Think of a metal wall as a combination of elements- studs, insulation, air barrier, thermal barrier, etc.-working together as a system. Selecting the right product for each can be overwhelming, especially when specifying the insulation and air barrier as there are so many different options available. Designers require products that are economical, easy-to-install, and perform over the life of the building while still meeting energy code requirements.
With THERMAX insulation and air sealing foams, such as FROTH-PAK Class A Foam Insulation* and GREAT STUFF PRO Insulating Foam Sealant* from Midland, Mich.-based Dow Building Solutions, it is possible to achieve continuous insulation and air barrier properties in one convenient package and meet energy code requirements.
Code Requirements for Continuous Insulation R-value and Air Barriers
Both ASHRAE 90.1 and IECC energy codes now recognize the importance of continuous insulation (ci), insulation that spans structural members to minimize thermal bridges other than from the fasteners and service openings. Installing rigid insulation over the steel purlins or joists minimizes the thermal shorts associated with batt insulation and ensures that the design R-value of the insulation is the actual R-value installed. In a metal building, thermal shorts can reduce the R-value of cavityinsulated wall systems by more than 50 percent.** Installing a layer of high R-value continuous insulation over the steel studs reduces the impact of the highly conductive steel. For those states following ASHRAE 90.1-2007 addendum G and IECC 2009, continuous insulation is required in climate zones 5, 6, 7 and 8.
Air barrier requirements have changed as well. Properly designed, air barriers help control the unintended movement of air into and out of a building and are critical to prevent damage to the building from moisture laden air vapor. ASHRAE 90.1-2010 and IECC 2012 mandate a continuous air barrier for all building types. Similar to determining R-value, designers have three compliance approaches to choose from. In the prescriptive option, all individual air barrier materials must have a maximum air permeance level no greater than 0.004 cfm/ft2, with caulked or sealed joints, penetration, etc. Another option requires that the assembly of materials limits air leakage to no greater than 0.04 cfm/ft2.
What Type of Insulation?
THERMAX insulation is a polyisocyanurate thermoset foam, delivering both high R-value and a higher tolerance to heat. Specific to the THERMAX insulation formulation, the addition of glass fibers along with chemical modifications, contributes to improved fire resistance properties and dimensional stability. Available in lengths up to 30 feet for ease of installation, Dow offers six different THERMAX insulations for metal buildings. These products come with different facer configurations for multiple applications including embossed white acrylic aluminum sheet on one side and embossed or smooth aluminum foil facers.
Providing almost twice the R-value (R-6.5 at 1 inch) as fiberglass batts, the R-value of THERMAX insulation is one of the highest available in the marketplace. The high compressive strength ensures durability on the job site. Because it doesn’t settle or sag, compress or fracture at the fasteners, THERMAX Insulation has been an ideal choice in metal buildings for more than 30 years. Depending on the code requirements and the type of facer, THERMAX insulation can be left exposed on the interior of the metal building, eliminating an extra layer and the associated expense. THERMAX insulation can be easily cleaned and a light white colored facer can also help to reflect light back into the building reducing lighting costs.
What Type of Air Sealing Foam?
Air sealing foams requiring code compliance Class A performance come in a range of formulations and delivery methods from large two-component kits to ‘in the can’ dispensers, designed to fill cavities, penetrations, cracks and expansion joints to form a permanent and airtight barrier in conjunction with rigid insulation. GREAT STUFF PRO Insulating Foam Sealant is ideal for sealing small gaps (less than 3 inches) around windows, doors, skylights and other building penetrations and is available in easy-to-use cans with applicators. Larger kits, such as FROTHPAK Class A Foam Insulation, can be used where wider coverage is needed such as at joint sealing applications, roof/wall junctures, in the metal roofing flutes or nighttime tie offs.
Putting It All Together
Dow offers cost-effective and field-tested methods to meet energy code requirements for continuous insulation and air barriers. The air-impermeable facers and dense foam core means each board of THERMAX Insulation qualifies as an air barrier as per ASTM E2178-03. By detailing the joints and interfaces of THERMAX Insulation with tapes, PVC joint strips, insulation edge treatments, sealants and air sealing foams such as FROTH-PAK Class A Foam Insulation and/or GREAT STUFF PRO Insulating Foam Sealant-either singly or in combination as needed- the assembly meets air barrier requirements.
It is possible to get continuous insulation and an air barrier in one package when using THERMAX Insulation and Dow’s complementary products, FROTH-PAK Class A Foam Insulation and GREAT STUFF PRO Insulating Foam Sealant. For more information, including CAD drawings, visit www. dowmetalbuilding.com.
Doug Todd is the North American commercial marketing manager at Midland, Mich.-based Dow Building Solutions. He is responsible for managing the operation and market strategy for all products and services for Dow Building Solutions serving the commercial construction market. To learn more, visit www.dowmetalbuilding.com.
*Read the label and Material Safety Data Sheet carefully before use. ** White paper, Dow Building Solutions, July 2009. ®™* Trademark of The Dow Chemical Company (“Dow”) or an affiliated company of Dow