How Airtightness Drives Energy, Comfort, and Durability in Buildings

In modern construction, performance is no longer optional.

Energy codes are tightening.
Clients expect lower operating costs.
Mechanical systems are being engineered with greater precision.
And building science is exposing where traditional assemblies fall short.

At the center of all of this is one critical variable:

Airtightness.

Not as a buzzword.
Not as a checklist item.
But as a measurable indicator of whether a building truly performs as designed.

Airtightness directly influences:

• Energy consumption (and long term utility costs)
• HVAC load accuracy
• Interior comfort
• Moisture management
• Long-term durability

But here’s the deeper truth:

Airtightness doesn’t just affect performance — it reveals whether a building is a coordinated system or a collection of layered parts.

And in today’s construction environment — where labor variability, compressed schedules, and performance verification are the norm — how airtightness is achieved matters just as much as the final ACH number.

For architects and builders pursuing high-performance results, airtightness is not a detail to patch at the end. It is a design decision made at the beginning. 

Before Diving Into Airtightness, It Helps To Understand How Building Envelopes Perform as Systems  ⇒ Why the Best Building Envelopes Are Designed to Work Together as a System

What Is Airtightness — And Why It Matters

Airtightness refers to how well a building’s enclosure resists uncontrolled air leakage between the interior and exterior.

In simple terms:

• A tight building controls where air enters and exits.
• A leaky building allows unintended air movement through seams, gaps, and penetrations.

This uncontrolled air movement affects:

• Energy performance (and utility costs)
• HVAC load assumptions
• Interior comfort
• Moisture transport within assemblies
• Long-term durability

It’s important to clarify:

• Insulation slows heat transfer.
• Airtightness controls air movement.

You can have high R-values and still have a leaky enclosure.

A truly high-performance building requires both thermal resistance and air barrier continuity.

How Is Airtightness Measured?

Airtightness is verified through a blower door test.

During testing:

• A calibrated fan is installed in an exterior doorway.
• The building is depressurized (or pressurized) to 50 Pascals.
• The airflow required to maintain that pressure is measured.

The result is expressed as:

ACH50 — Air Changes per Hour at 50 Pascals

This number indicates how many times the total volume of air inside the building is replaced in one hour under test pressure.

Did You Know:  Real-world SIP projects routinely test below 2 ACH50, and many high-performance SIP buildings achieve airtightness results in the 0.5–1.0 ACH50 range when properly detailed and installed. That level of performance is consistent with high-performance building programs and Passive House benchmarks (≤0.6 ACH50).

How to Interpret ACH50

• Lower ACH50 = tighter building
• Higher ACH50 = more uncontrolled air leakage

Typical ranges:

• Conventional new construction: 3–7 ACH50
• Code minimum (varies by region): often ≤ 3 ACH50
• High-performance construction: 1.0–2.0 ACH50
• Passive House standard: ≤ 0.6 ACH50

For architects and engineers, ACH50 directly impacts:

• Energy modeling inputs
• Infiltration assumptions
• Mechanical system sizing
• Ventilation strategy

For builders, blower door testing is where performance claims are verified.

Airtightness is no longer theoretical — it is measurable and documented.

Targeting a Specific ACH50 for Your Project?

If your project has a performance target — whether code-minimum or high-performance — our team can review your enclosure approach and discuss realistic pathways to achieve it.

Connect With a SIP Specialist

Airtightness: System-Level Strategy, Not a Late Add-On

Airtightness should be designed in — not added on after the fact.

Too often, airtightness becomes a late-stage correction:

• Extra taping after drywall
• Spray foam touch-ups before final inspection
• Emergency sealing ahead of (or after!) blower door testing

When airtightness is treated as a field fix, it becomes reactive rather than intentional.

High-performance buildings take a different approach. They treat airtightness as a system-level enclosure strategy defined during schematic design and coordinated across:

• Structural layout
• Mechanical design
• Penetration planning
• Envelope detailing

When airtightness is embedded into the structural system itself, it reduces:

• Trade overlap at air barrier locations
• Redundant materials
• Transition complexity
• Field variability

The result is not just a better test number. It is a more predictable outcome.  Airtightness is not something to “patch.”
It is something to engineer.

Why Airtightness Matters in Modern Construction

Airtightness influences far more than a single test result.

It directly affects:

• Heating and cooling energy use
• HVAC equipment sizing accuracy
• Interior comfort stability
• Moisture control within assemblies
• Long-term structural durability

Three major forces have elevated airtightness from “best practice” to essential design strategy:

1. Energy Codes Require Verification

Modern energy codes increasingly require verified air barrier performance through blower door testing. Design assumptions must now withstand field measurement.

2. High-Performance Standards Demand Precision

Programs such as LEED, Net-Zero Certified & Passive House require extremely low infiltration rates, leaving little room for execution variability.

3. Owners Expect Predictable Outcomes

Both commercial and residential owners expect things that an airtight envelope delivers, including:

• Reduced operating costs
• Stable indoor comfort
• Durable assemblies
• Fewer callbacks

Airtightness is the bridge between modeling and lived performance.

But how airtightness is achieved matters just as much as the final number.

Did You Know?
SIP-built structures have been shown in DOE and ORNL testing to be up to 15× more airtight than traditional stick framing with batt insulation, significantly reducing uncontrolled air leakage and supporting tighter thermal control.

Why Airtightness Is Difficult to Achieve in the Field

In conventional construction, airtightness is largely dependent on jobsite coordination. Air control is spread across multiple layers, installed at different times, and handled by different trades. Framing, sheathing, weather barriers, insulation, and interior finishes are often completed in separate phases, sometimes weeks apart. Each handoff introduces risk.

Every transition between materials creates an opportunity for continuity to break down. Individually, these gaps may seem minor. Collectively, they can undermine airtightness across the entire building envelope. Common risk areas include:

• Rim joists
• Top plates
• Window rough openings
• Electrical boxes
• HVAC & Plumbing penetrations
• Roof-to-wall transitions

When airtightness depends heavily on field execution, variability increases — and that variability shows up during blower door testing.

Late-stage air sealing fixes can add cost and schedule pressure. The growing reliance on interior-applied air sealing systems reflects this reality. These solutions are often used to compensate for air leakage that originates from fragmented envelope assemblies rather than poor materials.

When airtightness must be corrected late in the construction process, it’s usually a sign that air control was treated as a layer to be added, not a system designed from the start.

For builders, that introduces uncertainty.
For architects, that introduces performance deviation.

Airtightness Challenges Often Start With How Walls Are Framed. Explore How Conventional Assemblies Introduce Hidden Complexity ⇒ The Hidden Cost of Studs

Two Primary Approaches to Achieving Airtightness

Understanding the strategic difference between layered and integrated systems is essential. Most projects pursue airtightness using one of two approaches. Both can work, but they differ significantly in how airtightness is achieved and maintained.

1. Layered Air Barrier Assemblies

This method builds airtightness by combining multiple materials in the field. (Stick framing + taped sheathing such as ZIP System + insulation)

Products such as the Huber ZIP System are designed to function as both structural sheathing and a weather-resistive barrier, with taped seams forming the air barrier when installed correctly. Taped sheathing systems like ZIP represent an improvement over traditional house wrap because the air barrier is integrated at the sheathing plane and seams are mechanically sealed. These ZIP System have been shown to reduce air leakage by roughly 25–40% compared to traditional taped house wrap and untreated OSB, provided seams and penetrations are meticulously detailed in the field.

Advantages:

• Familiar workflows
• Flexibility across assemblies

Limitations:

• Precise field installation (performance dependent on execution)
• Multiple trades required
• Weather during installation 
• Surface preparation
• Consistent detailing at hundreds of seams
• Roof & wall assemblies are typically different
• Tape adhesion quality
• Field detailing at penetrations
• Greater variability in ACH results

Airtightness becomes a coordination challenge.

2. System-Based Airtightness (Integrated Enclosure Strategy)

Structural insulated panels are a panelized construction system that integrate structure, insulation, and sheathing into one engineered assembly. Manufactured offsite, in a controlled factory environment, panels arrive to job sites pre-cut to exact floor plans, 

Advantages:

• Large-format panels (up to 8' x 24' in size) reduce seam frequency
• Structural sheathing and insulation is integrated
• Panels can be used for floors, walls and roof
• Continuous insulation across the assembly reduces thermal bridging (key energy code requirement)
• Air sealing is concentrated at panel joints
• Factory-controlled, precise, manufacturing improves consistency
• Simplified trade coordination (SIPs are installed with one crew)

This reduces:

• Trade overlap (fewer transitions reduce risk)
• Redundant air barrier layers
• Transition complexity
• Field variability

Instead of assembling performance layer by layer on site, airtightness becomes inherent to the system.

For builders and architects focused on predictable performance and reduced risk, that distinction matters.

Disadvantages:

• Upfront planning requirements 
• Less field flexibility after fabrication 
• Perceived material cost (this myth ignores many factors, dive into that here) 
• Engineering & Structural Spanning Considerations (SIPs require thinking in panels, not sticks.

Airtightness Comparison: Layered vs Integrated System Assemblies

How airtight are SIP buildings compared to ZIP System walls?

Both system-based and layered assemblies can achieve strong airtightness when properly executed.

However, real-world blower door results show that:

• SIP projects frequently test below 2 ACH50
• High-performance SIP buildings often fall in the 0.5–1.0 ACH50 range
• Layered taped-sheathing assemblies can perform well but show wider variability depending on field execution

The comparison below outlines where these approaches differ in predictability, coordination, and long-term risk exposure.

This is not about preference.

It is about predictability and risk management.

High-performance teams do not just pursue airtight buildings.
They pursue repeatable airtight results.

Note: systems-based airtight design does not remove the need for skilled labor. It supports it. Installers spend less time compensating for misalignment or correcting gaps and more time executing a clear, coordinated plan.

Evaluating SIPs vs Framed Wall Assemblies?

See how SIP wall systems are detailed and installed — including panel joints, transitions, and connection details.

⇒ View SIP Wall & Roof Details

How Airtight Are SIP Buildings Compared to the ZIP System?

Architects and builders frequently ask:

“How do SIP assemblies compare to ZIP System walls in terms of airtightness?”

The ZIP System combines structural sheathing with a factory-applied WRB layer and relies on taped seams to establish air and water control.

When properly installed and taped, ZIP System assemblies can achieve good airtightness results.

However, airtightness in ZIP-based assemblies depends on:

• Field taping quality
• Seam continuity across every panel joint
• Penetration sealing
• Transition detailing at rim joists, top plates, and openings
• Coordination between trades

In other words, performance is highly dependent on field execution.

By contrast, SIP assemblies:

• Reduce seam frequency through large-format panels
• Integrate structural sheathing on both sides
• Consolidate air sealing primarily at panel joints
• Eliminate redundant cavity framing that increases transition complexity

This does not mean ZIP assemblies cannot perform well.

It means that the path to airtightness differs:

• ZIP System: layered field-assembled air barrier strategy
• SIP System: integrated enclosure strategy

For teams pursuing high-performance targets — particularly below 2.0 ACH50 — reducing seams and transition points becomes increasingly important.

Airtightness becomes easier to achieve when there are simply fewer opportunities for discontinuity.

Airtight Envelopes Help Reduce Energy Demand For The Life Of The Building

⇒ Explore The Unmatched Energy Efficiency of SIPs

How Airtightness Affects HVAC Sizing and Energy Modeling

Infiltration is a major input in energy modeling.

When air leakage is reduced:

• Heating and cooling loads stabilize
• Equipment sizing becomes more precise
• Mechanical systems operate closer to design intent
• Energy modeling aligns with as-built performance

Excess infiltration forces conservative mechanical sizing to compensate for uncertainty.

This often leads to:

• Oversized systems
• Reduced efficiency
• Humidity control challenges

A stable enclosure enables mechanical systems to operate as designed.

Designing for Verified Performance?

If airtightness, HVAC optimization, or high-performance certification is part of your project goals, start the enclosure conversation early.

⇒ Schedule a Design-Phase Consultation

Comfort: Where Performance Becomes Noticeable

Airtightness directly impacts occupant comfort.

Reduced uncontrolled air movement results in:

• Fewer drafts
• More stable interior temperatures
• Improved humidity control
• Reduced cold wall effects

Comfort consistency is often the most noticeable benefit of a high-performance enclosure.

Airtightness and Moisture Control: Protecting Durability

Air carries moisture.

When uncontrolled air moves through wall and roof assemblies, moisture follows.

Over time, this can lead to:

• Condensation
• Mold growth risk
• Material degradation
• Reduced assembly lifespan

A well-designed airtight enclosure reduces moisture transport at its primary pathway — uncontrolled airflow.

Durability begins with air management.

Designing for Predictable Performance

If your project goals include:

• Verified energy performance
• HVAC optimization
• High-performance certification pathways
• Reduced callback risk
• Long-term durability

Airtightness strategy must be addressed during schematic design — not after framing.

The enclosure is not a collection of materials.

It is a system.

Explore Verified Studies That Show How SIPs Deliver Measurable, Long-Term Results
⇒ Proof in Performance Series

The Strategic Takeaway for Builders and Architects

Airtightness has earned its place in conversations about building performance, and it is a proven lever for energy efficiency, comfort, moisture control, and durability.  But it works best when it’s treated as a design strategy, addressed during schematic design — not a jobsite challenge after framing.  

Airtightness is not about choosing better tape.

It is about choosing an envelope strategy. The enclosure is not a collection of materials.  It is a system.

For teams prioritizing:

• Energy predictability
• Mechanical coordination
• Durability risk management
• High-performance certification

The difference between field-assembled airtightness and integrated airtightness becomes significant.

Layered, field-applied systems can perform well when executed meticulously. However, airtightness that relies on perfect execution at every step is inherently more vulnerable.

System-based assemblies reduce variability, risk and simplify performance outcomes.

Want to design higher-performing, airtight buildings with confidence?

• Explore SIP Wall & Roof Systems
• Browse High-Performance SIP Projects
• Request Project-Specific Pricing
• Connect With a Building Performance Specialist

Airtightness is measurable.

The strategy you choose determines the result you deliver.

Frequently Asked Questions

What is airtightness in construction?

It is the resistance of a building enclosure to uncontrolled air leakage.

Why is airtightness important in building design?

Airtightness controls unintended air movement, which affects energy use, moisture transport, comfort, and HVAC performance.

How is airtightness measured?

Through blower door testing, expressed as ACH50.

Is airtightness just about passing a blower door test?

No. Blower door tests measure results, but airtightness is created through envelope design and continuity.

What airtightness level should I target?

Targets vary by project goals, climate, and code, but designers often reference standards like Passive House (e.g., ≤ 0.6 ACH50) as high-performance benchmarks.

What ACH50 is considered high performance?

1.0–2.0 ACH50 is common for high-performance construction. Many advanced programs aim for ≤2 ACH50, with Passive House targeting ≤0.6 ACH50. Appropriate targets depend on climate zone and project goals.

How do SIPs achieve airtightness differently than traditional framing?

SIPs integrate structure, insulation, and air control into a single system, reducing seams and reliance on field-applied air barriers.

Is taped sheathing like ZIP effective for airtightness?

Yes. Taped sheathing systems can significantly improve airtightness compared to untaped sheathing and house wrap when properly installed. Performance depends heavily on detailing and field execution.

Do SIPs eliminate the need for air sealing?

No. Proper detailing at panel joints and penetrations is still required. However, the number of required field seams is typically reduced compared to layered assemblies.

Does airtightness mean no ventilation?

No. Airtight buildings require controlled ventilation to ensure air quality and remove pollutants without losing thermal performance.

Do SIP buildings still require ventilation?

Yes. Airtight envelopes require intentional, controlled ventilation to maintain indoor air quality.

Can airtightness reduce HVAC system size/costs?

Yes. Predictable airtightness reduces heating and cooling loads, allowing HVAC systems to be sized more accurately, improving efficiency and reducing equipment costs.

How does airtightness affect moisture control?

Air leakage carries moisture into assemblies. Reducing uncontrolled air movement helps limit condensation and durability issues.