When to Use a Fluid-Applied Air Barrier or a Sheet-Applied Air Barrier: How to Tell

Air barriers are your first line of defense in protecting your building from moisture. Why is moisture protection so important? You can find the answer in one of the most unsettling statistics to emerge in 2016 by the Australian Institute of Waterproofing: “…water leaks and the resulting damage from water leaks accounted for up to 80% of all building defects.” Eighty per cent!

Indoor air quality (IAQ) issues from mold in remodeled and new buildings is estimated at 30% per FerroCanada. One in 50 homeowners will file an insurance claim for mold, and 93% of chronic sinus infections have been attributed to mold, with an estimated 45 million+ buildings in the U.S. having “unhealthy levels of mold.” Even Frank Lloyd Wright’s most iconic structure, Fallingwater, was nicknamed “Rising Mildew” by its original owner, Edgar Kaufman. (His son Edgar Kaufmann Jr. would later donate Fallingwater to the Western Pennsylvania Conservancy in 1963).

There’s a school of thought that only the non-traditional, parametric building designs with those undulating, twisting, non-geometric shapes designed by “starchitects” Zaha Hadid, Bjarke Ingels, and Frank Gehry should be specifying fluid-applied air barriers, but buildings with normal angles that don’t look like Salvador Dali’s melting clocks also robust need protection.

What do air barriers do?

Air barriers are like the windbreaker of your building envelope, controlling the airflow – and the moisture attached to it – between an unconditioned space (the great outdoors) and the conditioned space (your building’s interior). While preventing vapor diffusion is also important, did you know that airflow carries 50 to 100 x more moisture than vapor diffusion?

Per the Air Barrier Association of America (ABAA), an air barrier is “a material designed to control movement of air throughout the building assembly.”  Air barriers were first used in Canada as an energy conservation innovation. Today they are mandated for all federal buildings because of the energy cost savings they provide. (W. R. MEADOWS provides information on the various air barrier standards here.)

You need air barriers to provide this protection trifecta for your building envelope:

1. They prevent conditioned air leaks
2. They lower energy bills because conditioned air requires less energy than reconditioned air
3. They prevent outdoor moisture and outdoor pollutants from entering your exterior wall cavity because wherever you have air movement, water vapor will follow

How many different types of air barriers are there?

There are seven different types of air barrier materials available, also known as WRBs, or water-resistant barriers or weather-resistant barriers. These include the following:

1. Mechanically attached membranes, which allow vapor transmission
2. Self-adhered membranes (peel-and-sticks), which are water-resistant and vapor impermeable – Peel-and-stick and liquid-applied membranes are common on residential sites
3. Fluid-applied membranes (such as heavy-bodied paints or coatings including polymeric based and asphaltic based materials)
4. Closed-cell, spray-applied polyurethane foam (medium density spray-applied polyurethane foam, which typically provides insulation as well
5. Some open-cell spray-applied polyurethane foam that are of high density
6. Boardstock, which includes 12 mm plywood or OSB, panels made with a layer of sodium bentonite (a variety of clay) that expands to form a watertight barrier when it gets wet, plus a high-density polyethylene sheet that is installed on the outside of the foundation before backfilling 25 mm extruded polystyrene, etc.
7. Thermofusible materials (made with an SBS-modified asphalt that melts to the substrate) This option is used less frequently because it requires skilled installers and can be quite dangerous. These membranes are made from styrene-butadiene-styrene modified bitumen and require the use of a torch to melt the backing and soften the bitumen. The heat fuses layers together and overcomes some of the shortcomings of self-adhering membranes by providing complete coverage of joints and other details.

What Are the Benefits of Fluid-Applied Air Barriers?

Fluid-applied air barriers, while traditionally a more expensive material than sheet-applied air barriers (but that may be untrue in our strange economy), can actually end up saving money for both builders and building owners. Here’s how:

Lower Construction Costs: The building can use a smaller mechanical system for the HVAC system because fluid-applied membranes will protect the building from air leaks. Additionally, fluid-applied membranes require fewer applicators, which reduces labor costs.

Lower Building Owner Energy Costs: The Department of Energy estimates that maximizing air management will lower energy costs by 50%. The National Institute of Standards and Technology estimates the building’s gas usage will be 40% lower and the electric usage will be 25% lower. The building also realizes heightened air quality, which reduces health issues for occupants.

User-Friendly Application: An airless sprayer, paint roller, or v-notch trowel is all that the contractor needs to apply this material, which has a structural bond to the substrates, including caulked joints, flashing, and termination points. Spray-applied air barrier membranes are easier to install around penetrations, such as electrical conduits or brick ties and uneven substrates. That being said, this does require an experienced contractor who knows the exact thickness they need to apply. NOTE: An experienced applicator will use a “wet mil gauge” typically every 500 square feet to double-check the precise thickness of their application.

Coverage Integrity: This seamless moisture barrier will eliminate the issues of tearing, holes, “mis-lapped joints,” and provides stable rigidity under air pressure loads.

Product Integrity: No concerns about UV-ray degradation for up to six months, which is a concern with sheet-applied air barriers when stored outside.

What Are the Restrictions for Fluid-Applied Air Barriers?

Some fluid-applied air barriers will have application restrictions, so compare products before you specify and apply. These restrictions can include:

• Cannot be applied when the air temperature is below 40°
• Cannot be applied when your substrate is damp
• Many fluid-applied products can only be exposed to UV rays (before your exterior cladding is constructed) for a maximum of six months

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What Are the Benefits of Sheet-Applied Air Barriers?

• You can rely on a manufacturer-guaranteed, consistent, controlled thickness
• They fully bond to the substrate
• They can handle cold-weather and some companies offer extra-low temperature versions for applications
• Most have a factory edge of exposed membrane to address any inconsistency at the joints, providing a membrane-to-membrane seal

What Are the Restrictions for Sheet-Applied Air Barriers?

• Some membranes require an adhesive or a primer which adds to the cost of the overall installation
• Sheet membranes require somewhat of a smooth surface profile to ensure that they have full adhesion to the substrate
• The membrane is required to be roll pressed into place. If not, fishmouthing, or poor adhesion to the substrate and overlaps would be a concern.

Is There Ever an Instance When You Do NOT Need to Install an Air Barrier?

Some exterior surfaces are considered to be air barriers already, such as tilt-up concrete walls. W. R. MEADOWS Architectural Specialist Scott Wolff (CSI/CDT) wrote this in his recent whitepaper, The Air Barrier Debate: Permeable or Non-Permeable:

“In some cases, ‘traditional’ fluid-applied or self-adhered air barriers may not be needed at all. Typical examples of the latter include stucco, EIFS and precast.”

Now that you’re familiar with the various types of air barriers and their pros and cons, let’s identify when to use which air barriers.

When to Use Which Type of Air Barrier

When you’re choosing an air barrier, the decision to use a sheet-applied air barrier vs. a fluid-applied air barrier boils down to whether your labor costs are more critical than your material costs (although the material costs are closer together in today’s economy). The real decision you need to make is whether your building requires permeable air barriers (where water vapor can move through the film, liquid-applied or sheet-applied) or vapor impermeable air barriers which do not allow the movement of water vapor through the membrane.

Other factors for air barrier choice include:

• Building Geometry
• Substrate Materials
• The Climate Zone
• Building Code Compliance
• Air Barrier Continuity Requirements
• Air Barrier Durability
• Mechanical Ventilation Requirements
• Trades Contractors’ Installation Constraints
• Season/Time of Year
• UV-Rays Exposure Tolerance

W. R. MEADOWS provides permeable and impermeable fluid-applied and sheet-applied air barrier solutions in varied mil thicknesses to comply with all building codes and climate zones, which you can see here.

For your questions or requests for additional information on our air barrier portfolio, please contact our air barrier thought leader, Russ Snow at rsnow@wrmeadows.com or call (800) 342-5976.

 

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