TECH SOLUTIONS Hot Box Testing of Four Different Metal Building Roof Assemblies Determines Insulation Efficiency

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1 Summary Using the ASTM 1363, or hot box test, four different metal roofing assemblies were tested to determine their effective R-value versus the design R-value of the insulation. The ratio of these two values provides an indication of the relative efficiency of the insulation and provides designers guidance on what assemblies more closely match the calculated value of the insulation used in the design. A key learning of these test results is to not only look at total R-values of the insulation - always take the time to look at how it is constructed. Otherwise, you may be paying for insulation that you are not using effectively. The tests confirmed that using a layer of continuous insulation (ci) added more to the overall effective R-value than just using fiberglass batts. The relative efficiencies (the ratio of tested assembly R-value versus the sum of R-values used) ranged Summary Table from 72% to just over 83%. For example, the assembly with the one of the highest relative efficiencies and R-value combined continuous insulation with thicker thermal spacers and stand-off panel clips in an easyto-construct assembly. The only difference between modules 1 and 2 was the size of the panel clip and thermal spacer, although the overall efficiency gains by using the larger panel clips and thermal spacer were significant as they decreased the amount of compression of the fiberglass. Module 1 and Module 3 had similar efficiencies, although the R-value of Module 3 was the lowest of all four modules. These results suggest designers should use thicker thermal spacers and panel clips. Although Module 3 had a high relative efficiency, this assembly may pose construction problems as maintaining a clear 1 air space could be a challenge in the field. Module Rated R-value 1 R-13 + R-25 Fiberglass + 1 ½ THERMAX LD with 2 5/8 and 3 Stand-off 2 R-13 + R-25 Fiberglass + 1 ½ THERMAX LD with 5/8 and 1 3/8 stand-off panel clip 3 R-25 Fiberglass + R-2 Reflective Insulation with 1 Air Space + 1 ½ THERMAX LD with 1 and 1 3/8 stand-off panel clip Background Starting mid-2009, the Metal Building Manufacturers Association (MBMA) and Oak Ridge National Laboratory (ORNL) began collaboration to develop and document the thermal performance of new and innovative insulated metal building roof assemblies. Reference materials provided by Metal Building Manufacturers Association. For more information visit com. The impetus is the ongoing effort to increase the energy efficiency of building envelope assemblies, especially used in non-residential (conditioned) and semi-heated applications. Since metal buildings are used in approximately 40% of all low rise non-residential construction by square footage 1, it is important to achieve better energy performance in this type of construction. The model energy codes ASHRAE 90.1 and IECC - both Measured R-value (LSCS 1 ) R-46.1 R % R-46.1 R % R-36.7 R % 4 R-30 + R-13 Fiberglass R-43.0 R % 1 Large-Scale Climate Simulator 2 Average value of two measurements Relative Efficiency R measured /R rated Metal Building Manufacturers Association (2009) MBMA Member Market Share, 1 UNITED STATES. COMMERCIAL TECHNICAL INFORMATION 1

2 set minimum requirements for building insulation based on previously tested assemblies and on economic analyses to determine if sufficient cost savings could be achieved to offset the cost of added insulation. However, designers are increasingly being asked to deliver even higher R-values and the codes are continually being updated to reflect increases in required efficiency. To support this need, the ORNL and MBMA looked at four unique and innovative metal roof designs. The modules were tested in the Large-Scale Climate Simulator (LSCS), ORNL s large testing apparatus that can enclose entire assemblies such as a roof or wall. Similar to ASTM C1363 Standard Test Method for Thermal Performance of Building Materials and Envelope Assemblies by Means of Hot Box Apparatus, the LSCS also allows researchers to control relative humidity, sunlight, rainfall and other variables. In this case, modules were tested to ASTM C1363, commonly known as the hot box test. The test measures the steady state thermal performance of building assemblies at conditions typical to what is seen in the field. Because an entire assembly is tested including panels, clips, insulation, vapor retarders, etc., the effects of thermal bridging and common installation deficiencies can also be seen. Test Module Assemblies Module 1: R-13 + R-25 Fiberglass + 1 ½ THERMAX LD with 2 5/8 Thermal Spacer and 3 Stand-off Rated R-value of assembly R-13 unfaced fiberglass over the purlins 1 ¼ THERMAX LD at the bottom of the purlins, reflective aluminum foil facer and white facer on the exposed side. (R-value 6.5/inch) 2 5/8 expanded polystyrene (R-value 3.85/inch) 3 stand off R13 + R-25 + R-8.1 = UNITED STATES. COMMERCIAL TECHNICAL INFORMATION 2

3 Results and Discussion Although the only difference between module 1 and 2 was the size of the panel clip and thermal spacer, the overall efficiency gains by using the larger 3 (versus 1 3/8 ) panel clip and larger thermal spacer (2 5/8 versus 5/8 ) were significant. In fact, the efficiency of Module 2 was similar to Module 4, which did not use any THERMAX Insulation. Module 1 and Module 3 had similar efficiencies. To obtain maximum R-value of assemblies, results suggest thermal benefits when using thicker thermal spacers and panel clips or using a thin reflective insulation over the purlin with a 1 air space. However, because of the importance of maintaining the 1 air space in Module 3 to attain the high efficiency return, construction in the field may be a challenge. Not only does THERMAX Insulation provide a continuous layer insulation, using thicker THERMAX Insulation improves overall assembly performance. Module 2: R-13 + R-25 Fiberglass + 1 ½ THERMAX LD with 5/8 and 1 3/8 stand-off panel clip NOTE: Modules 1 and 2 were the same base assembly and only the thermal spacer and panel clip was changed. Rated R-value of assembly R-13 unfaced fiberglass over the purlins 1 ¼ THERMAX LD at the bottom of the purlins, reflective aluminum foil facer and white facer on the exposed side. (R-value 6.5/inch) 2 5/8 expanded polystyrene (R-value 3.85/inch) 3 stand off R13 + R-25 + R-8.1 = UNITED STATES. COMMERCIAL TECHNICAL INFORMATION 3

4 Test Module Assemblies, Cont. Module 3: R-25 Fiberglass + R-2 Reflective Insulation with 1 Air Space + 1 ½ THERMAX LD with 1 Thermal Spacer and 1 3/8 stand-off panel clip R-2 ESP reflective insulation with acrylic adhesive aluminum taped seams 1 ¼ THERMAX LD at the bottom of the purlins, reflective aluminum foil facer and white facer on the exposed side. (R-value 6.5/inch) 1 expanded polystyrene (R-value 3.85/inch) 1 3/8 stand off Rated R-value of assembly R-2 + R-1.6* + R-25 + R-8.1 = 36.7 * assumed R-value of reflective insulation foam backing plus R-value of 1 air space and assumed effective emittance of reflective surface of UNITED STATES. COMMERCIAL TECHNICAL INFORMATION 4

5 Key Learnings Designing any assembly based on the calculated total R-value does not always tell the complete story; designers should take the time to look at the construction details. As MBMA testing at ORNL showed, the thickness, type of spacers and even the type of panel clips can directly impact the R-value. The results suggest that designers should use thicker thermal spacers and panel clips to ensure they are getting the calculated R-value of insulation in the field. Test Module Assemblies, Cont. Module 4: R-30 + R-13 Fiberglass Rated R-value of assembly R-13 + R-30 = 43.0 R-30 unfaced fiberglass in the cavity between purlins R-13 unfaced fiberglass under the purlins Not applicable Not applicable The above information is courtesy of Metal Building Manufacturers Association (MBMA) and Oak Ridge National Lab (ORNL) For Technical Information: BLUE (2583) (English) (French) For Sales Information: (English) (French) THE DOW CHEMICAL COMPANY. Dow Building Solutions. 200 Larkin. Midland, MI Illustrations are not intended to replace the need for design by appropriate professionals such as architects or engineers. NOTICE: No freedom from any patent owned by Dow or others is to be inferred. Because use conditions and applicable laws may differ from one location to another and may change with time, Customer is responsible for determining whether products and the information in this document are appropriate for Customer s use and for ensuring that Customer s workplace and disposal practices are in compliance with applicable laws and other government enactments. The product shown in this literature may not be available for sale and/or available in all geographies where Dow is represented. The claims made may not have been approved for use in all countries or regions. Dow assumes no obligation or liability for the information in this document. References to Dow or the Company mean the Dow legal entity selling the products to Customer unless otherwise expressly noted. NO EXPRESS WAR- RANTIES ARE GIVEN EXCEPT FOR ANY APPLICABLE WRITTEN WARRANTIES SPECIFICALLY PROVIDED BY DOW. ALL IMPLIED WARRANTIES INCLUDING THOSE OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE EXPRESSLY EXCLUDED. Dow Polyisocyanurate Insulation CAUTION: This product is combustible and shall only be used as specified by the local building code with respect to flame spread classification and to the use of a suitable thermal barrier. For more information, consult MSDS, call Dow at BLUE (2583) or contact your local building inspector. In an emergency, call WARNING: Rigid foam insulation does not constitute a working walkable surface or qualify as a fall protection product. Building and/or construction practices unrelated to building materials could greatly affect moisture and the potential for mold formation. No material supplier including Dow can give assurance that mold will not develop in any specific system. Printed in U.S.A. Form No X-0212MCK McKAY UNITED STATES. COMMERCIAL TECHNICAL INFORMATION 5