Roundtable:
Thermal Barriers in Retrofit
By Senior Editor, Mark Robins,
Posted
07/31/2012
Metal Construction News asked several industry experts
about thermal barriers in retrofit
Lee Durston, director of building science division. BRCA Inc., Tacoma, Wash.
Phil Effler, sales engineer, Technoform Bautec North
America, Twinsburg, Ohio.
Dan Harkins, CEO, Thermal Design Inc.,
Stoughton Wis.
MCN: What are the differences between
thermal barriers for building retrofit vs. thermal barriers in new
construction?
Dan Harkins: "Thermal barriers" are defined for
the purposes of this roundtable as "insulation systems" that
inhibit the transfer of heat energy through the building envelope,
roof and/or wall assemblies.
Whether for new construction or retrofit applications, the basic
requirements of insulation systems are generally the same, although
in retrofit applications there may already be thermal breaks, air
barriers and existing insulation, which are typically left in place
and added to.
The major difference between a retrofit installation and a new
installation is often installation from the interior. Obstructions
on the floor typically set the pace. Experienced crews can whip
through the retrofits fairly quickly if the floor area and wall
areas are mostly clear of obstructions. Items attached to the
ceilings and walls are usually fairly typical, predictable and
generally easy to work with.
The decision to retrofit a thermal system into an existing
building often is done for economic reasons and therefore the least
expensive means to achieving the performance required becomes the
most desirable option. Other factors, such as improving the
interior appearance, improving acoustics, lighting systems
redesign, solving interior condensation problems and others often
provide added incentives to support interior retrofits. Reports of
increased worker productivity, quieter working conditions, better
lighting and more pleasant work environments often follow interior
retrofits.
Lee Durston: In new construction you are able
to carefully design the complete envelope system including the
thermal barrier, whereas in a retrofit scenario you are looking to
add a thermal barrier to an already existing system, which can
prove to be more complicated. Any change made to the system
thermally can have major impacts on the overall performance of all
wall systems.
Phil Effler: Thermal barriers for retrofit
require greater customization to meet the aesthetic and performance
targets of the architect and building owner. Often, they use more
complex profiles to accomplish these targets as well.
MCN: What are the most common types of
thermal barriers for building retrofit today and how do they aid
the building?
Durston: Thermal barriers or insulation can be
broken down into four main categories: loose fill, blanket or batt,
foams and boardstock. Loose fill insulation is made up of a loose
pellet or fiber mix, and is blown into the building using special
types of equipment. It can be synthetic, or made of a natural
material like recycled cotton and wool from the fiber industries.
There are also fiberglass and rock wool loose fill insulation,
which are blown into the open stud cavities. Generally, loose fill
types of insulation have R values of about R-3 to R-4 per inch of
depth, while cellulose has about 30 percent more insulating value
than a rock wool variety.
Blankets and batts are the least expensive types of insulation,
and probably the most common. Made either from processed fiberglass
or rock wool, they're used to insulate the areas above ceilings,
below floors and inside walls. R-values for this kind of insulation
are about R-3 per inch in thickness. Rigid board can be made from
polyurethane, fiberglass or polystyrene. This substance comes in
many thicknesses and has an extremely high insulating value of
about R-4 to R-8 per inch of thickness.
Foam insulation comes as a two-part liquid: the polymer and the
foaming agent. Usually, the polymer in this case is a modified
urethane, or a polyurethane. This liquid is sprayed into the
cavities in walls, ceilings and floors, and expands during
application, becoming a solid plastic filled with lots of tiny
air-filled cells. This makes it easy to fill unusual spaces.
Installing insulation of this type must be done by a professional
with dedicated equipment for mixing, measuring and spraying.
Foam insulation costs more than traditional batt insulation, but
can be cost effective anyway due to ease of installation and the
air sealing benefits that are inherent with this product.
Harkins: One of the most common and most
cost-effective types of "retrofit thermal barriers" is a fabric
liner system that spans building bay (beneath the purlins) on a
support strap platform and is sealed to the perimeter structure.
These are very economical, lightweight, flexible materials, which
makes them easy to install. The fiberglass or cellulose insulation
is simply installed on top of the liner system to finish the
installation. It's a similar concept in the walls. A single-piece,
flexible, fabric liner spans the width from column to column and
floor to ceiling (inside plane of girts), and is mechanically
fastened and sealed. Both the roof and wall retrofit is done on the
building interior keeping the original metal panels on the exterior
of the structure.
The fabric liner systems provide a superior sealed system to the
roof and the walls, which is not practical to achieve with faced
fiberglass insulation. This is because of all of the seams and
extra materials and labor required to effectively seal all seams.
These are very common, effective and some of the least expensive
systems to increase the thermal performance of the building
envelope.
Effler: Thermal barriers made from polyamide
are the most common type used today. With approximately 90 percent
of the market globally, polyamide thermal barriers are used to help
improve the efficiency of fenestration products around the world.
Thermal barriers work by reducing energy transfer through an
aluminum frame, which also improves resistance to condensation.
One of the most important criteria in building retrofit today,
regardless of geography, is energy efficiency. Due to the high
ranking of energy efficiency, polyamide structural insulating
strips in aluminum windows are the preferred systems. These systems
offer both customized designs and high energy-efficient
performance.
MCN: How are retrofitted metal buildings'
energy efficiency and LEED standings affected by thermal
barriers?
Effler: Thermal barriers decrease the overall
energy consumption of a building, which aids greatly in meeting the
"Minimum Energy Performance" requirements for buildings pursuing
LEED certification. Thermal barrier demand worldwide has increased
dramatically over time and continues to do so every year. The use
of thermal barriers in nonresidential buildings has continued to
increase every year according to industry market studies,
especially in the curtainwall and façade segment. These systems
offer lower condensation on window and glass surfaces, and
significant reductions of HVAC loads and building operations and
maintenance costs.
Durston: By providing a thermal barrier in the
building envelope you are able to thermally separate the indoor
space from the outdoor space. The more effective the thermal
barrier is, the less work has to be completed by the inside space
conditioning system, such as mechanical heating and cooling. This
translates to energy use reduction.
Harkins: There are a variety of areas within
the LEED program where retrofitted thermal barriers come into play
especially in metal buildings. For example, there are prerequisites
for the minimum energy performance of buildings. Depending on the
building's age, the real insulation levels and the thermal barrier
integrity may need to have improvements made. Making these
improvements escalates the LEED points available when optimizing
the building's energy efficiencies to various tier levels. Most
metal buildings have a huge opportunity for energy savings due to
their obsolete insulation methods and drastically overstated
performances.
Indoor air quality is another LEED area to be addressed where
minimizing the amount of chemical emitting materials containing
formaldehyde and other VOCs is of concern. Regional sourcing of
materials and recycled content always plays a role in the design
considerations in retrofit or new construction. Essentially
anything coming in or coming out of the project site is considered
with LEED and that directly impacts buying decisions.
If success is measured in the amount of LEED projects, then I
would consider it a growing success. The number of LEED projects
continues to grow and the immediate future seems to be very
fruitful for those involved. Energy efficiency should be the first
to be exploited however, as it provides a financial payback, as
well as the simple environmental and social benefits.
MCN: Older buildings are more ventilated
than today's modern tightly enclosed buildings. Is this a challenge
and what influence does this have when installing retrofit thermal
barriers on them?
Effler: When considering a retrofit,
essentially the building envelope is being buttoned up when the new
system is installed. Specifically, thermal barriers involved in
fenestration products will likely be used more, increasing the
overall efficiency of the building envelope. Air infiltration is
only a concern if products are installed incorrectly. Updated
methods to address air infiltration include new barrier systems,
such as spray-applied systems, which seal the building more
effectively and address the window-to-wall interface. Aluminum
systems with polyamide structural insulating strips contribute to
higher structural performance. This also contributes to reducing
air infiltration, which may cost a building up to 30 percent of its
energy usage.
Durston: As we add or enhance thermal barriers
in the building envelope we change the dynamics of the system. Some
barriers can be vapor barriers that stop vapor diffusion, and if
this occurs, vapor is allowed to condense in the wall system.
Hygrothermal modeling, or vapor transition analysis, can be
completed prior to new construction or renovation work to ensure
issues like this will not be built into the building.
MCN: Are there any new codes, standards,
laws or regulations affecting thermal barriers in building
retrofit? What are they and what are their impacts?
Durston: Worldwide energy codes are
acknowledging the need for increased insulation in buildings. It is
not uncommon to see R-40 wall systems along with R-60 roofing
systems. The danger in this is knowing how to properly design with
these enhanced thermal barrier systems.
Effler: Energy codes have come a long way in
the last 10 years and are continuing to become stricter. As more
stringent energy codes become readily adopted by state and local
governments, demand for high-performance thermal products will
rise. Both retrofits and new construction are impacted by changes
in building codes.
Harkins: More and more states have adopted and
implemented newer energy codes such as the 2009 IECC (International
Energy Conservation Code) where the levels of the thermal envelope
have increased. Retrofitting may include bringing the thermal
envelope up to current code levels. It is important to understand
what the minimum intended requirements are of the new code and how
it affects your specific project and design.
The new 2012 IECC takes steps further whereas the thermal
envelope requirements increased even more than the 2009 version and
perhaps more importantly, requires the use of an effective air
barrier in most climate zones. The mandatory air leakage
requirements outlined in the new code will push installers to be
more meticulous with product installation. They'll have to rely
more heavily upon manufacturers and suppliers for technical
guidance and for proper installation techniques to ensure a quality
thermal and air barrier is achieved.
In terms of the ASHRAE Standard 90.1, a new addendum is
anticipated to be approved and publicly available by the time this
round table is published in August. This addendum is the popular
'addendum bb' where large steps towards energy efficiency have been
incorporated for a variety of building elements regardless the type
of building structure. This new addendum to the 90.1-2010 Standard
is of specific interest to the metal building industry because it
will incorporate for the first time, the revised Ufactors for the
"traditional" single and double layer fiberglass assemblies as
typically installed.
MCN: What is a "deep energy retrofit" for
buildings and how are thermal barriers a part of it?
Durston: It is imperative to address the envelope's thermal
barrier during a deep energy retrofit. The largest part of a
building's energy usage is space conditioning. By increasing the
thermal barrier, you are reducing the need for space conditioning
reducing overall energy consumption.
Effler: The idea behind a deep energy retrofit
is to reduce the overall energy a structure uses by taking a whole
building approach. The built environment increasingly understands
the importance of optimizing the energy efficiency of the building
envelope before engineering the building systems and
infrastructure. Except for the mildest climate zones, the use of
thermal barriers apply very widely to the building envelope changes
that are being made when doing a deep energy retrofit. Substantial
improvements in whole building energy efficiency are only possible
when the thermal performance of the glazing system is
optimized.
Harkins: From what I understand, the term deep
energy retrofit analyzes the building as a whole. It then looks for
synergies within new and existing systems to exploit and take
advantage of to help further reduce energy usage. Far too often in
today's market, contractors focus retrofitting on a
component-by-component basis, rather than looking and implementing
strategies that integrate total energy design savings. For example,
next time your company has an opportunity for retrofitting the
insulation in an existing building, also look for other areas the
building owner can save energy. These could include more efficient
HVAC, alternative doors or windows, automated controls for
daylighting or occupancy, and a lighting upgrade. These are all
areas to explore as a whole energy package that complements one
another and works as a system, not a single component at a
time.