Insulating Concrete Forms (ICFS): A Durable Option for Mid-Rise Construction

ABSTRACT
Combining reinforced concrete with rigid insulation, insulating concrete
forms (ICFs) provide a durable option for mid-rise apartments (Figure
1), condos, hotels, and dormitories. With increased attention to occupant
safety and comfort, design professionals can take advantage of concrete’s
inherent disaster resilience, fire resistance, and noise reduction qualities.
The thermal properties of ICFs offer building owners significant energy
savings over the long term. This article provides guidance for architects
and engineers on design and
construction basics of ICF construction.
ICF WALL SYSTEMS
ICFs combine two wellestablished
building products:
reinforced concrete for strength
and durability, and expanded
polystyrene (EPS) insulation
for energy efficiency. Typically,
ICF wall units are composed
of large molded EPS blocks,
similar to Lego® blocks, with
a cavity for concrete in the
center (Figures 2 and 3). The
blocks range in size from 48
to 96 in. (1.22 to 2.44 m) long
2 6 • I I B E C I n t e r f a ce Oc t obe r 2 0 1 9
Figure 1 – Apartment building built using ICFs. Image courtesy of Nudura.
Figure 2 – Concrete being placed into ICFs.
Image courtesy of Nudura.
Figure 3 – Typical ICF concrete wall components.
Image courtesy of Logix.
and 12 to 24 in.
(0.30 to 0.61 m)
high, depending
on the manufacturer.
The
most common
configuration
of an ICF unit
is two layers of
23/8- to 25/8-in.-thick
(60- to 67-mm-thick)
EPS panels spaced 4,
6, 8, 10, or 12 in. (102, 152, 203, 254, or
305 mm) apart. The most common cavity is
6 or 8 in. (152 or 203 mm) for most low- to
mid-rise buildings; but for taller buildings,
taller walls, or exceptionally high loading,
thicker walls are necessary. For simplicity,
ICFs are generally called out by the width of
the cavity; hence, an ICF with a 6-in. (152-
mm) cavity is called a 6-in. (152-mm) ICF,
and an ICF with an 8-in. (203-mm) cavity is
called an 8-in. (203-mm) ICF, and so forth.
ICF blocks are designed to have interlocking
teeth that hold the forms together
much like LEGOs®. Most manufacturers not
only supply straight blocks but have corner
blocks, angled blocks, T-blocks, and some
even have curved blocks (Figure 4). Most
manufacturers also provide special blocks
with brick ledges. Most companies supply
blocks that are fully assembled and ready
for installation, but some ship blocks that
are folded into a flat configuration and then
unfolded for installation. Other manufacturers
ship blocks and ties separately that
are assembled on site. Many ICF manufacturers
have special window and door bucks
made of wood, plastic, or steel to provide
rough framing around openings to fasten
window and door frames. Most manufacturers
also provide accessories such as bracing,
clamps, and scaffolding to make the
construction process more efficient.
There are some ICFs made of other
insulating materials, such as extruded
polystyrene or polyisocyanurate, and with
slightly different cavity configurations and
shapes, but ICFs made with EPS and a
flat-wall configuration
dominate. This can
be attributed to the
fact that flat-wall ICF
units are designed to
create standard reinforced
concrete structural
elements, using the well-documented
design criteria for reinforced concrete walls
that is found in ACI-318.1
EPS insulation used for ICFs is governed
by ASTM C578-19,2 Type II closedcell
foam with an R-value of 4 per inch.
Polystyrene pellets are first expanded with
steam, forming high-density beads, then
are injected into a mold to form the desired
shape. Once removed from the molds and
cured, EPS is a stable and durable material
suitable for construction. No chlorofluorocarbons
(CFCs), hydrofluorocarbons (HFCs),
or formaldehyde are used in the manufacturing
process, and there is no off-gassing.
EPS is moisture-resistant, non-absorbent,
and resistant to mold and rot. In addition,
EPS contains a flame retardant that is recyclable.
The plastic ties that hold the two sides
of the block together are generally made
with polypropylene plastic, but it does
depend on the manufacturer. They are
designed to withstand the liquid concrete
pressure during construction. Most manufacturers
design their ties to secure horizontal
and vertical reinforcing bars into
notches in the ties to minimize
the need to use tie wire. Although
different manufacturers provide
a wide range of spacing for ties,
the most common spacing is 6 or
8 in. (152 or 203 mm). The ties
have no thermal bridging, they do
not degrade or rot over time, and
all ties have furring strips embedded
in the EPS for screw-on attachment
of exterior or interior finishes.
Reinforcing steel used in ICF walls is
the same used for any other type of concrete
structure. Typically, smaller-diameter
bars are used, such as #4, #5, or #6, but
larger-diameter bars can be used for higherloading,
concentrated loads and pilasters.
In most cases, reinforcing steel is placed in
one layer in the center of the wall at as wide
a spacing as permitted by code, especially
for above-grade walls built using 6- or 8-in.
(152- or 203-mm) ICFs. For 10-in. (254-mm)
and larger ICFs, one can consider using
two layers of reinforcing—one on each face.
The objective is to minimize congestion
and facilitate concrete placement. In some
cases, steel fibers have been used in place
of reinforcing steel in ICF walls, but most
common applications use both horizontal
and vertical steel reinforcement.
Concrete is typically placed in ICF walls
using a boom-type concrete pump (Figure
5), though line pumps or even conveyor belt
equipment can be used. Specified compressive
strength used in ICF walls is designed
to meet or exceed the required structural
loading, but most common compressive
strength is either 3000 or 4000 psi (20
or 30 MPa). The recommended maximum
aggregate size is ½-in. (13-mm) aggregate
for 4- and 6-in. (102- and 152-mm) cavity
Oc t obe r 2 0 1 9 I I B E C I n t e r f a ce • 2 7
Figure 4 – Examples
of ICF wall block
configurations.
Images courtesy
of Buildblock.
forms and ¾-in. (19-mm) aggregate for 8-in. (203-mm) and larger cavity forms. The
required concrete slump is at least 6 in. (152 mm) but could be up to 8 in. (203 mm)
to accommodate pumping using high-range plasticizers and mid-range water-reducing
admixtures to achieve necessary flowability.
The concrete is typically placed one level at a time (Figure 6). In other words, ICF
blocks are stacked in the shape of the wall for a single story. Reinforcing steel is installed
as the forms are stacked. Bracing, scaffolding, and window and door bucks are installed.
Once the ICF wall is plumbed and straight, concrete can be placed in 4-ft. (1.22-m) lifts.
For example, a wall that is 12 ft. (3.66 m) tall would have concrete placed in three different
lifts by placing 4 ft. (1.22 m) of concrete at one time for the entire length of wall. By
the time the pump hose reaches the starting point, the concrete is usually stiff enough
to place the second lift, and so on.
As construction continues, electrical and plumbing lines can be embedded into the
interior layer of foam by cutting channels with a hot knife or other tool. Gypsum wall board
on the interior, and stucco, brick, stone, or siding on the exterior are common finishes
well suited to ICF construction, but nearly any finish can be applied. In most cases, interior
or exterior finishes can be applied directly to the surface by screwing into the furring
strips. Where finishes are subject to higher loading, ICF manufacturers supply special ties
that connect through the
foam insulation directly
into the concrete.
ICF FLOOR AND
ROOF SYSTEMS
There are many
options for floor and
roof systems that integrate
well with ICF wall
systems. ICF walls are
simply load-bearing
walls made of concrete,
so any floor system that
is used for other types
of bearing wall construction
can be used
in combination with
ICF wall systems. These
include traditionally
formed reinforced concrete
slabs, ICF slabs,
precast hollow-core
plank, or concrete on
metal deck, combined
with steel joists or coldformed
joists. Wood
framing systems for floor
construction can also
be adapted for connection
to ICF walls using
embedded ledger bolts.
However, there are
several manufacturers
of ICF floor and roof
systems. Just like ICF
wall systems, ICF decks
combine EPS insulation
2 8 • I I B E C I n t e r f a ce Oc t obe r 2 0 1 9
Figure 5 – Concrete is typically placed in ICF walls using a boom pump.
Photo courtesy of Quad-Lock.
Figure 6 – Construction process of ICF walls. Images courtesy of Nudura.
Step 1: ICFs are stacked in the shape of the wall, and openings for windows and doors are formed using
bucks made of treated wood or plastic.
Step 2: Steel reinforcing is placed into the forms and secured in place.
Step 3: Bracing and scaffolding are installed to keep the wall straight, plumb, and secure and to provide a
working platform.
Step 4: Concrete is pumped into the forms.
Step 5: Electrical and plumbing lines are installed into the EPS by cutting channels with a hot knife or other
tool.
Step 6: Interior and exterior finish is installed directly to the ICFs by screwing into the embedded furring strips.
with reinforced concrete to form a strong
and energy-efficient floor or roof system.
Ideal for use in both commercial and residential
construction, ICF floors combine the
strength, security, and reliability of reinforced
concrete with energy efficiency, fast
construction, and comfort. Many of the ICF
wall system manufacturers carry a version
of ICF floor and roof systems that interface
well with their wall system (Figure 9).
YOU CALL ME RAIN
HYDROTECH CALLS
ME OPPORTUNITY
Oc t obe r 2 0 1 9 I I B E C I n t e r f a ce • 2 9
Figure 9 – Typical ICF wall to floor/roof connection detail. Image courtesy of Quad-Lock.
CASE STUDY:
West Village
Student Housing at
Texas Tech University,
Lubbock, Texas
A design-build project with
Whiting-Turner, BGK Architects,
and Mackey Mitchell Architects
this 230,000-sq.-ft. (21,368-m2)
West Village student housing
complex at Texas Tech University
(Figures 7 and 8) implemented fast-track construction methods to deliver the project
within an incredibly compressed schedule—16 months for design and construction.
Opened in 2014, this $54.8-million project contains 455 beds and was designed
to meet LEED certification
serving as a model
for Texas Tech’s newly
adopted sustainability
initiatives. Expected to
reduce energy consumption
by at least 20% over
a typical residence hall,
West Village utilized ICF
walls and precast hollowcore
floors, which delivered
a highly energy-efficient,
structurally solid,
fire-resistant, and acoustically
sound dormitory.
Figure 8 – West Village Student Housing under construction.
Image courtesy of Fox Blocks.
Figure 7 – West Village Student Housing at Texas
Tech University. Image courtesy of Mackey Mitchell
Architects.
PERFORMANCE CHARACTERISTICS
OF ICF CONCRETE
Strength and durability
ICF structures are essentially reinforced
concrete structures and therefore can be
designed to resist high loading. The solid
walls act as shear walls to resist wind and
earthquake loading following the design
criteria for reinforced concrete walls in
ACI 318. ICF walls also provide protection
from flying debris from hurricanes and
tornadoes, according to Federal Emergency
Management Agency (FEMA) publication
FEMA P-361.3 Both concrete and EPS are
considered flood-damage-resistant building
materials (rated as class 5 building materials,
the highest classification) according
to FEMA, and can be used below base flood
elevation (BFE).4
Fire resistance
Most ICF manufacturers have tested
their products in accordance with standard
fire testing protocol, including ANSI/UL
2635 and ASTM E119-076. In general, 4-in.
(102-mm) ICF walls achieve a two-hour fire
rating, 6-in. (152-mm) ICF walls achieve a
3- or 4-hour fire rating, and 8-in. (203-mm)
and thicker ICF walls exceed a four-hour
fire rating. Generally, the assemblies tested
include reinforced concrete with a minimum
compressive strength of 2,900 psi (20 MPa)
3 0 • I I B E C I n t e r f a ce Oc t obe r 2 0 1 9
CASE STUDY: 17 South, Charleston, South Carolina
The builders of this 220-
unit multifamily apartment complex
(Figures 10 and 11), EYC
Companies, know that strength
and durability of the building
directly affect the safety of their
tenants. And so, they opted for
ICFs for the exterior walls for their
showcase development. Not only
are these buildings safe from high
winds and coastal flooding, but
they are extremely energy efficient, allowing EYC to master meter the entire complex
and pass the energy savings on to the tenants. In addition, EYC opted to install the ICF
walls themselves instead of using a subcontractor, which further saved time and money
during the construction process, making the project a win-win for both the building
owner and his tenants.
CASE STUDY: Hilton Garden Inn, Lewisville, Texas
With the objective
of keeping their
guests safe, secure,
and comfortable,
Hilton Garden Inn
in Lewisville, Texas
(Figures 12 and 13),
chose ICF construction
for their six-story
hotel and convention
center. Eight-inch
(203-mm) ICF walls
were used on the first
two levels, and 6-in.
(152-mm) ICF walls
were used for the top
four levels. Hollowcore
precast concrete planks were used
for the floors. The result is a fire-resistant
concrete building with the added benefits of
energy efficiency, durability, and peace and
quiet.
Figure 10 – 17 South
Apartments. Image courtesy
of EYC Companies.
Figure 11 – 17 South
Apartments under
construction. Image
courtesy of Amvic.
Figure 13 – Hilton Garden Inn,
Lewisville, Texas, under construction.
Images courtesy of Nudura.
Figure 12 – Hilton Garden Inn, Lewisville,
Texas. Image courtesy of Nudura.
and ½-in. (13-mm) gypsum wall board on
each side.
The EPS used for ICFs is manufactured
with flame retardants that render the EPS
insulation completely unable to support a
flame without an outside flame source. EPS
used for ICFs is required to have a flame
spread index of less than 25 and smokedeveloped
rating of less than 450 when tested
in accordance with ASTM E84-197 and
ANSI/UL 723.8
Energy efficiency
ICF walls are considered by the IECC9
and ASHRAE 90.110 as mass walls with
continuous insulation. Typical whole-wall
ICF assemblies have an R-value between
R-24 and R-26, depending on the exterior
and interior finish materials, compared to
similar R-11 and R-19 for 2×4 and 2×6 wood
frame assemblies. In addition, because the
center of the ICF walls are made with reinforced
concrete containing high thermal
mass, they typically are more energy efficient
than light-frame construction.
Achieving a high-performance building
envelope also means minimizing air leakage,
and ICF walls typically have lower air-infiltration
rates than wood frame or light-gauge
steel walls. In tests, they averaged about
half as much air infiltration as wood frame.
In many cases, the air infiltration rates are
as low as 0.5 air changes per hour. Thermal
bridging is also eliminated with ICF walls
when compared to wood and light-gauge
steel.
Noise and vibration
Noise transmission in residential buildings
is also important—to reduce noise
between units and from the outside. The
concrete core of ICF offers excellent noise
control in two ways. First, it effectively
blocks airborne sound transmission over a
wide range of frequencies. Second, concrete
effectively absorbs noise, thereby diminishing
noise intensity. Because of these attributes,
ICF walls and floors have been used
successfully in multifamily, hospitality, theater,
and school applications.
Six-inch ICF walls typically achieve
Sound Transmission Classification (STC)
rating of 55. Higher STC ratings up to STC
70 can be achieved with additional gypsum
wallboard or special isolation channels. For
ICF floors, most meet STC 50 or higher and
Impact Insulation Class (IIC) of 50 or higher,
depending on the floor and ceiling finish.
Initial Cost and Long-Term Value
ICF construction can help contain construction
costs because of the inherent
efficiencies of the installed assembly that
serves nine functions:
ORDINARY ROOFS
WASTE ME
HYDROTECH ROOFS
LEVERAGE MY
POTENTIAL
Oc t obe r 2 0 1 9 I I B E C I n t e r f a ce • 3 1
CASE STUDY: Beach Green Dunes, Rockaway, New York
This 101-unit, 94,000-sq.-ft. (8,733-m2) apartment building (Figure 14) was built in
an area devastated by Hurricane Sandy in 2012. The Bluestone Organization selected
ICFs for exterior, corridor,
and demising walls,
as well as precast hollow-
core floors for disaster
resilience and energy
efficiency. The building
is so energy efficient it is
certified by the Passive
House Institute. ICFs
create a solid concrete
wall with continuous
insulation, resulting in
a comfortable and airtight
structure that lowers
energy bills. The reinforced
concrete system
results in a structure
that is strong, durable,
and can stand up to fire,
floods, and wind. Figure 14 – Beach Green Dunes apartments. Photo © Peter
Mauss/Esto.
1. Concrete form (that stays in place)
2. Thermal barrier
3. Air barrier
4. Moisture barrier
5. Fire barrier
6. Sound barrier
7. Substrate for running utilities
8. Substrate for attaching finish materials
9. Reinforced concrete structure
In conventional construction, many of
these features are provided by several different
trades, usually at significant added
cost. ICF construction embodies all of these
characteristics in a simple assembly, usually
installed by one crew. This means the
general contractors can realize a number
of on-site efficiencies, including fewer
trades on site, reduced crew size, and an
accelerated construction schedule. Because
construction schedules are usually much
shorter with ICF construction, the general
contractor is able to finish on time and
within budget. The building owner is able to
put the building into service sooner, cutting
short his or her financing costs and initiating
a quicker revenue flow.
In general, ICF construction costs can
equal wood- or steel-frame construction.
Building with large ICF units instead of
individual, small framing elements such as
dimensioned lumber or cold-formed steel
can save on initial cost. In addition, the
lower floor-to-floor heights of ICF walls and
concrete floors (precast plank or ICF) can
3 2 • I I B E C I n t e r f a ce Oc t obe r 2 0 1 9
CASE STUDY: The Ricchi, San Antonio, Texas
The Ricchi in
San Antonio, TX,
is a contemporary
mid-rise building
consisting of
87 luxury condominiums
(Figures
15 and 16). The
developers wanted
to provide a
first-class, secure,
and quiet building
and chose ICF as
part of the plan to
achieve their goal.
Noise reduction
was a major consideration
for this project. The Ricchi is located directly below the flight path for airliners
approaching San Antonio’s international airport and is adjacent to a U.S. Army
training camp. The sound
attenuation offered by ICFs
provided a solution to those
concerns while creating significant
energy savings. The
higher insulation provided by
the ICF walls reduced HVAC
tonnage by 20 percent.
Figure 15 – The Ricchi condominiums. Image courtesy of Ricchi
Group.
Figure 16 – The Ricchi
condominiums under
construction. Image
courtesy of Fox Blocks.
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help reduce the overall height of a building,
which means additional savings from
reduced exterior and interior finishes and
reduced mechanical, electrical, and plumbing
lines, which can be significant.
CONCLUSION
ICFs represent an advancing technology.
There are thousands of examples of ICF
buildings all over the U.S., Canada, and
other parts of the world. ICFs can add value
to any type of construction project, but the
added fire safety, energy efficiency, and
noise reduction qualities make them a good
candidate for mid-rise multifamily construction.
The most common ICF brands have
similar dimensions and, thus, architects
can design a building with ICFs without
having to design it to a specific manufacturer’s
specifications. Most of the larger ICF
companies have standard specifications,
design details, and design manuals to help
architects and engineers with the design
process.
The largest ICF manufacturers have all
the necessary testing required to meet the
latest building code requirements, including
for fire, energy, sound transmission, and
structural design. In addition, because ICFs
save so much energy over time, they can
help meet LEED and other green building
standards. Although ICFs are unique in
the sense that the insulation is installed
before the structure is installed, in the end
the design details are the same as if you
installed conventionally formed concrete
bearing walls and then attached rigid insulation
to the wall.
The best way to find out about ICF
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of the National Ready Mixed Concrete
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Oc t obe r 2 0 1 9 I I B E C I n t e r f a ce • 3 3
CASE STUDY: Martin Hall and New Hall B, Eastern
Kentucky University, Richmond, Kentucky
Eastern Kentucky
University chose
ICFs for walls and
hollow-core planks
for floors for two
recent dormitories–
the 199,480-sq.-ft.
(18,532-m2) Martin
Hall and 165,580-sq.-
ft. (15,383-m2) New
Hall B. Each structure
features a recreational
room, private
and group study
areas, a community
kitchen, a large multi-purpose room, and two classrooms. The concrete floor design
allows for shallow floor-to-floor heights and ease of construction. Additionally, lower
floor-to-floor heights save on exterior finish and mechanical runs. The lateral load-resisting
system includes concrete shear walls designed to provide stability against wind
and seismic forces.
Figure 17 – Martin Hall at Eastern Kentucky University. Image
courtesy of Nudura.
Figure 18 – Martin Hall at Eastern Kentucky University under construction. Image
courtesy of Nudura.
Association (www.BuildwithStrength.com),
and with the Insulating Concrete Forms
Manufacturers Association (ICFMA) at www.
icf-ma.org.
ENDNOTES
1. ACI 318-19, Building Code
Requirements for Structural Concrete
and Commentary
2. ASTM C578-19, Standard
Specification for Rigid, Cellular
Polystyrene Thermal Insulation
3. FEMA P-361, Safe Rooms for
Tornadoes and Hurricanes:
Guidance for Community and
Residential Safe Rooms, Federal
Emergency Management Agency
4. Technical Bulletin 2, “Flood Damage-
Resistant Materials Requirements
for Buildings Located in Special
Flood Hazard Areas” in accordance
with the National Flood Insurance
Program, Federal Emergency
Management Agency
5. ANSI/UL 263, Standard for Fire
Tests of Building Construction and
Materials
6. ASTM E119-07, Standard Test
Methods for Fire Tests of Building
Construction and Materials
7. ASTM E84-19, Standard Test Method
for Surface Burning Characteristics of
Building Materials
8. ANSI/UL 723, Standard for Test for
Surface Burning Characteristics of
Building Materials
9. IECC, International Energy
Conservation Code
10. ASHRAE 90.1, Energy Standard
for Buildings Except Low-Rise
Residential Buildings
3 4 • I I B E C I n t e r f a ce Oc t obe r 2 0 1 9
Lionel Lemay is
executive VP of
structures and
sustainability for
the National Ready
Mixed Concrete
A s s o c i a t i o n
(NRMCA). He leads
a team of professionals
to offer
building owners
and designers
cost-effective,
durable, and sustainable
concrete building solutions through
education, research, and design assistance.
He has written many articles and co-authored
several books on concrete design and
construction. Lemay holds a bachelor’s and
master’s degree in civil engineering from
McGill University in Montreal, Canada.
Lionel A. Lemay,
PE, SE, LEED AP
T3 Bayside is currently under construction on the shores of Lake Ontario in Toronto’s Bayside community. The 10-story structure
will be 42 m (138 ft.) tall upon its completion – the tallest timber office building in North America. A second building of similar
size and construction is planned next to it.
Built in cross-laminated timber (CLT), the interior aesthetics will also be reflected in the exterior, with exposed timber and open
floor spaces. The structure, designed by Danish architecture firm 3XN, is planned for a LEED® Gold rating.
Plans are for it to be part of a master-planned community which will include two million square feet of luxury condos, shopping
and restaurant destinations, cultural venues, and walking promenades along the water’s edge.
Artist’s concept, courtesy of 3XN Architects.
Tallest Timber Building
in North America
Under Construction
in Toronto
SIPL