Building Airtightness & Control Layers – The Risinger Build Ep. 12

Foreword by Ian Thompson, Editor

Today, on The Risinger Build, we’re tackling one of the most overlooked yet essential elements of high-performance home building — airtightness.

It’s perhaps the most controversial building science subject at the moment because many building consent departments, designers. and builders don’t really understand why we would want to build an airtight home. But importantly, if we are going to design and build an airtight home then we must enable air movement, because its essential to move air in, around, and out of the house. Make any sense?

It’s all about maintaining good air quality, and we’ve published many video posts on this subject already, but for now, let’s see how Matt builds a good airtight home.

The Risinger Build: Episode 12 – Airtightness & Control Layers

Building Airtightness: Video Summary

Understanding the Importance of Airtightness in Home Building: Key Takeaways from the Risinger Build Series

Welcome back to the Risinger Build series! In this episode, we’re diving deep into the nitty-gritty of home construction, focusing specifically on airtightness and how to properly seal penetrations in a house. Airtightness is a critical aspect of building a high-performing, energy-efficient, and healthy home. Let’s break down the key educational points from this episode.

The Concept of Airtightness

To start, it’s essential to understand why airtightness matters. Imagine driving down the highway with a car window that’s slightly open and won’t close all the way. It’s noisy, inefficient, and uncomfortable. Similarly, a house with leaks and gaps allows unwanted air infiltration, leading to energy loss, discomfort, and even pest problems.

Contrary to the common myth that “houses need to breathe,” the truth is that we want our homes to be as airtight as possible. By sealing the house properly, we gain control over the indoor environment. This control allows us to manage ventilation on our terms, ensuring that the air entering the home is fresh, filtered, and conditioned appropriately.

Building a Tight Envelope from the Start

A significant part of achieving airtightness starts with the framing stage. In this project, the team framed the walls so that the roof connects directly to the wall sheathing. This method eliminates the common issue of rafters poking through the walls, which can create gaps and leaks.

By ensuring that the trusses and rafters are clipped and stop at the wall sheathing, we’re able to create a smooth transition from the wall to the roof. This design allows us to tape and seal that joint effectively, forming a continuous air barrier. It’s about thoughtful framing that sets the foundation for airtightness.

Sealing the Foundation to Framing Connection

Another critical area for air sealing is where the framing meets the concrete slab. The team used a bead of Lexel sealant underneath and on top of the sill sealer before placing the bottom plate. This method creates a tight seal between the concrete and the framing, which is often a notorious area for air leaks.

To reinforce this connection, a “belt and suspenders” approach was applied. After the initial sealing during framing, the team went back to apply a fluid-applied membrane from Prosoco called Joint & Seam Filler (the pink product). This application provides an extra layer of protection, ensuring that even if there’s movement or slight gaps, the seal remains intact.

The One Thing for One Hole Mantra

A crucial principle emphasized in the episode is the mantra “one thing for one hole.” This concept means that for every hole drilled in the building envelope, only one item (like a wire, pipe, or duct) should penetrate. By adhering to this practice, we minimize the size of openings and make them much easier to seal effectively.

For example, in the garage wall shared with the kitchen, each wire has its own hole drilled through the wall sheathing. This approach allows for precise sealing around each penetration using fluid-applied products like Prosoco’s Fast Flash or Huber’s Liquid Flash. It significantly reduces the potential for air leaks at these critical points.

Using Fluid-Applied Membranes for Sealing

Fluid-applied membranes play a significant role in achieving airtightness in this project. The team utilized several products from Prosoco’s line, each designated by color for specific applications:

Post-Trades Blower Door Test: After the trades completed their installations, another test was conducted. Despite some minor unsealed holes, the house maintained a tight envelope with a score around 0.69 to 0.70 ACH50.

These tests are invaluable tools for identifying areas needing attention before it’s too late. Waiting until the end of the project to test can make it challenging to address issues effectively.

Pink (Joint & Seam Filler): Contains fibers for bridging gaps and is used at joints and transitions, such as between the foundation and framing.

Red (Fast Flash): A smooth, fiber-free product used for sealing around windows, doors, and penetrations. It comes in gun grade (thicker) and roller grade (thinner) viscosities.

Gray (Zip System Liquid Flash): Similar to Fast Flash, used interchangeably depending on the application.

These products are compatible with the Zip System sheathing used on the house, providing a continuous and durable air barrier when applied correctly.

Addressing Penetrations Throughout the Building

Every penetration in the building envelope was carefully sealed. Whether it’s for HVAC lines, electrical wires, or plumbing vents, the team made sure that each had its own sealed opening. For instance:

HVAC Penetrations: The line sets and control wires for HVAC units were individually sealed using fluid-applied membranes. This method prevents air leakage and ensures energy efficiency.

Electrical and Plumbing Penetrations: Similar care was taken with electrical outlets, exterior lights, and plumbing vents. Each penetration was sealed from both the outside and inside.

The Benefits Beyond Airtightness

Sealing the building envelope doesn’t just improve energy efficiency; it also enhances indoor air quality and comfort. By preventing uncontrolled air infiltration, we reduce the likelihood of condensation within wall cavities, which can lead to mold growth and structural issues.

Moreover, a tightly sealed house is less prone to pest invasions. In regions like Texas, where bugs and pests are a significant concern, airtightness serves as a first line of defense against unwanted critters entering the home.

Testing and Verification

To ensure that the sealing efforts were effective, the team conducted blower door tests at multiple stages:

Pre-Trades Blower Door Test: Before the mechanical, electrical, and plumbing trades began their work, the house was tested and achieved a commendable score of 0.38 ACH50 (Air Changes per Hour at 50 Pascals). This score indicates a highly airtight building envelope.

Key Details Inside the Home

Inside the house, the “one thing for one hole” principle continued to be applied. The team made sure to seal all penetrations from the inside as well, using products like Prosoco’s AirDam, specifically designed for sealing the interior side of windows and doors.

Moreover, the team highlighted the potential issues with fireplaces. Traditional fireplaces can be significant sources of air leakage. In this project, the decision was made to eliminate the indoor fireplace and instead focus on an outdoor unit. This choice not only improves the airtightness of the home but also enhances indoor air quality.

Embracing Continuous Improvement

An important takeaway from the episode is the commitment to continuous improvement. By learning and applying best practices, like the ones shared by building professionals such as Jake Bruton and Steve Baczek, builders can progressively improve the performance of each home they build.

Whether it’s adopting new sealing techniques, using advanced materials, or rethinking traditional design elements like fireplaces, every step contributes to building better, more efficient, and healthier homes.

Conclusion

Achieving airtightness in home construction is more than just a trend; it’s a fundamental aspect of building science that leads to energy efficiency, improved indoor air quality, and overall homeowner satisfaction. By focusing on thoughtful design, meticulous sealing of penetrations, and utilizing advanced materials and methods, builders can construct homes that stand the test of time.

In this episode of the Risinger Build series, we’ve learned the importance of starting with airtight framing, the value of the “one thing for one hole” practice, and the effectiveness of fluid-applied membranes in sealing the building envelope. We’ve also seen the benefits of testing and verification through blower door tests.

By embracing these principles and striving for continuous improvement, builders can achieve impressive airtightness levels, even surpassing stringent standards like those of Passive House. It’s about taking pride in the work, aiming for excellence, and ultimately delivering homes that are comfortable, efficient, and built to last.

Final Thoughts

If you’re a builder aiming to improve your craft, consider adopting these practices into your workflow. Test your houses during construction, pay attention to the details, and don’t be afraid to rethink traditional methods that may hinder performance. And remember, achieving an ACH50 below 1.0 is an outstanding accomplishment, placing you in the top echelons of home builders.

Special thanks to the partners who made this project possible, including Builders FirstSource for their digital tools and Prosoco for their high-quality sealing products. By working together and sharing knowledge, we can all contribute to building better homes for the future.

Related

Are We Designing Airtight Houses Properly?

Using Blower Door Tests (with Smoke) to Qualify Airtight Home Building Performance

A Net Zero House Project Using an Off-Site Manufactured House. Was It Worth It?

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