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The Importance of As-Installed Insulation R-Values



   Author: MetalMag
Location: MetalMag.com


The Importance of "As-Installed" Insulation R-Values

The technical advances and product innovations in many areas of the construction industry during the past decade are truly incredible. But as a result of this remarkable progress, some segments of the industry are falling behind and need to catch up. One of those lagging areas in metal building construction is the complex, technical process of specifying the thermal envelope for metal building systems.

The heating and cooling of a structure are crucial aspects covered by specifications. Years ago, thermal envelope specifications in metal building systems were vague, specifying only a particular thickness in inches rather than R-value. Unfortunately, similar specifications are still found today in many documents. Also, much is left for field interpretation by contractors. When ambiguous specs for the design of a thermal envelope are misinterpreted, both initial construction and annual operating costs may be higher than necessary.

Given the increased emphasis on energy conservation, along with rising energy costs and broader acceptance of the American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE) standards, there is keen interest in providing the most cost-effective insulation methods for a structure's thermal envelope. This increases the need for extremely clear, concise, and highly accurate thermal performance specs. The immense importance of these specifications underscores the need to improve existing standards, testing techniques, and automated design procedures.

Improving Performance Standards for Insulation

Most insulation specification performance problems arise when manufacturers fail to test their products "as installed," as part of the building assembly. It is simply not enough to test these products in a standard environment. The resulting R-values usually differ in each test situation. Additionally, it is difficult to determine whether the published R-values of insulation products are actually based on a hot box test (ASTM C 1363) or are merely calculated. Even if actual tested R-values are used, the tests may have been conducted at temperatures producing the best Rvalue rather than at the actual performance temperature of the structure.

The most accurate thermal value of an insulation product will be the one obtained from testing the product as installed in a roof, wall, ceiling, or floor assembly. The test assembly should duplicate the usual thermal short circuits, such as insulation compression, framing, and fasteners. In addition, the tests should be conducted at temperatures reflecting actual building environmental conditions.

A few years ago there were complaints about fiberglass "filler" blankets losing as much as half their thickness and insulation value when laminated to a vapor retarder. In response, the major insulation manufacturers introduced a fiberglass blanket that was certified and labeled to withstand the rigors of the laminating process, making it readily distinguishable from filler blanket after lamination. The new standard became referred to as the North American Insulation Manufacturers Association (NAIMA) 202-96 (Rev. 2000) Standard. The goal was to minimize the difference between the R-value stated at the time of manufacture and the R-value of the product after the lamination process.

The insulation manufacturers agreed to spray a copyrighted label onto the fiberglass, indicating the minimum R-value before lamination so product quality could be distinguished in the field. This particular insulation was made to have an average of 108 percent of the labeled R-value when shipped to the laminator so it would withstand the normal rigors of the lamination process and still retain the labeled R-value. With this new performance standard, specifiers, contractors, and owners could be assured that by simply checking the label, their laminators were using the proper insulation.

What it Costs to Heat and Cool an Insulated Metal Building

This chart on page 67 shows both the initial construction and annual energy costs to heat and cool a 20,000-square-foot manufacturing and office structure located in Des Moines, Iowa, using various amounts of insulation and methods of installation. The building must accommodate HVAC requirements for human occupancy at a density of 400 square feet per person.

The model building is a 100-footwide by 200-foot-long pre-engineered steel structure, with a 14-foot eave and a 1/4:12 inch pitch singleslope roof sloping to the south. The building has a standing seam roof and panel rib (R panel) walls with the 200-foot dimension running east and west. There are four 3x7-foot walk doors (one on each wall), four 10x12-foot overhead doors on the south wall, and six 6x9-foot windows on the east wall. The foundation is a slab on grade insulated with 2-inch 2.5lb/cu. ft. extruded Styrofoam placed 4 feet in from the perimeter and 4 feet down at the perimeter under the slab. The energy efficiency of the HVAC equipment to be used is assumed to be an 80%-efficient natural gas furnace and air-conditioning units with a 10 SEER efficiency rating. When sizing the HVAC equipment, an additional 600 cfm of air infiltration is assumed above the ventilation requirements for wintertime heating load. Other energy usage assumptions are a lighting load of 2 watts per square foot, and miscellaneous energy use of 0.5 watts per square foot.

The National InsulationAssociation (NIA) recognized the need for a post-lamination standard as well as a pre-lamination standard. This led to the development of NIA 404, Certified Faced Insulation Standard, which is tested by the National Association of Home Builders (NAHB). This third-party testing assured contractors that the laminated insulation would arrive onsite with the certified NIA R-value displayed on the roll.

Adhesive application and compression levels can vary substantially, depending on the laminating machine being used, so it is important to ensure that the laminator' equipment is NAHBcertified in compliance with NIA 404. NIA documentation regarding this certification is invaluable in avoiding liability if the insulation's performance is challenged. A list of laminators certified to produce the NIA 404 product is published by both NAHB and NIA, and can be found on their websites (www.nahb.com and www.nia.com).

In addition to determining whether the specified R-value of the insulation is "out of package" or "as installed," there are several other concerns to address when completing the design of the mechanical system, such as the building's end-use, occupancy levels, geographical location, the size and quantity of doors and windows, outdoor-air exchange rates, and air infiltration. HVAC equipment designers should use this information to accurately determine the proper equipment output capacity required for the structure.

Time for Change

Vague specifications subject to misinterpretation can lead to inefficient HVAC system performance. Obviously, the potential increase in costs to the owner as a result of applying incorrect R-values when determining heating and cooling loads can be excessive. Also, this misapplication can significantly affect the structure's initial cost, future operating expenses, and occupant comfort. Considering the current ambiguous nature of too many insulation specifications and the costs associated with improperly designed HVAC systems, perhaps it is time to consider serious change.

All specifications should clearly indicate thermal values based on installed values of complete, tested assemblies large enough to include exterior panels, purlins, girts, and fasteners. Each assembly should be tested in a guarded or calibrated hot box using ASTM C 1363, Standard Test Method for the Thermal Performance of Building Assemblies by Means of a Hot Box Apparatus. In the future, comprehensive computer-assisted model analysis could help minimize testing costs.

There is no need to condemn past specification and testing practices. Instead, efforts should be directed at examining current standards and finding testing techniques and automated design procedures that will produce more accurate information. Not only would this benefit the metal building construction industry, it would take us one step closer to achieving energy independence.


Comments: The Importance of As-Installed Insulation R-Values

Your article hits the nail head-on. As a former Insulation Specialist for the Celotex Corporation and Dow Chemical, I preached daily this information. Next to the foundation the building rests on and the building itself, the insulating system is the most important product of the project, but yet the most ignored and forgotten. At the end of the customer loses every time. Laminated fiberglass is the go to for insulation in metal buildings and no one knows why. This is a follow the leader industry. The building manufacturers follow Butler and the builders follow each other. Wise builders who know about this secret-can sell thier entire project based on or around the insulation system far above the building manufacturers brand. Laminated fiberglass for insulation is the worst insulation system for a metal building. It lacks a true vapor barrier (when not installed correctly which is about 90% of the time) is subject to heat loss through conduction, convection and radiation. And ...
By Scott Thomson
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