The multiple purposes of air barriers

Closed-cell spray foam can utilize a blowing agent to achieve around R-7.1 per inch, one of the highest values in the market.
Closed-cell spray foam can utilize a blowing agent to achieve around R-7.1 per inch, one of the highest values in the market.

Conversion to multipurpose products
Even before energy codes required an individual air barrier material, ci was already being implemented in construction. It drove the movement to remove other materials from the wall and rely on insulation to act as an all-in-one air, water, and vapor barrier. Today, ci continues to grow.

The advancements in ci materials helped engineers and manufacturers explore how to build a stronger, better wall. It provides several benefits to a building besides the elimination of thermal bridges. It increases the overall durability of the wall assembly and the building’s energy efficiency, thereby reducing the facility’s energy bill over time. If also installed as an air barrier, it can reduce the risk of condensation and moisture infiltration. The popularity of multipurpose ci products is directly related to the rise in desire from designers, owners, builders, and end-use occupants for high-performance, low-maintenance, energy efficient buildings.

Commercial buildings account for 18 percent of the nation’s energy use and greenhouse gas (GHG) emissions, according to an Energy Star Commercial Building Design report. Along with the consistently rising gas and electricity prices, builders, owners, and architects are willing to spend and invest more in their designs and buildings now in order to save on future energy bills, driving the demand for ci and air barrier products.

While product innovation in air barrier materials has evolved dramatically in the past two decades, the demand for greater efficiency will continue to drive new developments in years to come.

Benefits of using air barriers
There are several advantages to a tight building beyond just energy efficiency. Cooperation of the whole design team is required to achieve these advantages. The insulation needs to be positioned in the correct place on the exterior wall to the correct R-value per climate zone. It requires the mechanical engineer to not overdesign the HVAC system with the understanding the building will be tight. The adage of “build it tight, ventilate it right” must be implemented. It also requires the proper controls and monitoring of the interior environment so that the HVAC system can respond as needed.

Closed-cell spray foam insulation acts as an all-in-one air, water, and vapor barrier, thereby saving time and money.
Closed-cell spray foam insulation acts as an all-in-one air, water, and vapor barrier, thereby saving time and money.

Controlling humidity is a large part of indoor environmental quality (IEQ) and is crucial in commercial buildings. Uncontrolled humidity in a stud cavity can lead to mold, condensation, and even deterioration of structural components (e.g. rust). Exterior water vapor (humidity) can get into a building by either air movement or diffusion. Humidity travels most easily though air, so by first applying an air barrier in the proper place (i.e. the exterior side of the exterior wall), vapor intrusion can be prevented from getting into the wall cavity. If the air barrier also happens to be a vapor retarder, like spray foam ci, the vapor intrusion is all but eliminated. This allows the HVAC system to be designed at a lower humidity load and amounts to less work for the system. If accounted for correctly, a proper air barrier and ci combination may even lead to downsizing of the HVAC system.

 

Vapor pressure drive is from high to low just as high temperatures migrate to lower temperatures. In climate zones with more cooling-degree days than heating-degree days (mostly hot weather) the general vapor drive is from the exterior to the interior. In extreme locations (e.g. Miami and New Orleans), it makes sense to keep the air barrier and vapor retarder on the exterior side of the wall to prevent warm, humid air from entering the building.

This same design works in climate zones with more heating-degree days than cooling-degree days (mostly cold weather) when ci is employed. The proper amount of ci ensures the wall components interior of the insulation are warm and above the dewpoint temperature. Of course, ci works best if it is also an air barrier. Cold air bypassing ci is no different than using a loose-knit sweater to stay warm in windy, cold weather. The sweater is pointless if you can feel the cold air through it.

Close-up of foil-faced polyisocyanurate (polyiso) insulation.
Close-up of foil-faced polyisocyanurate (polyiso) insulation.

Air barriers work in all climates to help manage humidity, especially when they are integral with the ci. Better control over humidity means the prevention of condensation and mold, and its negative health effects.

Air barriers also help reduce sound transmission through the wall, which is a little thought of benefit. Reducing sound transmission makes for improved IEQ. Sound travels through air, but if air movement can be stopped from the outside, it essentially slows down sound. An air barrier by itself will not stop sound altogether, but it will reduce it, leading to further indoor comfort.

Air barriers are more than just a required control in building codes. While improving energy efficiency is the key purpose, their other benefits, such as helping control the interior environment, providing a durable design, and creating a high-performing building, should all be closely considered in air barrier material selection. There are many products that do not limit design, cost, or time. Understanding the options of these materials and systems will help architects and specifiers make informed decisions on selecting the right air barrier for creating high-performing buildings.

Jay Saldana, PE, is senior engineer at Icynene-Lapolla, specializing in commercial construction. Saldana brings his building science experience to architects, engineers, and designers looking to employ spray foam to help ensure building enclosures function properly and at their full potential. Saldana received his bachelor of science degree in civil engineering from Texas Tech University. He can be reached at jsaldana@icynene-lapolla.com.

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