The Importance of "As-Installed" Insulation
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
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
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
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
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.
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