Complete Air Barrier
By Gabe Farkas, P. Eng.
Looking back over the past 100 years, one can see an interesting trend in the construction industry. Buildings erected more than a century ago are still in existence and fully functional, and despite all the advances in construction technologies, we accept the premise that newly constructed buildings should have a life expectancy of just 50 years!
While it is true the demands placed on today�s buildings in terms of occupant comfort, climate conditions, and overall complexity are significantly greater than those of the early 1900�s; it does not excuse the fact that newly constructed buildings have a shorter functional life.
This decline in building durability can be traced to the point in time where the building industry increased the use of insulation to improve energy efficiency. However, our failure to recognize the need to effectively seal the building envelope when using insulation, combined with the minimized use of mechanical ventilation, produced a series of undesired side effects.
Inadequate air sealing and/or improper ventilation allowed condensation to occur within the building envelope and led to a rise in the incidence of mold and mildew. The direct result was poor indoor air quality (IAQ), that in some instances produced detrimental health effects on the building�s occupants. (In recent years, suspicion has arisen surrounding the link between mold exposure and the increasing rate of asthma and allergies in the United States. Additionally, it is common to see allergy/asthma incidents in the news related to insufficient air sealing contributing to mold growth.) Equally alarming was the increased incidence of premature building failure caused by moisture intrusion.
The challenge facing designers/builders in the early 1970s was to produce energy-efficient structures. What was actually built in many instances were energy-efficient structures boasting poor IAQ and reduced functional lives.
Building codes��another challenge
Compounding the challenge facing today�s designers is the fact that modern structures are built to codes representing minimum standards�products of past experiences. These minimum and often outdated standards are further compromised by the perceived need for universality in code language. The end product is a building code that is applicable ?in theory� from Florida to Maine, with no consideration for climatic, elevation, seismic, and other factors particular to various corners of the country.
There is also the situation where code changes are driven by the developments and lessons learned in cold (heating) climates then applied in moderate, humid, or hot and humid climates. Under such conditions, the challenges facing today�s designers/builders are truly formidable.
However, there is a way to construct energy-efficient buildings that maximize IAQ and ensure a long life span. The answer resides in physics, ventilation, and sealing/controlling the building envelope.
Sealing the envelope
One of the greatest enemies to the durability of a structure is water. This destructive element can enter a building in four ways. The first two methods �gravity and capillary action�are facilitated by imperfect construction/detailing techniques, and usually allow substantial amounts of water to infiltrate the building. Since these two mechanisms of moisture infiltration are highly efficient, there is usually immediate and noticeable damage associated when wet weather conditions exist.
The remaining two methods for moisture to enter the building envelope are air leakage and diffusion. These modes of moisture transport are often overlooked or misunderstood because they are less visible, and the associated damage usually takes longer to develop. Diffusion is a slow, controlled process driven only by vapor pressure differentials, and rarely causes any significant moisture accumulation. Air leakage, on the other hand, is extremely efficient in moisture transport (100 times more efficient than diffusion).
The damage begins to occur when condensation commences within the building envelope (hot, humid air contacting colder surfaces/temperatures), causing moisture accumulation and a potential breeding ground for mold, mildew, and other airborne organisms.
The control of air leakage, and subsequently moisture movement, ultimately delivers extended building durability, since structural damage caused by moisture accumulation is reduced. It also works to improve the IAQ of the building.
Air leakage control also reduces the amount of exterior pollutants and gases reaching the interior of a building. Conversely, air leakage control can also allow indoor pollutants to accumulate and reach unhealthy levels. In fact, the American Lung Association estimates that indoor air pollutants can be two to five times higher and occasionally 10 times higher than outdoor air pollution.
The correct response to this dilemma is to provide adequate ventilation for interior spaces. The incorrect solution is to build a leaky structure and permit the ventilation rate to fluctuate with weather conditions.
The final benefit in controlling air leakage is the substantial energy efficiencies that can be obtained. Studies conducted by government agencies and utility companies report random air leakage can account for as much as 40 percent of a structure�s heat loss/gain. (1)
In total, the use of an effective air barrier, in conjunction with insulation and appropriate ventilation and construction methods, will produce an energy efficient structure that is healthy and durable over long term.
Selecting the right material
Today, more effective framing methods, combined with long-lasting elastomeric sealants and gaskets, are helping achieve the objective of a sealed building envelope. However, the quest to establish an air barrier and increase a building�s thermal performance by increasing the insulation�s prescriptive R-value without fully considering the actual performance, cost, or actual incremental reduction in energy consumption is a counter-productive trend.
The R-value of insulation (resistance to conductive heat flow only) is measured by a standard laboratory test (ASTM International C 518, Standard Test Method for Steady-State Thermal Transmission Properties by Means of the Heat Flow Meter Apparatus). Insulation is given a rating establishing the maximum value under ideal and controlled conditions, but does not consider convective heat flow. When installed in a building, insulation performance is completely dependent on its ability to minimize both conductive and convective (air leakage) heat flow. If there are gaps between the insulation and other building materials allowing air leakage/flow, the effective R-value of the insulation can be reduced by as much as 50 per cent from its original rating.
If the insulation allows air flow, its energy reduction capability is seriously minimized, as is its ability to act as an air barrier.
A popular method use in the effort to minimize air infiltration is the use of a polyethylene sheet as an air and vapor retarder. Field experience has shown that using polyethylene as an air and vapor retarder without ensuring continuity can fail. On the other hand, if used solely as a vapor retarder, it performs well despite a lack of continuity.
While there are several system solutions to the air sealing problem becoming available to designers and builders, a low-density, open-cell flexible expanding foam insulation, polyicynene, is being used successfully as an air barrier minimizing air infiltration in the building envelope.
Polyicynene is a completely water-blown, two-component system in the polyurethane family. The presence of water creates a flexible open-cell structure with no emissions. The flexibility ensures a permanent seal because the material moves with the building components.
The use of water eliminates the need for synthetic refrigerant/blowing agents that leave open-cell structures filled only with air. As a result, polyicynene�s R-value is lower than rigid board-type insulation materials produced with refrigerants/blowing agents, but experiences no thermal performance degradation over time.
Polyicynene is classified as a plastic material (unfortunately, building codes do not make any further differentiation) in the Class 1 flame spread category. Application of polyicynene requires a trained, manufacturer-certified installer to ensure optimum performance.
In one quick and simple application, this material delivers predictable levels of air tightness, while potentially reducing the number of trades, materials, and costs required to achieve an equivalent result with alternative insulation air/sealing products. Polyicynene is sprayed into any open cavity in liquid form, which then expands 100 times its initial volume in seconds, adhering to all surfaces and filling all penetrations in the building envelope. This process provides the insulation and air seal without altering construction techniques or traders sequencing.
Polyicynene is also being used to reduce the potential for moisture accumulation and to encapsulate surface mold. This offers the potential for easily controlling airflow and improving IAQ.
The use of scientifically and field-proven materials such as polyicynene offers the designer almost unlimited freedom of design, improved structural durability, the ability to deliver maximum IAQ, and significant reductions in energy consumption. These benefits serve to enhance the reputation of the builder because the quality and the performance of the final products are superior.
With relatively new buildings being condemned across the nation, litigation involving all project participant, mold/mildew taking center stage in the media, and the ongoing desire to reduce energy consumption, industry professionals have an overwhelming need to consider the use of materials and air sealing practices that address these issues. To this end, professionals should consider some key benefits in adopting superior building techniques and materials into their daily practice when sealing the building envelope.
Creating air barriers with new, innovative product solutions can help builders reduce time, labor, and costs associated with caulking, foaming, etc., while providing clients with a superior structure. Builders demonstrating the long-term value of lower utility costs and the effect on re-sale value can increase the selling price of building/homes and increase profits.
Increased customer satisfaction
Offering buyers increased energy efficiency (and superior IAQ and greater comfort) increases customer satisfaction and translates into fewer callbacks.
Competitive advantages in the marketplace
New marketplace innovations enable builders/specifiers to augment their portfolio of superior product upgrades, including finishes, security systems, etc. They also have the opportunity to align their energy-efficient and healthy products with credible organizations like the U.S. Environmental Protection Agency (EPA), the U.S. Department of Energy (DOE), Envirodisic?, and the American Lung Association.
CIA Since 1979
Contractor, Insulation, Air Barrier.
Tomball, TX 77377
(C) 2022 CIA