Deep Energy Retrofit Profile: |
Castle Square Apartments on Track to Reduce
Energy by 73%
Largest Deep Energy Retrofit in the U.S. Ever Completed
Located in the vibrant community of the South End of Boston, Castle Square
Apartments, built in the 1960s and a product of urban renewal, resembled
many such affordable housing developments built during that time across the
country: brick with concrete infill, no insulation in the walls and minimal
insulation on the roof.
Being 50+ plus years old, Castle Square was scheduled for renovation in
2009. The renovation would include updating the heating and cooling systems,
hot water, install new windows and roof, and updating the kitchens and
baths. Federal Low Income Housing Tax Credits were available for the
Clark, Biome Studio Principal, had been involved in many green renovations
for other WinnDevelopment properties, the minority owner of Castle Square.
The renovation for Castle Square would be a “green renovation” for energy
Passionate about energy savings, Clark knew energy savings from a standard
green renovation on Castle Square would result in around a 30% energy
savings. However, Clark knew Castle Square presented the perfect opportunity
for a different type of renovation that would generate more aggressive
energy savings. “In Europe there are examples of projects reaching much
greater savings. Deep Energy Retrofits are used frequently in Europe and in
some cases have saved more than 90%. Deep Energy Retrofits have been
completed in the U.S. however one has never been done in the U.S. of this
size,” explains Clark.
Deep Energy Retrofit (DER) produces larger energy savings than conventional
green renovations. DER’s produce 50% or more energy savings through highly
insulated building shells, high-performance windows, lighting, advanced
building systems and controls. While a conventional energy retrofit focuses
on isolated systems, a Deep Energy Retrofit takes a whole-building approach
for optimal building performance.
The Castle Square Tenant’s Organization (CSTO) was open to this new concept.
As majority owner, CSTO had struggled to retain affordability, having faced
the threat of its rents going to market rates at one point in the 1980s.
CSTO managed to acquire the property, establishing affordable rents for the
next 100 years and helping secure the diversity that is the South End’s
heritage. “It was the members of CSTO who pushed for a deep energy retrofit
from the beginning,” says Clark.
The residents of Castle Square two largest complaints were 1) poor
ventilation and 2) uncomfortable conditions – their homes were either too
hot or too cold. Investigation showed there was extensive air leakage
between apartments and the outdoors, and the windows were poorly insulated.
The complex was serviced by four central boiler rooms (each serving 48
apartments) with large, oversized atmospheric boilers and indirect hot water
heaters. The apartments had hydronic baseboard heat and individual
through-the-wall air conditioners.
In addition to poor ventilation and uncomfortable conditions, residents
didn’t feel a part the South End of Boston. According to CSTO President and
resident Ann Moy, “in some ways, we felt alienated from our community. The
look of affordable housing made us feel separate from the increasingly
affluent neighborhood of South End.”
“The residents of Castle Square wanted cutting edge green technology in
their renovation, but just didn’t know how to get there,” related Clark.
“Once we presented the Deep Energy Retrofit concept and how it addressed all
the building’s concerns it was backed by the residents and we received 100%
approval from the CSTO board.”
Additional funding was needed for the Deep Energy Retrofit. After a lengthy
process Clark and the team secured funding for the 192 units and retail
space on the first floor from the 2009 American Recovery and Reinvestment
Act, through the Massachusetts Department of Energy Resources High
Performance Grant Program and the U.S. Department of Housing and Urban
Development (HUD). (For a complete list of financing go
The Principles of Castle Square’s Deep Energy Retrofit
To achieve an energy savings of more than 50% and address the residents’
concerns, the design team of Elton + Hampton Architects, Building Science
Corporation, Biome Studio, Petersen Engineering, CWC Builders, and Pinck &
Company focused on six principles:
Super Insulate. A new super insulated shell, combined with a
super insulated reflective roof, high efficiency windows and extensive
air sealing will increase the insulation value of the building by a
factor of 10.
Air Seal. Without air sealing to stop leaks, insulation doesn’t
work very well. Air sealing is as simple as caulking cracks and holes to
the outdoors and between apartments. It also limits the stack effect,
reduces pests and improves indoor air. The super insulated shell and air
sealing is projected to drop heating by 61% and cooling by 68%.
Scale Down Heating & Cooling Equipment. A super insulated and air
sealed building requires only a fraction of the energy to heat and cool.
High efficiency heating equipment will drop the building’s heating needs
by 10%. Insulating pipes and high efficiency boilers with indirect hot
water heaters will drop hot water energy usage by 41%.
Improve Indoor Air Quality. Indoor air quality is expected to
increase substantially with the use of fresh air trickle vents and
renovating the existing ventilation system with Aeroseal and CAR
Harness the Sun. Solar thermal for hot water can reduce a
building’s energy usage. Hot water energy use is expected to drop by 37%
due to the solar hot water system.
Reduce Plug Load. Using Energy Star® appliances, fluorescent, and
LED lighting fixtures can decrease an existing building’s energy usage.
Energy use of refrigerators and lighting is expected to drop by 53%.
Results. The Castle Square Deep Energy Retrofit is expected to
reduce total building energy consumption by 73%.
Kingspan’s Super Insulated Shell
The super insulated shell of Castle Square is an insulated metal cladding
over a mineral-fiber blanket backed by a fluid-applied air and moisture
barrier, attached directly over the original walls of the un-insulated brick
and concrete. This shell will deliver the bulk of the high-energy savings
while also beautifying the neighborhood. Using the super-insulated shell
concept also allowed the tenants to remain in their homes during the project
with minimal disruption.
The four seven-story buildings of the complex were literally wrapped in the
super-insulated shell. The project team selected Kingspan’s Mini-Wave and
Micro-Rib panels from Kingspan Insulated Panels North America. The panels
provide an insulative value of R-41, twice what current codes require. The
5-inch Kingspan panels accomplish the deep energy retrofit’s enclosure goals
while furnishing the building with its beautiful and durable new facade.
design team considered other exterior shell options before selecting
Kingspan. They found using the interlocking panels by Kingspan no
scaffolding would be needed generating a large cost savings. It was more
affordable than other systems, and the system was interlocking, that by
minimizing thermal bridging which was a huge plus in the shell.
“Kingspan’s insulated metal panels (IMPs) installed on the Castle Square
project provide a single element exterior cladding solution, optimized
thermal efficiency, and ideal for “Deep RetroFit” applications. IMPs are
factory assembled wall and roof cladding components consisting of a polyiso
insulation core sandwiched between interior and exterior steel skins with
factory-formed joints allowing quick installation. The combination of a
monolithic panel assembly and integrated joints allow IMPs to function as
the vapor, moisture, and air barrier in addition to providing excellent
thermal performance. Thermal continuity and performance is achieved across
the entire building envelope and the strength of the composite panel allows
attachment to steel framing with minimal thermal bridging. The energy model
for the Castle Square project showed energy cost savings of IMPs and
resulting ROI exceeding that of solar panels,” explained Paul Bertram, FCSI,
LEED AP, Kingspan’s director of Environment & Sustainability.
“Kingspan was great to work with and supplied a level of understanding and
compassion for the project that went above and beyond,” relates Clark.
The visual transformation of the building continued with high-efficiency
windows (R-5) combined with a super insulated reflective roof (R-40). The
existing ballasted roof was removed and taken down to the original
insulation. More insulation was added to the existing insulation bringing
the roof up to R-40 and the new super insulated reflective roof was
“Windows during the original renovation were going to be sliders but changed
to casement windows for the DER. Casement windows are much tighter and more
efficient. During the planning in 2009, R-5 windows were not very common and
were hard to find. Thankfully they are easier to get today,” said Clark.
address the tenants’ complaint of air quality the team viewed each apartment
as an individual house. They needed to figure out how leaky the building was
and how best to seal those leaks. The team opened walls and windowsills.
Scopes were run through the ductwork. Building Science Corporation also used
a tool called a blower door test. This special calibrated fan sucks air out
of the building and simultaneously measures how fast air leaks back into the
building. During this process, leaks can actually be felt and overall air
leakage in the apartment was measured.
Building Science Corporation’s knowledge guided the team in sealing all
holes and pockets in the walls and floors of each apartment treating each
apartment as a compartment. Their knowledge of “air sealing” the apartments
was instrumental in good design. The existing exhaust ventilation system was
renovated utilizing Aeroseal technology and fresh air trickle vents were
installed. Trickle vents on the exterior walls replaced the existing fresh
air system. No more cooking, smoking or other odors leaking into adjacent
energy modeling by Building Science Corporation, U.S. Department of Energy’s
Building America Technical Provider, Elton + Hampton Architects and Petersen
Engineering estimated the annual energy use for the building with the
super-insulated shell and air sealing. The extensive energy modeling
calculated the building’s heating requirement and determined a smaller
mechanical system. The savings in the new mechanical systems costs helped
pay for the super insulated shell and air sealing that help reduce the
building’s heating and cooling needs from the get go.
Each building has 756 square feet of solar collectors. The independent
systems will offset 65% of the annual domestic hot water energy costs of the
construction finishes and a building has been turned over to the owner and
maintenance staff, there is a risk the building may not operate as it was
designed, especially in buildings where new technologically advanced
equipment is used. To avoid this scenario the Castle Square team made design
simplicity one of its top priorities. By focusing on reducing HVAC needs
through building enclosure (tends not to break over time – no moving parts),
rather than complicated mechanical equipment, the maintenance staff simply
has less to learn. And as the building is compartmentalized, as a result of
air sealing, it is difficult for one resident to throw the whole building
off due to poor operation (such as leaving a window open), because stack
effect is reduced.
Total Cost versus Incremental Cost
The cost of a Deep Energy Retrofit can be analyzed in a number of different
ways. The total cost of the work (labor & materials) from start to finish.
The total cost of the Castle Square Deep Energy Retrofit was $8,177,783 for
192 apartments or $42,593 per apartment. This includes the cost of
everything related to heating, cooling, and hot water. In this analysis, it
does not include the cost of high efficiency lighting and Energy Star®
Incremental cost is defined as the difference between cost of work that
would have been done anyway and the Deep Energy Retrofit scope of work.
Castle Square was to be renovated therefore the total incremental cost of
the Deep Energy Retrofit at Castle Square was $3,460,486 for 192 apartments
or $18,023 per apartment.
The retrofit of Castle Square Apartments was completed in June 2012. The
residents are happy and participation in the tenant’s organization has risen
dramatically since the project began. “The concept of the Deep Energy
Retrofit is new to many professionals in architecture and construction. The
residents at Castle Square Apartments know what it is however. They have
achieved it by being active participants, and Kingspan is proud to be a part
of this unique project,” relates Bertram. “Tenants tell us they’re now very
proud of the multi-family building’s look and are seeing their utility bills
“Special recognition goes to Deborah Backus, CSTO’s executive director, who
worked tirelessly to see this project completed,” relates Clark. Deborah
Backus was a former resident of Castle Square and one of the founders of
Castle Square Tenants Organization, Inc. She served on the executive Board
of Directions for 8 years as Co-President. “CSTO and WinnDevelopement is not
just about the building, it’s also about the quality of life for residents
that make Castle Square unique,” says Backus. Backus is founder of Backus
Associates, specializing in nonprofit resident associations with owner
representation on refinancing and renovation, asset management, leadership
development, and social and educational program development.
Castle Square is currently tracking LEED® Platinum status and recently won
the Vanguard Award from the National Affordable Housing Management
Association (NAHMA). The Vanguard Award is given each year in order to “to
recognize newly developed or significantly rehabbed affordable multifamily
housing communities that showcase quality design and financing.” Also Boston
Mayor Thomas M. Menino presented the Castle Square Tenants Organization and
WinnDevelopment with the 2012 Green Residential Award Climate Leadership.
Deborah Backus received the Arthur F. Howe Community Service Award, which is
given to an individual who has made “enduring contributions toward improving
and preserving Boston’s unique and historic South End.” For more information
on Castle Square visit