What’s the Difference Between Air Barriers and Vapor Barriers?

What’s the Difference Between Air Barriers and Vapor Barriers?


How thick does a layer of spray foam insulation has to be to qualify as an air barrier?

Many builders using spray polyurethane foam as an air barrier often ask the question: How thick does the spray foam layer have to be to stop airflow? There’s a follow-up question, of course: Is the answer different for open-cell spray foam than for closed-cell spray foam?

As with most building science questions, there is a brief answer and a lengthy answer. The brief answer is that closed-cell spray foam needs to be at least 1 or 1.5 inch thick to act as an air barrier, while open-cell spray foam needs to be between 3.0 and 5.5 inches thick to act as an air barrier.

Schematic diagram of the ASTM E2178 air leakage test for materials

We’ll go over the full answer after we’ve presented some definitions and some data.

What is the definition of an air barrier?

The majority of construction regulations describe the term air block material as the material with an air leakage rate of less than 0.02 per square meter at 75 Pa (0.004 CFM/SF @ 1.57 PSF) when the material is tested using either ASTM E2178 or E283.

The definition was accepted in the 2009 International Residential Code as the base for the definition of “air-impermeable insulation.”

A barrier to air material must be identified in relation to the drywall. We evaluated drywall, as well and discovered that it was found that the air leakage rate of drywall was slightly less than .02. This was the foundation of our norm.

What is an Air Barrier?

Air barriers are materials made to regulate airflow between an air-conditioned (indoor) area and an undisturbed (outdoor) airspace.

Air barriers are mechanically connected with adhesive membranes, building wraps and fluid-applied materials including insulating stock, non-insulating stock spray polyurethane foam, made of concrete glass, metal and many other materials.

However, regardless of the material you select the main requirements for all air barriers must be:

  • inaccessible to air flow
  • continuous across the entire enclosure or over the enclosure of a particular unit;
  • They are able to resist the forces that might be imposed on them both during and after construction.
  • robust over the expected lifespan of the structure.

Remember that there are two types of air barriers – both interior and exterior . While they both have similar functions they each increases the effectiveness that the others provide. Air barriers for the interior air barriers stop the leakage an interior home’s air through the wall attic or cavity. They also limit the ability for humid indoor air to penetrate the wall cavity during the heat season and reduce convection losses in walls.

External air barriers prevent the air infiltration from outside air through the wall cavity, and also through the attic. They restrict the ability of humid outside air to penetrate the wall cavity during cooling seasons and stop the wind washing of wall insulation (i.e. although, if a home is as tight in the interior but it could be an open external wall as well as a top-plate which can result in significant energy loss). It’s recommended to put in both kinds of air barrier to ensure that you don’t to diminish the advantages of one while ignoring the other.

What is a The Vapor Barrier?

Vapor barriers (or vapor retarders) are materials that are used to slow down or limit the flow of water vapor in the material. Vapor barriers materials are placed in the warmer side of insulation in the building assembly according to climate conditions. In warmer regions, it will be placed on the outside and in cold climates it is located inside.

A vapor barrier could be a sheet that is mechanically attached material and adhesive membranes (depending on the composition) and fluid-applied materials such as insulating boards stock, or the medium-density spray polyurethane foam. The thickness of the material will determine if it is a vapor barrier or not.

However, Wait… You can find more

This is where things become confused. Water vapor could be transported through air leakage, however, it is possible to address this issue by putting ineffective air barriers, but not a vapor barrier.

Vapor barriers aim to regulate the rate at which vapors are absorbed into an assembly of buildings. Thus the vapor barrier does not need to be completely continuous, it does not need to be completely free of holes, doesn’t require lapping and does not need to be sealed, and so on. A hole, for instance, within a barrier would simply indicate that there is greater diffusion of vapors in the area as than in other parts in the vapor barrier.

To make it easier, think of this analogy of a wool sweater The wool sweater acts as an insulation. It keeps your body warm even when there is no air movement yet it also lets the wind flow directly through it.

A wool-blend sweater combined with a raincoat can keep your body warm, but will also retain moisture and will absorb your insulation. A wool sweater that has a windbreaker keeps you warm and prevents wind from stealing your warmth, but allows the moisture to circulate through it.

Think of the raincoat as an air barrier, and the raincoat as a vapor barrier.

In high-performance structures, air barriers and barriers made of vapor, as well being water-resistive barriers can be integrated. There are also permeable to vapor air barriers as well as water-resistant barriers which are not air barriers.

It is essential to comprehend the various functions and decide if the material serves more than one purpose. For instance, there are three, two, and even 4 air block materials in the form of a wall arrangement, however, the effectiveness of these materials will depend on the material you’ve chosen and the way you’ve connected those air barrier materials to each other.

Why Are Air Barriers Really Have a Role to Play?

Air Barriers vs. Vapor Barriers

After you’ve understood the distinction in air barriers and barriers to vapor, the more important issue is why they need to be considered? It’s a question that is being addressed by a variety of engineers, architects, contractors and even building owner-developers and the answers vary.

To begin with, air pressure and moisture control in structures have become an important and crucial element when it comes to building robust and energy efficient structures.

Air leaks can create havoc due to the fact that air does not just short circuit insulation and insulation, but air can also be also a “carrier” to unwanted elements within a house (i.e. dust, noise, and co,ld and heat). If there is a lack of control over air circulation from the outside to the inside (and vice versa) the building is at an increased chance of poor performance or a building’s failure. Moisture across the three states (vapor-liquid, and solid) poses a danger for a building.

In addition to this, there is a change in the International Energy Conservation Code (IECC), as well as a number of state energy codes, which are now requiring the inclusion of air barriers in construction codes. Additionally to this, an increasing number of municipal bodies with authority (AHJs) and trade associations for green building are urging their use. A few federal agencies and big owner and developer associations also need them.

Additionally is comfort and energy efficiency –two essential elements of sustainable design – are driving the need for air barriers across different market sectors. Take this for instance:

39 Quadrillion British thermal units (BTUs). As per the U.S. Energy Information Administration (EIA) this is the amount of energy that was consumed by all commercial and residential buildings in the United States in 2015. These BTUs account for around 40% of all energy used across the country. Additionally they are responsible for structures are responsible for around 38 percent of the CO2 emissions throughout the nation.

The data was derived from a blog article by our colleagues on Barricade Building Products. Similar to us, they are constantly working on innovations in product design to meet the constantly changing requirements of building materials that are high-performance.

The best choice to use for Seaming Air Barriers

Selecting the best house wrap is akin to choosing the best tape. In the present day of high-cost energy as well as concerns regarding Indoor Environmental Quality (IEQ), air barriers are one of the construction systems that play a an important role to play.

To create secure, healthy, long-lasting affordable, and comfortable buildings, airflow has to be controlled. The flow of air is a source of moisture that can affect the long-term performance of a building material as well as its durability and integrity. behavior in the event of flames (spread by smoke) and interior air the quality (distribution of pollutants and the location of Microbial reservoirs), and thermal energy. One of the main methods to control airflow is using air barriers.

Through essentially “wrapping” the shell of the building, air barriers (a.k.a. air sealing) make sure that the structure is shielded from the effects of airflow as well as air leakage. There are four benefits of air barriers:

1. Stopping the loss of Conditioned Air

For the majority of people, the main motive “why” to air barriers is comfort.

When it is summertime, we typically chill and dehumidify air to less humidity and temperature than the surrounding conditions. When it is wintertime, we generally warm and humidify the air to an increased temperature and humidity than the outside.

Controlling the temperature of your home is essential to ensuring comfort. It is a must to maintain a comfortable temperature. United States Department of Energy estimates that 30 to 40% of the expense of cooling and heating homes is due because of not controlled air leakage. This can affect the efficiency of other systems in the building like insulation or HVAC.

Proper air sealing reduces uncomfortable temperature fluctuations and usually results in smaller better, more efficient HVAC equipment.

2. Lower utility bills

Being able to maintain well-conditioned air means that less energy is needed to condition the air. Lower energy usage is used, which means lower energy costs. Since all systems of a building have to work together in order to increase the energy efficiency of homes The savings can be significant.

A building with a properly constructed air barrier system are able to function efficiently with an HVAC system that is less expensive since the mechanical engineer will not have to make up for a leaky structure. In certain instances it is possible that the reduction in size of the mechanical equipment and price can reduce the expense of the air barrier system, in addition to reducing costs for utilities.

3. Preventing Moisture

Anywhere air is moving the water vapor will move with it. Proper air sealing minimizes the possibility of water vapor entering the wall system, where prolonged exposure could lead to water-related issues like mold and wood-rotting which could cause costly health or structural issues. Air leakage is able to move exponentially more water through and into the enclosure that is created by diffusion of vapors alone.

4. Improved Indoor Air Quality

Air barrier systems can filter out harmful substances like dust, suspended particles and allergens as well as insects, noise, odors and more.

It is also crucial to be aware that the International Energy Conservation Code (IECC) as well as the DOE Zero Energy Ready Home program, and a variety of State energy regulations (see California Title 24) now require the requirement in the form of air barriers.

Additionally, a growing number of municipal bodies with authority (AHJs) and green-building trade associations are requesting their use. Certain federal agencies as well as large developers and owners groups have them in place.

It’s no longer a matter of whether you should use the use of air barriers, it’s instead how to create and set up top-quality air barriers that can last the tests of time. Take a look at ECHOtape’s range of seaming tape.

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