Code Changes:
New Insulation Methods Required to Meet Codes
Brad Rowe,
Posted
04/01/2008
The U-factors for metal building insulation assemblies have been
a hot topic in the recent code development cycles within the
American Society of Heating, Refrigeration and Air-Conditioning
Engineers, based in Atlanta, and International Code Council,
Washington, D.C. As the construction industry leans toward the
desires of the market to build more energy-efficient buildings, it
is inevitable that the prescriptive requirements to insulate metal
buildings will change with the next publication of both codes,
Standard 90.1-2010 and IECC 2009.
The ASHRAE 90.1 Standard, Energy Standard for Buildings Except
Low-Rise Residential Buildings, is typically published every three
years. The next publication, Standard 90.1-2010, is targeted to
achieve a 30 percent energy savings over the 90.1-2004 Standard.
One area that the Building Envelope Committee is relying on to
reach this goal is metal building insulation for roofs and
walls.
Since 2004, buildings that are categorized "Insulation Above Deck"
have increased in insulation stringency by nearly 30 percent;
"Attic & Other" buildings have increased by more than 40
percent. Metal buildings R-values, however, have stayed unchanged
since 1999. The committee is considering modifi cations that show
about 20 percent lower U-factor (higher installed R-value) averaged
throughout climate zones 2 to 8 for conditioned buildings for
90.1-2010. There is also a possibility that the U-factors may
become even lower than the current modifications because the
committee is evaluating various insulation systems available on the
market today.
ICC is also committed to save more energy in the next version of
its code, IECC 2009. In fact, at the IECC Code Development Hearings
held in February, IECC committee members heard a proposal by the
Metal Building Manufacturers Association, Cleveland, to increase
the stringencies for metal buildings in hopes to achieve
approximately the same 20 percent U-value reduction as ASHRAE
90.1-2010.
It is yet to be determined what insulation assemblies will be
described in the codes to achieve the new U-factors, however, the
traditional method will not meet the new thermal performance
requirements for conditioned spaces. This method uses single-layer
fiberglass rolls installed perpendicularly over the
purlin-compressing the insulation when the metal panels are
installed-negating the effects of using greater pre-installed
thicknesses. The prescriptive approach would most likely require
the equivalent of two layers of uncompressed fiberglass installed
in the roof and continuous insulation in the walls, in addition to
the existing single laminated fiberglass rolls.
Members of the ASHRAE's 90.1 committee and IECC committee have
recently questioned the validity of "traditional" metal building
insulation performance from installation methods. The U-factors and
the insulation assembly descriptions that both code standards use
are supplied by the North American Insulation Manufacturers
Association, Alexandria, Va., and have been used in the ASHRAE
Standard 90.1 since 1999. These U-factors are listed in NAIMA's
publication "ASHRAE 90.1 Compliance for Metal Buildings (MB304)"
and are derived from a fi nite element analysis report completed in
the late 1990s.
Unfortunately, the only documentation remaining is a summary
report of the analysis that lacks the calculations and thickness
assumptions from which the report was generated. Apparently this
crucial information does not exist and is not subject to peer
review. A recent report published by Oak Ridge National Laboratory,
Oak Ridge, Tenn., usi ng the ASTM C1363 Hot Box Apparatus testing
method show its latest over-the-purlin test results contradict
NAIMA's MB304 values by about 20 percent
(www.thermaldesign.com/results/). This leaves an enormous gap
between reality and published performance values of assemblies
currently embedded in both energy codes.
To achieve the thermal performance (U-factors) of the insulation
assemblies listed within each code, one must first quantify how
well the insulation is performing and what nominal thickness needs
to be achieved after installation so the insulation can perform as
expected. There is little guidance from NAIMA about the thicknesses
required throughout the purlin cavity and no instruction how to
install the over-the-purlin insulation to achieve the desired
thicknesses required to achieve the advertised performance. NAIMA's
publication "Recommendations for Installing Fiber Glass Insulation
in Metal Buildings (MB316)" is limited and confusing when it comes
to details regarding "over-the-purlin" methods.
MB316 mentions keeping tension on the insulation when rolled out
perpendicular over the purlins while the roof deck is attached.
This prevents excessive drape between the purlins that could result
in large voids between the insulation and roof deck. However, these
recommendations also state: "Do not overstretch the insulation.
This can result in over-compression and reduced R-value." There is
apparently a fine line between tension and compression. These
instructions are vague and confusing enough to put the burden of
interpretation on the contractor. NAIMA needs to guide designers,
contractors, erectors and professional organizations, such as
MBCEA, by clearly defining the installed over-the-purlin insulation
thickness required across the various purlin cavities after typical
installation and to provide practical instruction of achieving
those thicknesses.
All project insulation specifications should reflect the
installed assembly R-value (overall U-factor) intended for the
building. If the installed insulation does not have verified
performance values based on field verification and hot box testing
or modeling based on hot box testing of field representative
assemblies, those projects may not meet current energy code levels.
The misleading and ineffective nature of the over-the-purlin method
is an excellent opportunity for architects and contractors to
explore other options available on the market today. Architects
should consider the installation processes for the products they
specify, realizing that certain installation methods will not
deliver the intended performance and not meet minimum code
requirements.
TOP: A cross
section of typical over-the-purlin insulation with arrows showing
the center- and quarter-points of the purlin cavity. Along with a
pin probe test at the purlins, these points aid in measuring the
average insulation thickness. BOTTOM: A typical over-the-purlin
insulation installation photo, taken for a field measurement
survey.
Brad Rowe is the national marketing manager for Thermal Design,
Stoughton, Wis.
www.thermaldesign.com; www.thermaldesign.com/results/