Energy Efficiency and Building Science News

Insulation Is Great Energy Efficiency Tax Policy

Tue, 2019-08-27 11:41
Building ScienceEnergy Efficiency

The United States has long had tax incentives encouraging domestic energy production, for everything from oil and gas to nuclear and wind power. We do this for many reasons: to ensure stable supplies of home-grown power, to make energy more affordable, and to incentivize cleaner, greener options.

It all makes sense, except that we’ve left behind the single best solution we have for meeting these goals: energy efficiency. As swaths of the country face unrelenting heat waves, we currently have no federal tax incentives encouraging consumers and businesses to use their energy more wisely, such as through buying a more efficient air conditioner or installing insulation in a home.

This is an egregious hole in federal policy. For all the talk of a Green New Deal or a Green Real Deal, fixing this gap in the tax code is one thing Congress could pass tomorrow, with bipartisan support, to significantly reduce carbon emissions while simultaneously stimulating economic activity.

Efficiency is an engine of economic growth and increased productivity. It is by far the largest job creator in the clean energy economy, supporting more than 2.3 million jobs nationwide — good-paying jobs such as retrofitting buildings or manufacturing high-efficiency components and equipment. And it saves consumers and businesses money, freeing up billions of dollars that can be invested elsewhere.

Any politicians who say they are looking for climate change solutions that protect American economic growth and competitiveness need to look no further than energy efficiency. Yet Congress is hardly giving these incentives the time of day.

Specifically, Congress allowed three key efficiency incentives for homes and buildings to expire at the end of 2017. One of these gives homeowners a tax credit for improving the efficiency of their home or buying high-efficiency equipment.

Another encourages home builders to build tighter, more efficient new homes. And a third encourages efficiency improvements in commercial buildings.

Homes and buildings alone account for 40 percent of U.S. energy consumption and nearly as large a share of carbon emissions. Many of them will be in use for 50 or 100 years, so by failing to encourage efficiency now, we are effectively locking in wasted energy and unnecessary carbon emissions for decades.

In addition to preventing waste, updated incentives would create tens of thousands of jobs. History has shown that home and building owners will change their behavior with meaningful incentives. They’ll install insulation or more efficient windows. They’ll buy a new high-efficiency air conditioner or water heater.

That not only stimulates manufacturing at factories across the United States, but it puts contractors and construction crews to work in residential and commercial buildings. In fact, 6 in 10 of the nearly 2.3 million energy efficiency jobs in the United States work in construction.

But these incentives must be modernized and reinstated. The expired incentives were largely written 15 years ago. What was an energy-efficient air conditioner or furnace then isn’t today, and we need to modernize the incentives to better reflect today’s technology and markets.

The benefits to consumers, businesses and the planet would be significant. A Department of Energy analysis published in 2018 looking at just five product categories under the expired homeowner incentive (central air conditioners, gas and electric water heaters, gas furnaces, and electric heat pumps) found that increasing the incentives and extending them for 10 years would increase sales by 278 percent. That would translate to $52 billion in energy savings — equivalent to eliminating the electricity use of nearly half of all U.S. households for a year.

The direct impact on both energy efficiency, lower energy costs and improved economic activity is why the incentives have broad support from the environmental community as well as manufacturers, contractors, engineers and architects. It’s also why this should be an easy win for Congress.

For additional information, read the following articles:


Presentation: What Is the Value of Continuous Insulation?

Tue, 2019-08-27 11:16
Building ScienceEnergy Efficiency

Continuous insulation is used on foundations, exterior walls, and roofs. In addition, continuous insulation provides maximum thermal performance by minimizing thermal bridging. It provides optimal assemblies that dry and also minimize seasonal moisture variations, creating a stable and durable environment for the building structure and interior. Continuous insulation products can also provide products that serve multiple functions including thermal insulation, water-resistive barrier, and air barrier (some composites even add a wall-bracing function or roof ventilation function).

Jay Crandell, P.E., addresses these topics in his “Continuous Insulation: Research, Applications, and Resources for Walls, Roofs, and Foundations” presentation, originally given at the 2019 RCI International Convention and Trade Show.

While the options and opportunities continuous insulation presents are significant, the application must also accommodate cladding installation, fire performance requirements, and other matters important to overall constructability and code compliance.

Crandell’s presentation provides an excellent primer on the many applications of continuous insulation based on a comprehensive body of building science knowledge. This work has resulted in recent key building code and energy code advancements. Review the presentation and more and many more technical resources found at


How Do WRBs & Drying Concepts Work in Exterior Walls?

Wed, 2019-08-21 14:17
Building ScienceEnergy Efficiency

Illustration by Hunter Lane, Applied Building Technology Group

For a boat hull, it is best to essentially eliminate wetting potential with the use of a highly water- and vapor- resistive hull, or at least outer coating on the hull, right? In this case, drying potential is easily handled on the interior side by use of a small bilge pump or bailer.

Exterior walls of buildings are a bit trickier, but similar in principle. First and foremost, wetting potential from rain water must be minimized by proper use of a water-resistive barrier and best-practice flashing details at all windows, doors, and other penetrations.

Any reasonable approach to or amount of drying potential will not offset major water-resistance defects that result in excessive wetting potential from rain water intrusion. For example, if a boat has holes in the hull the approach of installing a larger bilge pump (aka, more drying potential) to remove the water may in some cases keep the boat afloat temporarily, but it is not going to make it seaworthy. Fix the holes. Similarly, trying to rely on high drying potential (rather than focusing on fixing the holes or water leaks) can lead to increased wetting potential from inward water-vapor movement for reasons given earlier. The three stooges make some fun of this point. Don’t be a stooge

Figure 1. The Drying Potential Balancing Act

For drying potential of a building’s walls, one must be careful to allow adequate vapor movement out of the assembly, but not in a way that allows a lot of vapor movement back into the assembly under changing seasonal conditions. This can be a challenging balancing act (see Figure 1) that depends on a number of factors, including the cladding material used, the climate zone where the building is located and the vapor permeance of building material and insulation layers making up the wall assembly. 

Consequently, a safe and simple design approach for building a sound wall assembly is to use a moderate- to low- vapor permeance material layer on the exterior of the wall and let the wall breathe to the interior by use of a moderate- to high- vapor permeance interior vapor retarder, such as a Class II (Kraft paper), Class III (latex paint) or a “smart” vapor retarder. This approach works well because the water-sensitive interior portions of a wall become influenced by a more stable indoor environment and are protected from the variable outdoor conditions that otherwise create episodes of wetting and drying. Also, the balance of wetting and drying potential with adequate inward drying minimizes moisture cycling of materials within the wall. This is good for the structure.  This is good for durability. This is good for water sensitive materials within walls such as wood-based or gypsum sheathings. This is simple, but it must be done right…

While the above inward-drying approach can work in any climate, in colder climates the wall must be “tricked” into thinking it is in a warm climate to control humidity levels with the assembly and prevent condensation or moisture accumulation within the wall during the winter months. This beneficial effect is easily and reliably achieved by using a sufficient amount of continuous insulation, like foam sheathing, on the exterior of the building as is often required to comply with modern energy codes. 

In fact, a wall calculator tool and educational aids have been developed for this purpose. Foam plastic insulations, like plastics commonly used for boat hulls, also have a comparatively high level of durability when exposed to water, which can be further enhanced by facers (like the gel coat on a boat hull). With these moisture control and durability benefits, energy savings are also obtained by envelope insulation of the entire exterior of a structure, including all the thermal bridges created by wood and, to a much greater extent, steel framing members.

Conversely, walls with no exterior continuous insulation result in cold materials within the wall (such as wood-based or gypsum sheathing) and this tends to create high humidity or condensation conditions that increase the moisture content of these materials during the winter, which can lead to moisture related and durability issues. Even with high exterior drying potential leading to drying in the Spring and Summer, the moisture cycling in the winter may lead to potential moisture damage unless a low-perm interior vapor barrier is used and careful air-sealing applied to prevent vapor diffusion and warm indoor air leakage into the wall. Also, in warm-humid climates, a high outward drying potential really means that during much of the year there is high inward wetting potential due to inward vapor diffusion. In this case, focusing instead on inward drying and avoiding high vapor permeance materials on the exterior is a favorable practice.    

So, don’t be fooled by narrowly focused claims that foam sheathing creates low drying potential without considering the fact it can significantly reduce and control wetting potential while, together with appropriate vapor retarder selections, also provide appropriately balanced and inwardly directed drying potential for a durable and energy efficient wall assembly suited for any climate.

For additional information, please review the following articles, as well as the previous videos in this series:

Water Resistant Barriers Topical Library on

Perfect Wall Articles

  1. Creating the ‘Perfect Wall’: Simplifying Water Vapor Retarder Requirements to Control Moisture
  2. Perfect Walls are Perfect, and Hybrid Walls Perfectly Good
  3. Wood Framed Wall Insulation Calculator Explained
  4. New Wall Design Calculator for Commercial Energy Code Compliance
  5. Energy Code Math Lesson: Why an R-25 Wall is Not Equal to a R-20+5ci
  6. Continuous Insulation Solves Energy Code Math Problem

Video Series

  1. Fear Building Envelopes No More with This Website & Videos
  2. Thermodynamics Simplified Heat Flows from Warm to Cold
  3. Moisture Flow Drives Water Induced Problems
  4. Video: How the 'Perfect Wall' Solves Environmental Diversity
  5. Video: How Important Is Your WRB?
  6. Video: A Reliably Perfect Wall Anywhere
  7. Video: The Best Wall We Know How to Make 
  8. Video: How to Insulate with Steel Studs
  9. Video: Thermal Bridging and Steel Studs
  10. Video: Better Residential Energy Performance with Continuous Insulation
  11. Video: How to (Not) Ruin a Perfectly Good Wall
  12. Video: Tar Paper and Continuous Insulation? No Problem!
  13. Video: Do CI and WRBs Go Together?
  14. Video: Assess Your 'Perfect Wall' Using Control Layers


How Exterior Walls Breathe

Wed, 2019-08-21 13:06
Building ScienceEnergy Efficiency

Illustration by Hunter Lane, Applied Building Technology Group

Unlike boats, a building’s walls must have some capability to “breathe” instead of being totally impervious to all forms of water. However, a misguided reliance on “breathing” or drying potential as the primary means to make a building’s wall work, without proper consideration of variations in conditions of use, can lead to the problem of wetting potential being too high when conditions of use change.

What you end up with is a wall that dries fast in one condition of use and then wets just as fast in another condition of use – just like the boat in the cartoon. Water or water vapor that leaves in one direction can also enter in the opposite direction when conditions change. For the boat illustration, the rate and direction of water movement depends on the size of the hole and the water pressure difference (which changes depending on whether the boat is in the water or dry-docked). Similarly, water vapor movement depends on the vapor permeability of material layers and the vapor pressure difference across those layers (which changes direction seasonally).

Because walls in buildings dry by means of water vapor movement, use of a high vapor permeance water-resistive barrier layer on the outside of the wall is often considered to be universally good.  In some circumstances this may be true and is helpful.  In many others, it is not. The problem is that vapor drives are not always in the outward direction.  In fact, they are often in an inward direction.  Furthermore, just focusing the vapor permeance of one layer does not fully address how the assembly will behave under changing circumstances.

The direction and amount of water vapor movement into or out of the wall depends on the time of year, the climate, the indoor conditions (temperature and relative humidity), the vapor permeance of the material layers that make up the wall assembly, and the type of cladding. In particular, moisture reservoir claddings like stucco or adhered masonry veneers can significantly increase inward vapor drives when not adequately back-ventilated.  So, having high drying potential on the exterior side of a wall assembly can be good at one time of the year in some climates and for some cladding types, but not for all times of the year in all climates for all cladding types.  This seems complicated and it is.

There are resources should you want to take a deep-dive into this subject.

The Applied Building Technology Group has created two calculators to help evaluate energy code thermal insulation compliance and building code water vapor control compliance.

It performs the following two design checks for a user inputted wall assembly:

  1. Computes the assembly U-factor (and effective R-value) and compares it to code minimum thermal performance requirements (maximum U-factors)  found in 2015 IECC Tables C402.1.4 and R402.1.4 (IRC Table N1102.1.4)  which are climate dependent. An R-value of 0.17 and 0.68 are assumed for exterior and interior air films, respectively.
  2. Conducts a water vapor control check as an aid to help determine if the proposed wall assembly also complies with minimum building code requirements associated with various interior vapor retarder options which are dependent on climate and other factors such as insulation amount and location or sheathing type/permeance and cladding ventilation.

For further information or assistance, please email us at

For additional information, review the following articles, as well as the previous videos in this series:

Perfect Wall Articles

  1. Creating the ‘Perfect Wall’: Simplifying Water Vapor Retarder Requirements to Control Moisture
  2. Perfect Walls are Perfect, and Hybrid Walls Perfectly Good
  3. Wood Framed Wall Insulation Calculator Explained
  4. New Wall Design Calculator for Commercial Energy Code Compliance
  5. Energy Code Math Lesson: Why an R-25 Wall is Not Equal to a R-20+5ci
  6. Continuous Insulation Solves Energy Code Math Problem

Video Series

  1. Fear Building Envelopes No More with This Website & Videos
  2. Thermodynamics Simplified Heat Flows from Warm to Cold
  3. Moisture Flow Drives Water Induced Problems
  4. Video: How the 'Perfect Wall' Solves Environmental Diversity
  5. Video: How Important Is Your WRB?
  6. Video: A Reliably Perfect Wall Anywhere
  7. Video: The Best Wall We Know How to Make 
  8. Video: How to Insulate with Steel Studs
  9. Video: Thermal Bridging and Steel Studs
  10. Video: Better Residential Energy Performance with Continuous Insulation
  11. Video: How to (Not) Ruin a Perfectly Good Wall
  12. Video: Tar Paper and Continuous Insulation? No Problem!
  13. Video: Do CI and WRBs Go Together?
  14. Video: Assess Your 'Perfect Wall' Using Control Layers


Installed Building Products Announces Acquisition of Therm-Con, LLC and Foamtech, Inc.

Wed, 2019-08-21 12:35

Installed Building Products, Inc., an industry-leading installer of insulation and complementary building products, announced the acquisition of Therm-Con, LLCand Foamtech, Inc. (collectively, “Therm-Con”). Founded in 2005, Therm-Con primarily serves the Tennessee market, as well as the Georgia and Alabama markets through a branch location in Chattanooga, Tennessee. The company provides insulation, fireplace, shower doors, closet shelving, and mirror installation services primarily for residential customers.

“With trailing twelve-month revenue of $4.7 million, Therm-Con enhances our presence in attractive markets throughout Tennessee and its surrounding states,” stated Jeff Edwards, Chairman and Chief Executive Officer. “To date, we have acquired over $30 million of annual revenues, which primarily consists of insulation installers. Acquisitions remain a key component of our growth plan and we continue to have a robust pipeline of acquisition opportunities across multiple geographies, products and end markets.”


Air-Sealing the Lid: Spray Foam and Cellulose Team Up for a High Performance Solution

Wed, 2019-08-21 12:18
Building ScienceEnergy Efficiency

I’m a second-generation home builder working in northeastern Connecticut, and I’ve been building net-zero energy homes for about 10 years. In my early years doing this, I experimented with structural insulated panels (SIPs) and other methods, but these days, I have settled down to a formula based on a cellulose-insulated double stud wall sheathed with plywood on the outside, and a flat attic with deep blown cellulose. I shoot for a HERS rating of about 40 without solar, and I get the rest of the way to a HERS zero rating by installing photovoltaics on the roof.

The author protects can lights in the attic using Tenmat mineral-wool hats.

The spray-foam contractor then seals the hats down to the attic floor with a flash coat of high-density closed-cell polyurethane foam.

In 2010, I was trained and certified as a Passive House consultant, although I’ve never actually built a certified Passive House. Because of client budgets and performance expectations, I typically take a step back from Passive House in terms of insulation levels and window performance. This allows me more freedom to use a variety of building forms and gives customers more choice around things like window placement.

At the same time, the spray-foam contractor seals the gaps at the outside edge of the ceiling.

Partitions also create potential air leaks, both where the ceiling drywall butts to the wall and through wiring penetrations. So this location also gets a flash coat of spray foam.

However, my company does routinely reach the Passive House metric for airtightness. We blower-door test all our houses for Energy Star certification, and they typically measure tighter than 0.6 ACH50—usually, somewhere between 0.3 and 0.5. One way we reach that level of airtightness is by focusing on the attic, including the critical juncture between the walls and the roof.

It starts with the double stud wall. As I mentioned, we sheathe the exterior walls with plywood. Then we cover the sheathing with Henry Blueskin to provide an airtight drainage plane. The outer stud wall and the inner stud wall are connected at the top with a continuous gusset of 3/4-inch plywood that is glued to the wall top plates. That stops any air leakage from outside those walls.

Click for enlargeTim Healey

But this still leaves a leak point where the ceiling drywall butts up against the edge of the plywood gusset joining the wall plates. We address that joint from above. The spray-foam insulation contractor goes up into the attic and applies a flash coat of foam to that joint between the drywall and the exterior walls. He does the same thing at all the interior partitions.

We also spray-foam any penetrations in the ceiling. Where we have can lights, we install Tenmat mineral-wool hats over the lights ( and then cover the hats with spray foam. With all the joints and penetrations sealed with foam, we can now proceed to insulate the attic using 20 inches of loose-fill cellulose.

When all the leak points have been sealed with spray foam, the author’s crew installs 20 inches of blown-in cellulose insulation to complete the insulated attic assembly.

This method is simple but effective. I just received the finalized HERS rating for a house we completed a few months ago, built with the same methods I’m showing here. The house had a HERS score of -14 (37 before PV). The blower-door test came in at 0.53 ACH50.

Photos by Ted Cushman

For additional information regarding air-sealing, read the following articles:


Water-Resistive Foam Board Insulation

Wed, 2019-08-21 09:54
Building ScienceEnergy Efficiency

Halo Exterra, a foam board insulation for above-grade exterior insulation applications is also designed to be a water-resistive barrier (which means that no building paper needs to be used).

How is this possible and what do installers have to say about it?

This blog post will show you exactly how Halo Exterra was constructed to be a water-resistive barrier and what builder Anthony Dew of Stalwood Homes thinks about it.

How Exterra is Constructed to be a Water-Resistive Barrier

There are two components that contribute to the water-resistive barrier capabilities of Exterra:

  • its foam core thickness; and
  • the use of laminates.

First and foremost, Exterra is made with a graphite polystyrene (GPS) foam core. GPS is a graphite-enhanced expanded polystyrene foam that provides superior R-value, and it’s this component that makes Exterra a unique foam board insulation product. For Exterra to act as a water-resistive barrier, its GPS foam core must be 9/16” or thicker.

Secondly, Exterra is also laminated on both sides with a polypropylene film (which adds durability and flexibility). The laminate layers of Exterra are precision-perforated, allowing air and moisture to escape and therefore resulting in another key benefit: its breathability. You can read more about the science here.

The key is to have breathable micro perforations and to still qualify as a water-resistive barrier, which is the unique balance that Halo Exterra achieves.

Exterra has also undergone rain penetration testing.

What’s the result of the unique design and construction of Halo Exterra?

The result is a foam board insulation product with a built-in water-resistive barrier that also provides high R-value and breathability. This combination of performance benefits is what makes Halo Exterra truly unique. Check out this short video clip:

Installation Steps to Maintain the Water-Resistive Barrier Capabilities of Halo Exterra

Here are the installation steps to maintain the water-resistive barrier capabilities of Halo Exterra:

  • Choose a thickness of 9/16” or greater.
  • Tape over all fasteners.
  • Tape over all joints.
  • Tape over all penetrations.
  • Use both tape and spray foam for larger gaps.
  • Avoid damaging the laminate on Exterra.
  • Tape over any sections of damaged/cracked laminate.
What Installers Say About Halo Exterra as a Water-Resistive Barrier

Since August of 2018, Anthony Dew of Stalwood Homes has built 42 custom units with Exterra ranging from 900 sq. ft. to 7,500 sq. ft. in Cobourg, Grafton, Brighton and Baltimore.

He originally met a Logix Brands team member at the Cobourg Rona Show (he always buys from Northumberland Building Supplies). According to Anthony, “Exterra is his singular go-to exterior sheathing.” He’s also a big believer in offering a wall assembly with a layer of continuous insulation.

Anthony also uses a 3M double-sided 4” wide sheathing tape with 2” peel off sections for easy overlap.

Here’s why Anthony builds with Halo Exterra:

  • UV Resistant Coating = Added Convenience

Scheduling delays always happen, and the UV resistant coating makes it possible for Exterra to remain exposed. While you can tape it right away, you can also tape three weeks later or whenever it’s convenient for you.

The problem with XPS, for example, is that it gets flaky when exposed to UV rays, which makes taping difficult. In this way, Anthony says XPS is “not real-world friendly” like Exterra is. It simply doesn’t work as well in normal working conditions.

  • Price Competitive

Anthony also likes that Exterra is competitive with other options on the market.

  • Canadian-Made and Local

As a Canadian himself, Anthony likes that Exterra is not only Canadian-made, but also local.

(Halo products are manufactured in six locations across Canada and the USA.)

Wrapping it Up

Halo Exterra is designed as a water-resistive barrier due to its thickness and laminate.

However, Exterra is not only a water-resistive barrier. It’s also breathable, while still offering a high R-value, and this is what makes it a unique product on the market (while still being price-competitive).

But that’s not the only reason why installers love Halo Exterra. Anthony Dew of Stalwood Homes loves its UV-resistant coating and price competitiveness as well.


New Owens Corning High-Performance Exterior Wall System

Wed, 2019-08-21 09:50
Energy Efficiency

Sto Corp., the innovative world leader in full system facades, prefabrication, air barriers, coatings, and restoration solutions, has recently introduced StoTherm ci Mineral, the only U.S. decorative and protective high-performance exterior wall system with the unique advantages of mineral wool. Developed by Sto Corp. in collaboration with Owens Corning, the StoTherm ci Mineral system combines the fire and thermal advantages of mineral wool with the design flexibility and performance of Sto exterior wall systems.

StoTherm ci Mineral goes well beyond the NFPA 285 standard with enhanced fire protection for improved occupant safety. With a continuous exterior thermal control layer that resists fire and temperatures in excess of 2000 degrees for more than five hours, StoTherm ci Mineral easily passes as a two-hour fire rated assembly. The StoTherm ci Mineral system has outstanding heat-transfer characteristics for occupant comfort and is the only non-combustible insulation EIFS in the U.S.

“Every element in the StoTherm ci Mineral system has been engineered to fully capitalize on the unique characteristics of mineral wool,” said Karine Galla, Product Manager for Sto Corp. “We worked with a global supplier to create the dowels, which are made of low thermal conductivity material designed to minimize or eliminate thermal bridging.”

Because mineral wool can handle much higher internal temperatures, there are no limitations on the Light Reflectance Values (LRVs) of exterior surfaces, allowing for an abundant choice from a wide range of colors, shades and textures for the exterior, giving more design flexibility. The base coat and meshes available with the system also extend a wide range of options for impact resistance.  And the system offers easy installation and a tight fit.

StoTherm ci Mineral has a fully integrated seamless air and moisture barrier and is a complete, engineered façade system with all control layers. In fact, all StoTherm ci systems, including Mineral, XPS and EPS, have comprehensive control layers including thermal, air, vapor, and water.  Durability and water-shedding control layers are also available.

For more information on how the StoTherm ci Mineral system can enhance the performance of a building project, visit


What Caused the Air Barrier Industry to Develop?

Tue, 2019-08-20 14:59
Building ScienceEnergy Efficiency

Editor's Note:  A previous EEBS article addressed the significance of air leakage control by answering the question: What’s the big deal with air leakage?

In the U.S., our understanding of air leakage through building envelopes has evolved over the course of 100 years or more. In the first application of tarred felt paper installed over 1x board sheathing in the early 1900s, it was applied to cut down on “draftiness” of conventional wood frame construction, due to gaps between board sheathing on walls and wood floor boards. This was an obvious practical matter. Since that time, things have gotten simpler and also more complex, but we are heading in the right direction. Let me explain…and this will take us through some history...

In the not so distant past, there were no air leakage provisions for buildings and this resulted in a building stock with excessive air leakage rates resulting in wasted energy, poor comfort, and other building performance issues (see previous article). With recently increased levels of insulation to improve energy efficiency and changes in building materials in relation to their moisture tolerance, the need for better air leakage control became necessary to prevent moisture problems. We’ll leave the high-moisture content and rain-water intrusion issue for another time.

It also became obvious that a proper functioning water vapor retarder was needed as buildings became better insulated, but we soon learned that a vapor retarder could not control water vapor movement if the moist air itself was bypassing the vapor retarder and getting into and through the assembly causing moisture accumulation or condensation along the way – essentially defeating the purpose of the vapor retarder. 

Eventually, this progression of practical building science knowledge and the need for better air-leakage control birthed the concept of an air barrier (or air control layer) that we now find present in our modern energy codes (but is also important for the building code from a durability standpoint). This soon begged the question of what material(s) to use and where to put it (necessity is the mother of invention). This question was answered and now we have a multitude of choices for air barrier materials, methods, and locations on the assembly. A short list of options include:

  • Building wraps
  • Sheathing materials with sealed joints (e.g., insulating sheathing, structural sheathing, etc.)
  • Fluid-applied coatings
  • Spray foam
  • Gypsum wall board
  • Film-type vapor retarders

Some of these materials are typically located on the outside of the assembly (and may also be used as the water-resistive barrier layer). Others are located on the interior side (and may also be used as a vapor retarder). Two examples for locating the air barrier (or air control layer) are shown in Figure 1. Some are even “smart” vapor retarders that hold back water vapor (and moist air) but open up when water vapor needs to pass through or get out of the assembly (ever heard of drying potential?).  So, our air barrier tool box has been greatly expanded in recent years. 

Figure 1. Interior (drywall shown) and exterior (foam plastic insulating sheathing shown) air barrier locations on a building envelope.  Both are tied to the ceiling (drywall) and foundation wall for a complete air-barrier system. Source: U.S. Department of Energy Air Leakage Guide 

We now have plenty of tools and no excuse for not meeting or exceeding the minimum air leakage control requirements in the current model energy code. The next article will address air barrier installation requirements (a prescriptive laundry list of action items). The final and fourth article will cap the series with the blower door test as the ultimate objective means to verify compliance. It’s also a cool tool to help find those pesky and costly leaks. 

For more information on air-barriers and air-leakage control, refer to

For additional information, please review the following articles and videos: