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Hybrid Insulation Systems Provide Efficient, Cost-Effective Blend of Air, Thermal and Moisture Control


With today’s rising energy costs and increased emphasis on sustainability and energy efficiency, more building owners want their properties to meet the requirements of green building standards and the International Energy Conservation Code (IECC). The insulation contractor handles many of these needs by ensuring the building’s insulation meets the specified R-value, and that points of potential air leakage or moisture intrusion are properly sealed off. Of course, there are a variety of ways to accomplish this.

Caulking under baseboards and along wall stud seams, in addition to insulating around rim joists using closed-cell spray polyurethane foam (SPF), can provide effective air seals in areas traditionally known for air leakage or moisture intrusion. Closed-cell SPF can also be used to fully insulate the entire exterior wall cavity for ultimate thermal, air and moisture control. Contractors can give customers similar performance, but at a lower installed cost, by implementing a hybrid insulation system strategy.

Hybrid insulation systems combine two or more insulation products, utilizing the products’ best attributes, to provide a cost-effective airtight seal around buildings, as well as high thermal and moisture resistance. In this article, we’ll look at some components of a high- performance hybrid insulation system strategy and what each contributes to the ultimate goal of a more sustainable building envelope.

Weather-Resistive Barrier
The first component of a high-performance system from exterior to interior is a weather-resistive barrier (WRB), also known as building wrap. The WRB is installed directly under the exterior cladding, over the exterior sheathing, and acts as a full wall flashing to mitigate the infiltration of bulk moisture from the exterior. As an added advantage, it also allows interior water vapor to escape from the building’s wall cavity to help promote drying.

Continuous Insulation
Continuous insulation covers the entire exterior wall, including structural framing members. Often placed between the sheathing and exterior cladding, it reduces energy loss by providing a thermal break in the wall and, depending on installation detail, impeding air leakage. Though the most common choice for continuous insulation is a foam board — usually expanded polystyrene (EPS), extruded polystyrene (XPS) or polyisocyanurate (PIR) — there are other ways to achieve this objective. One lesser-known, but effective, alternative is high-density rigid fiber glass board.

Rigid fiber glass, proven in countless commercial applications, has the same advantages as polyfoam, such as easy installation and high thermal performance. It has the superior fire resistance of the two materials and also tends to be more solid and slightly less expensive. In regards to thermal resistance, the R-value per inch of rigid fiber glass board is comparable to that of standard polyfoam boards — fiber glass rates slightly above R-4 per inch, with EPS at R-4 per inch and polyisocyanurate at about R-6 per inch.

Closed-Cell SPF and Blown-in Fiber Glass Insulation
Made from polyurethane, closed-cell SPF insulation offers a thermal resistance of up to R-6.4 per inch of installed thickness — one of the highest insulating values available on the market today. It has a higher density than open-cell SPF and is therefore more durable, with a higher R-value and a stronger resistance to moisture and vapor flows. These attributes make it the preferred SPF material choice for high- performance hybrid systems. Closed-cell SPF is sprayed as a liquid into the wall cavity and expands via chemical reaction to up to 30 times its initial volume, filling crevices, gaps and other hard-to-reach spaces. This creates a very effective air barrier and vapor retarder. In addition to being a high-performance, multi-functional insulation material, SPF applied to exterior walls and attic ceilings provides additional structural support and racking strength.

The combination of SPF and fiber glass insulation in the wall cavity as part of a hybrid insulation system provides an air seal similar to a full cavity of SPF at a significantly lower installed cost. This strategy consists of a 1- to 2-inch flash coat of closed-cell SPF against the interior surface of the exterior sheathing, with blown-in loose-fill fiber glass insulation filling the remainder of the cavity. Fiber glass batts can also be used in these strategies, but you will need to work slowly and carefully to ensure the same perfect fit that one gets with blown-in loose-fill insulation.

Smart Vapor Retarder/Air Barrier
The final step of a hybrid insulation system strategy is applying a polyamide film “smart” vapor retarder and air barrier that has the ability to change permeability with ambient humidity conditions. With a high resistance to water vapor permeance at low relative humidity levels, a smart vapor retarder protects the hybrid insulation system as much as traditional poly or kraft vapor retarders. But, unlike traditional solutions, it reacts to high relative humidity by increasing its pore size, allowing water vapor to pass through it. The product is also able to form an interior air barrier system when combined with recommended tapes and sealants.

The smart vapor retarder and air barrier is typically installed on the interior side of the insulated wall, over the fiber glass insulation, for maximum moisture protection. It is important to consult state building codes before installing, as vapor retarder placement can vary between climate zones.

Hybrid insulation systems offer plenty of bang for the buck. They present a cost-effective strategy for meeting or exceeding the thermal, air and moisture resistance requirements of the IECC and LEED® v4. And, most importantly, the customer will get a building with lower utility bills and a more comfortable interior with higher indoor air quality. The benefits of these systems are substantial and are excellent selling points to the building owner who wants sustainability for the best price possible.

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