm with Passive House training is critical to this process: airtightness requires a solid strategy at the design stage that clearly defines the location of the air barrier, what materials and components comprise it, and how junctions and penetrations are resolved. Poor design and detailing can lead to unintended gaps that cause junctions to not be constructed well or properly sealed.

For Passive House design to achieve its goals, a clearly identified air barrier or airtightness line must be created that it is continuous and joined up to form a loop. That doesn’t mean you can’t open doors or windows – rather, your architect needs to ensure the air barrier can pass the red pencil test: meaning that someone could trace the whole building envelope with a red pencil without any breaks.

Passive Houses are encased in ultra-thick insulation adjacent to the air barrier that completes the airtight shell. Stringent standards also revolve around doors and windows, which tend to be the culprits for cold drafts and room-to-room temperature variations in a building. High-performance choices, thoughtful placement, and impeccable installation with impeccable seals are critical to achieving airtightness.

Exacting procedures such as blower door testing must be performed to ensure that buildings exhibit the industry-leading leakage control necessary for Passive House certification. Special fog machines and infrared cameras are often used during construction to find the tiniest air leaks. Wall seams are treated with special tapes, gaskets, and sealants to ensure they don’t fail over time and cause drafts.

The materials required for airtight construction

There is no single material that must be used for airtight construction – the right choice is the one that integrates best with the type of construction system that’s selected. Some common materials used to form air barriers include wet plaster on masonry construction, reinforced concrete, Oriented Standard Boards of suitable thickness, and specifically designed airtight membranes. Certain “breathable,” or vapor permeable, materials can also be used in the building envelope. Insulation materials, which do improve energy efficiency, are generally not airtight.

But aren’t there going to be some necessary penetrations?

Yes, a few Passive House penetrations may have to occur from such items as electric cables, pipelines, and external wall power sockets. However, they must be carefully planned so that airtightness issues are resolved. The principle of avoidance should be applied first. And if penetrations are absolutely necessary, it’s better to concentrate them in as few places as possible.

Airtight construction does not pose a ventilation problem

Airtight or not, every building needs a ventilation system that channels fresh, clean air to the people inside. Passive Houses rely on energy recovery (ERV) or heat recovery (HRV) ventilating systems, a green mechanical technology that enhances air quality inside a home by acting like lungs to exchange stale indoor air for fresh air from the outside. This constant flow of fresh air makes these buildings both healthier and more comfortable.

Airtight construction protects Passive Houses from moisture damage, ensures draft-free comfort for the people inside, and is a critical component of the energy efficiency that defines this architecture.

At Aman Architecture, we’re generating architectural solutions that are functional, beautiful, and sustainable. For more information on our services, call 212-736-0480 or email at info@aman-arch.com

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