Insulating Concrete Forms
Insulating concrete forms result in cast-in-place concrete walls
that are sandwiched between two layers of insulation material. These
systems are strong and energy efficient. Common applications for
this method of construction are low-rise buildings, with property
uses ranging from residential to commercial to industrial. Traditional
finishes are applied to interior and exterior faces, so the buildings
look similar to typical construction, although the walls are usually
|End view of typical preassembled flat wall
Overview and History
Insulating concrete forms, or ICFs, are forms used to hold fresh
concrete that remain in place permanently to provide insulation
for the structure they enclose. Their history dates back to the
period after World War II, when blocks of treated wood fibers held
together by cement were used in Switzerland. In the 1940s and 1950s,
chemical companies developed plastic foams, which by the 1960s allowed
a Canadian inventor to develop a foam block that resembles today’s
typical ICFs. Europeans were developing similar products around
the same time.
In the 1980s and 1990s, some American companies got involved in
the technology, manufacturing blocks and panels or planks. By the
mid-1990s, the Insulating Concrete Form Association (ICFA) was founded
to do research and promotion of the products, working toward building
code acceptance. They also worked with PCA to build awareness of
this type of construction. Although there were some obstacles—costs
could be greater than frame construction because people didn’t
understand the system, builders had to work closely to get code
approval, and materials were proprietary—the number of ICF
form producers grew. As a result, competition increased and costs
The new companies developed variations and innovations to distinguish
one system from another. Over time, some ICF manufacturers consolidated,
leading to a smaller number of larger companies. Because ICF systems
offered performance benefits like strength and energy efficiency
and were initially more expensive to construct, the first target
market was high end home construction. Custom home clients were
willing and able to pay extra for the premium quality. As word of
ICFs grew and innovations reduced manufacturing and installation
costs, builders began using the forms for mid-price-range homes;
some production builders now create entire large developments using
In the past, single family residential accounted for about 70% of
ICF construction—versus about 30% for commercial or multifamily
uses—but the products are suitable for all these applications,
and larger buildings appear to be a growing market for ICFs. They
have become popular for a variety of commercial projects including
apartments or condos, hotel/motel, retail, and even movie theaters.
foot tall ICF walls for multi-screen theatre project in Utah.
ICFs provide benefits to builders and building owners alike.
- strong walls
- disaster resistance and safety
- mold, rot, mildew, and insect resistance (below grade can require
- sound-blocking ability
- overall comfort
- energy efficiency and resultant cost savings
Contractors and builders like:
- fast, easy construction
- light weight for easy shipping and erection
- compatibility with carpenter trades
- ability to meet higher energy code mandates with less complicated
Sizes, Components, Configurations,
systems can vary in their design. "Flat" systems yield
a continuous thickness of concrete, like a conventionally poured
wall. The wall produced by "grid" systems has a waffle
pattern where the concrete is thicker at some points than others.
"Post and beam" systems have just that – discrete
horizontal and vertical columns of concrete that are completely
encapsulated in foam insulation. Whatever their differences, all
major ICF systems are engineer-designed, code-accepted, and field-proven.
The two insulating faces are separated by some type of connector
or web. Large preassembled blocks stack quickly on site. Panels
or planks ship more compactly, but must be assembled into formwork
on the job. Foam is most often EPS, expanded polystyrene. It can
be XPS, extruded polystyrene, which is stronger, but also more costly.
A few products are made with recycled foam or wood fiber in a nod
to green construction. The salvaged material is formed into blocks
with cement, making units ideal for direct application of plaster
The ties that interconnect the two layers of insulated forming material
can be plastic, metal, or additional projections of the insulation.
There are advantages to each type of material, but one current trend
incorporates hinges into the ties that allow preassembled forms
to fold flat for easy, less costly shipping.
The joints between individual forms can feature interlocking teeth
or a tongue and groove configuration molded into the forming material,
or simple butt jointed seams. Many manufacturers have developed
units with universal interlocks that allow the forms to stack whether
the form is flipped one way or the other. These “reversible”
forms save time during placement and prevent improper alignment.
Special units for corners, floors, and roof assemblies round out
the product lines and improve the engineering of the system and
energy efficiency of the final construction.
|Stacking preassembled ICF formwork
||Example of preassembled corner blocks
Block sizes are typically on the order of 16 in. high by 48 in.
long. The cavities are commonly 6 or 8 in. wide but can be larger
or smaller as needed. The foam faces are also capable of being varied,
but 1-7/8 in. to 2-3/4 in. thickness is a usual range. So an 8-in.
cavity with a 2-in. foam face on either side would lead to a 12-in.
formed wall. More recently some systems have developed the capability
of offering thicker layers of foam to enhance performance.
After finishes are applied inside and out, typical final wall thickness
is greater than 1 ft. This means that the depth of window and door
surrounds have to be wider than what is used for traditional frame
construction, with resulting deep window sills—a nice feature
for homeowners or other building occupants.
ICF systems are installed in a manner similar to masonry. Builders
usually start at the corners and place a layer at a time to build
up the wall. Some units, particularly those that form a “waffle”
or post–and–beam concrete wall profile must be glued
together or taped at the joints during assembly. Most systems today
feature uniform cavities that improve flowability of the concrete,
reduce the need for adhesives during stacking, resulting in flat
concrete walls of consistent thickness.
|Waffle grid ICF block creates variable concrete
|Placement of concrete in ICFs with pump
Once the forms are in place and braced and required reinforcement
installed, concrete is pumped into the forms. Even with the bracing,
forms need to be filled at an appropriate rate based on formwork
manufacturer recommendation to prevent misalignment and blowouts.
Product advancements and improved construction techniques have greatly
reduced the potential for form failure. It seldom occurs when manufacturer
recommendations are followed. Reinforcement in both directions maintains
the wall strength. Openings for doors and windows require bucks
to surround the opening, contain the fresh concrete during placement,
and provide suitable material for fastening windowor door frames.
Block-outs are needed when bearing pockets are required for floor
or roof items. ICF systems are compatible with concrete floors,
and wood or steel floor joists. In smaller buildings, ledger assemblies
for floor framing attachment mounted to the side of the formwork
are common. In larger buildings or those for commercial uses, steel
weld plates or bolt plates can be preinstalled within the formwork
so they become embedded in the fresh concrete.
|Embedded weld plates for structural
Finishes are usually attached via the flat ends of metal or plastic
ties embedded in the forming material. Finishes can alternately be
furred out with furring strips. Almost any type of finish can be used
with these systems. Wallboard remains the most common interior finish
and is the most typical means of meeting the code requirement for
a 15-minute fire barrier over plastic foams surrounding living spaces.
Exteriors are much more varied and depend on customer preference.
Cement plasters are applied over ICFs in a manner similar to other
|Utilities are typically recessed into cutouts
in foam after concrete has been placed
A major appeal of ICFs is the potential for
reducing energy to heat and cool the building. Some estimates
place the savings at 20% or more. The R-value for a typical ICF
is about 20. The walls can often have high air tightness—10%
to 30% better than frame-with compatible windows, doors, and roof.
As a result, assuming a 100-year service life, one single-family
ICF home has the potential to save about 110 tons of CO2
compared to a traditional wood frame home. This more than offsets
the CO2 associated with the production of the cement
used to make the concrete. See graph below.
Thermal mass is one of the reasons that ICFs work so well to maintain
a consistent temperature; insulation is the other. As the graph
above demonstrates, this saves quite a bit of energy associated
with heating and cooling, which not only saves money, but also provides
a more comfortable interior.
ICFs save trees because the wood frame is eliminated. ICF systems
can also contain a decent amount of recycled materials. Concrete
can be made using supplementary cementing materials like fly ash
or slag to replace a portion of the cement. Aggregate can be recycled
(crushed concrete) to reduce the need for virgin aggregate. Most
steel for reinforcement is recycled. Some polystyrenes are recycled.
From a sustainability viewpoint, the reduced operating energy, reduction
of CO2, long service life, and use of local and recycled
materials make ICF construction environmentally beneficial.
When ICFs were first introduced to North America, codes officials
were not familiar with the system, so there was a learning curve
associated with approval. As reinforced concrete walls, ICFs are
quite strong. But they are built in an entirely different manner
than wood frame walls and require different evaluation criteria.
Many form manufacturers performed testing and prepared Evaluation
Service Reports or something equivalent to that as a way to demonstrate
the wall system’s integrity. Groups that generate these reports
include the International
Code Council Evaluation Service, Inc. and the Canadian
Construction Materials Centre.
As insulating concrete forms have increased in popularity, code
approval has become much simpler. For one and two family dwellings,
the International Residential Code (IRC) addresses foundations and
below grade walls in Section R404 and above grade walls in R611
for homes up to two stories plus a basement. For larger buildings
like multi-family and commercial structures, an engineer is typically
required for structural design and an Evaluation Service Report
documenting approval of the ICF for the type of construction mandated
for the project will often be needed to finalize approval.
Concrete Form Association (ICFA) is a trade group of ICF manufacturers
and others related to building with ICFs.
Related Resources on Insulating Concrete
100-2007, Prescriptive Design of Exterior Concrete Walls for
One- and Two-Family Dwellings This publication
explains the prescriptive design standard for exterior concrete
walls for one- and two-family dwellings. The new consensus standard
applies to the design and construction of concrete footings,
foundation walls, and above-grade concrete walls built with
insulating concrete forms or removable formwork.
Mass Comparison of Wall Systems Due to the thermal
mass of concrete, houses with concrete structural walls typically
have lower heating and cooling costs than homes with conventional
wall systems. This CD includes a report on the thermal performance
of 11 different structural wall systems in various climates
throughout the U.S. and Canada.
Sizing for Concrete Homes
PCA’s popular software program for sizing the heating,
ventilating, and air conditioning systems for concrete homes
has been updated to the latest codes and standards. The software
calculates the system capacities based on the house dimensions,
construction materials, infiltration, location (U.S., Canada,
and Mexico) and thermostat set point. The user has the capability
to model a two story house with separate heating or cooling
systems on each floor.
Concrete Forms Construction: Demand, Evaluation & Technical
Practice Written by acclaimed
ICF industry expert Dr. Pieter VanderWerf, this guidebook walks
contractors through the business and technical aspects to consider
when adopting ICFs. Applicable for ICF construction in both
residential and commercial markets.
Concrete House: Building Solid, Safe and Efficient with Insulating
This book guides the homebuyer through the construction process
of an ICF home. Written in a question-and-answer format, this
hardback book covers all the phases of purchasing, planning
and building. It also discusses the pros and cons of ICF homes.
Written by Pieter A. VanderWerf, a top expert in the concrete
Sustainable Dream Home
career demands of a young married couple dictated finding a suitable
city residence, one that had plenty of space and was located close
to downtown Chicago. With a shorter commute, the parents would be
able to spend more family time with their two children. Knowing
that they planned to live there for at least 15 to 20 years, the
owners recognized early in the process that they wanted the home
to have energy efficiency, quality, and permanence. They determined
insulating concrete form (ICF) walls provided the best performance
for their needs. More
about the ICF home.
Converting to Concrete Keeps Residents
Safe and Warm
may seem obvious, but if you start construction in Wisconsin in
October, the weather is likely to pose a challenge. Such was the
case for the Sauk County Health Care Center (SCHCC), a single-story
assisted living facility located in Reedsburg, Wis., 50 miles north
of Madison. Yet even before ground broke or the temperature started
dropping, ICFs gained favor with the Sauk County Board: facility
supervisors felt strongly that providing a fire-safe, disaster-resistant
building was the most important thing they could do to assure the
well-being of their residents. More
on the SCHCC.