By reading, downloading or printing this online tech note, you agree to pay
the posted licensing fee in accordance with our payment terms and licensing
agreement. To keep our prices as low as possible, please note that we DO NOT
mail hardcopies. For additional information on our satisfaction guarantee
including terms and conditions, please click HERE.
Thank you for your patronage. Our authors are very grateful for your support of
Builders Websource®.
The
insulating Concrete Form, or ICF, is among the fastest growing segments of
the residential and commercial market for foundations and wall
systems. Although ICF’s represent less than 1% of the residential
market today, acceptance is accelerating. By 2005, ICF’s will represent
as much as 5% or more of the residential market, seriously
challenging traditional stick-frame wall construction. Every year
the number of homes built with ICF's doubles. Significant
performance advantages coupled with rising lumber and energy prices makes
ICF's an attractive alternative for new construction throughout North
America.
Defining ICF’s
Made of expanded polystyrene, or EPS, ICF’s are an insulating forming
system for poured-in-place concrete walls and foundations. Introduced in
Europe, ICF's have been in use around the world for over 30 years.
Over 50 manufacturers in the US and Canada make ICF’s in a variety of
shapes and sizes for use in foundations, basements, multiple-story
dwellings, and commercial facilities. Rather than using traditional
plywood or 2-by forms, lightweight ICF’s stack in a running bond pattern
forming both an exterior and interior insulated wall. Installers lay rebar
horizontally and vertically inside the ICF’s to create a structurally
sound unit designed for the expected vertical and lateral loading
conditions. After proper installation and bracing, the ICF’s are pumped
full with a soupy concrete mixture held to a 5"-6" slump.
Pre-manufactured 45- and 90-degree corners coupled with a precision
alignment system helps to adjust the walls to ensure a perfectly square
and plumb structure.
Once
the walls have cured, they form an incredibly strong monolithic structure
that is permanent and non-deteriorating. Since the protective insulation
provides an ideal curing environment, tests conducted by the Portland
Cement Association have shown that concrete is up to 50% stronger than
concrete cured in traditional wood form systems.
Types of ICF's
Typical ICF’s have inner concrete cores of 4-, 6-, and 8-inches wide.
When combined with approximately 2 to 2-1/2 inches or more of rigid foam
insulation per side, the resulting ICF wall thickness is in the 8- to
12-inch range. Finish materials such as interior gypsum wallboard or
exterior stucco or siding add another 1-1/2 inches to the total wall
thickness. Answering the demand for heavy retaining wall applications,
certain manufacturers offer systems with inner cores of 10, 12, 14 and
even 16 inches or more. Clearly these super-thick walls provide
exceptional strength, energy efficiency and sound isolation. However, the
added wall thickness also subtracts from the total available interior
floor space which, in a small or narrow home, could be significant.
Although various types of ICF's have been around for years, recent
advances and product developments are bringing an exciting new dimension
to homebuilding, virtually eliminating some of the drawbacks of earlier
systems. Evaluation of several leading products reveals fundamental
variations of the ICF core structure. While each of these variations
may influence the particular conditions under which each system is
optimum, they essentially offer similar benefits and universal strength.
ICF core structures classify into one of four types. The percentages are
based on the number of manufacturers, not the volume of each sold or
installed:
Flat System (54%)
Waffle System (10%)
Screen Grid System (29%)
Post and Beam System (8%)
Within each of the aforementioned types, there exist three typical
subtypes:
Panels (15%)
Planks (23%)
Blocks (62%)
Panels are the largest, often measuring 4 feet by 8 feet or
greater. Planks typically range from 1- to 2-feet high by 4- to
8-feet long. Finally, blocks are typically 12- to 16- inches high by
4-feet long, representing the majority of manufactured ICF's.
Regardless of the subtype (panel, plank, or block), all flat systems
have an inner core of constant width. While this system uses more
concrete than other ICF systems, it is most accommodating for rebar
placement since each cavity is wide open enabling virtually unlimited
choices in rebar placement. This is particularly important for walls
carrying unusually heavy loads or in seismic zones three or four
where it's not uncommon to see vertical rebar placement every 6" to
8", including rebar with 1" or greater diameter (#8 and
above). A leading flat block vendor in North America, for example,
is Arxx Building Products of Canada. The Arxx High-Performance Wall SystemTM
(formerly BlueMaxx) is in growing use throughout North America on a wide
range of residential, commercial, and agricultural applications. Having
seen this system on several jobsites in the San Francisco Bay Area, I
became so fascinated by this up and coming alternative construction
technique that I obtained a first-level certification in ICF installation
practices. Other vendors of the "flat" system include
Owens-Corning, Polycrete, Quad-Lock, Eco-Block, Amvic Systems, and
Formtech.
The waffle system is a variation of the flat system, resulting in a
matrix of conjoined horizontal and vertical concrete tubes. Precise
rebar placement is more critical in the grid system due to the cavity
locations, however concrete use is slightly less than comparable flat
systems. American Polysteel Forms fabricates a waffle-type unit
measuring 16 inches high by 4-feet long. Horizontal cavities are on
16-inch centers, while vertical cavities are on 12-inch centers. The
efficient waffle design results in approximately 25% less concrete by
volume per square foot of wall compared to equivalent flat form
designs. However, if your rebar spacing calls for dimensions other
than 16 inches horizontally and 12 inches vertically, your structural
engineer may have to make some adjustments to accommodate the fixed grid
spacing waffle pattern. Other popular waffle designs include,
Reward, Therm-o-Wall, and ICE Block.
The screen grid version is an extension of the grid system, except that
each vertical and horizontal member is fully isolated (except at
intersections), creating fully encapsulated concrete members. While
this system uses even less concrete than the waffle system, proper
consolidation is particularly critical. Without a proper slump, air
pockets can easily accumulate in the horizontal or vertical members,
weakening the wall system. If the mix is too wet, then the concrete
will not have sufficient final strength. Products in the screen grid
category include: Conform SWF, Faswall, and Reddi-Form.
Finally, the post and beam systems that represent the minority of ICF
types, have vertical concrete posts, with periodic horizontal
"beams" at key load points and across the top of the wall.
One such manufacturer is Amhome.
ICF's have many advantages over traditional construction materials.
Frequently cited beneficial characteristics include:
Superior strength
Inherent resistance to destructive natural forces
Excellent sound attenuation
Impervious to rot, decay, and termites
High fire resistance
Energy savings of 25-70% depending on location
Consistent indoor comfort due to high thermal mass and low
permeability
Structural longevity
Consistency in product and application
Maintenance-free
Architecturally "substantial" appearance due to thicker
walls vs. traditional 2x4 or 2x6 construction
Negligible outgassing - no use of formaldehyde during manufacturing
process
Interestingly, an overwhelming majority of ICF homeowners consistently
site comfort, noise reduction, strength, and energy efficiency as the top
four benefits realized in their new homes.
Since most people have never seen ICF’s, think of them as giant
Lego® building blocks – just like the kinds your kids play with, only
on a larger scale. Once a suitable foundation or footing has been poured,
ICF’s are stacked in staggered courses to form basements, garages, and
first and second story walls.
The Arxx system described earlier, for example, uses blocks that are
roughly 16-3/4" high by 4 feet wide. Other systems have slightly
shorter heights. In the former, six courses are required for a typical
8-foot wall resting on a slab-on-grade (SOG). Starting with square
pre-fabricated 90-degree corners, the ICF's are laid out along the
building chalk line one course at a time. As each course is laid,
horizontal rebar snaps cleanly and consistently into place, locking the
blocks together and providing ultimate tensile strength for the concrete.
Subsequent courses simply "snap" into place creating flush
joints both vertically and horizontally. No "buttering" of
joints is required as is typical of traditional concrete block walls built
with cement mortar units (CMU's).
With experience, this system is so fast and efficient that builders
erect entire structures in as little as one to two weeks, saving greatly
on field time. In addition, since the ICF's naturally have over 2" of
polystyrene insulation on either side, concrete can be poured even in
sub-freezing conditions – something difficult to do with traditional
wood forming systems.
New developments such as bullnose adjustable angled corners,
pre-fabricated 45-degree and 90-degree corners, end caps, brick ledges,
and height adjusters allow virtually unlimited flexibility,
including bay and bow windows, stepped foundations, brick and stone
veneers, and walls of arbitrary height – all cast with poured-in-place
concrete.
Integral or snap-in-place plastic or metal webs facilitates wallboard
and exterior finish attachment at as intervals as close as 8 inches,
depending on vendor. Coupled with the 4"-5" of EPS
insulation, an 8-inch core wall assembly has over an R-22 rating. However,
due to its huge thermal mass compared to a traditional wood wall, it
performs equivalent to a wooden wall assembly with an R-50 rating – if
such a thing could be built. Since the wall system is virtually
impermeable to moisture and air infiltration, no additional housewrap or
moisture barrier is required, saving yet another step in the construction
process. However, since the resulting home is very "air tight,"
proper ventilation, including air-to-air heat exchangers is absolutely
critical to ensure an ample supply of fresh exterior air and exhaustion of
stale indoor air. Without proper ventilation, unhealthy levels of
indoor air pollution will accumulate. Of course, an air exchanger is a
smart idea for any tight house, whether made from wood, steel, or ICF's.
Until you see this technique for yourself, it is difficult to describe
the sense of satisfaction one feels when stepping inside a home built with
ICF’s. Assuming double-paned windows have been installed and ample floor
and ceiling insulation exists, outside noise is virtually negated. Since
ICF's have a superior Sound Transmission Rating of 48-50 depending on the
wall thickness, typical outside noise simply cannot penetrate through the
structure to any significant degree. For this reason, many newer hotels
located next to freeways or airports are now turning to ICF’s to provide
superior sound deadening qualities while allowing their patrons to sleep
easily at night.
In
addition, since ICF's offer tremendous thermal mass, the inside
temperature of the structure remains very constant...and since there is
little to no air infiltration or exfiltration, the "draftiness"
often encountered in many homes is reduced substantially, if not
altogether. Temperature differentials from floor to ceiling are 1-2
degrees F. in ICF homes, compared to 5-10 degrees F. in traditionally
framed homes.
Unlike conventional wood construction, ICF’s when covered with
fire-rated gypsum provide a 2-4 hour firewall, which makes them an
excellent choice from a safety standpoint.
These products sound superior to other construction techniques, so what’s
the catch? Since they are "unconventional," many municipalities
and building inspectors may not be familiar with them. Out of fear or lack
of education, they may unjustly challenge their use. Furthermore, many
architects and structural engineers may not be comfortable with this
technology unless they’ve had special training or have designed
structures using ICF’s in the past. Since special certification is
required to ensure proper installation, your choice of general contractors
may also be limited to those who have installed ICF’s in the past.
In addition, manufacturer associations with competing wall forming systems
(such as wood and steel) will downplay the benefits of ICF's since they
directly compete for a finite market share. In this vein, it is
essential to understand that ICF's are not clearly superior in all
applications and, generally, a given structure will likely contain
elements of many building products, each chosen for their suitability and
cost effectiveness.
More important, however, is that certain states -- particularly where
high levels of termite infestations are common -- have banned ICF's from
underground use in basements and foundations. Unfortunately, the reasons
have little to do with the ICF’s themselves, which inherently do not
provide any attraction or nutrients for termites. Rather, termites in
search of wood products and cellulose can tunnel through the EPS
insulation to their source of food, remaining undetected. The ICF industry
is actively working to educate building departments and code writers.
However, due to this confusion, it is imperative that you consult with
your building department prior to designing a structure with sub-grade ICF’s
just in case your local code prohibits their use.
Fortunately, ICF manufacturers are working on a variety of possible
solutions to these issues, including research into alternative exterior
substances and boron impregnated polystyrene, as well as visual
"inspection" strips above grade that could help to reveal the
presence of termite tunnels.
In either case, it is imperative to follow good building practices to
mitigate possible insect infestation. Never dispose of wood or wood
by-products at the construction site or near the foundation. These will
rot over time and become a haven for termites and other insects. Consider
also whether treating the soils prior to construction is permitted as way
to discourage termites. Plus, with the increasing use and skill at using
steel framing and trusses in residential construction, the use of wood can
be all but limited to the very minimum, such as subfloor plywood, roof and
wall structural sheathing, and interior trim. Eliminating the source of
"food" is the best precaution against termites in the first
place.
Another potential issue with ICF’s, particularly in high seismic
zones, is the availability of very wide internal cavities. In California
where major faults are often within just a few miles of high density
populations, the structural aspects of cast-in-place concrete wall systems
can be impressive. As stated earlier, many home basements have vertical
rebar every 6 to12 inches, sometimes as thick as #8 or larger. Depending
on lateral and other loads, horizontal rebar may also be specified on 8 to
10-inch centers, making for a "cramped" cavity wall. Often the
concrete thickness for such walls can be 10 -12 inches – which exceeds
the interior dimensions of many of the available ICF flat block systems on
the market today. For wide walls, panel or plank systems may be
required.
However, since ICF webs can also help to ensure consistency in rebar
placement, consult with your structural engineer to see if your situation
can be handled with a 6" or 8" internal cavity thickness. Often,
simply by specifying a certain concrete strength…or adding extra rebar
can make up the required difference.
During the placement of concrete, proper attention to workmanship is
critical, since voids in the concrete are not visible from the outside and
could impact the structural integrity of the wall, lintels, and beams. For
this reason, proper concrete consolidation is essential. Sufficient
resources must be on hand when pouring. Starting from the bottom of the
form and working your way up, tap and vibrate each lift of cement to
ensure that no trapped air or voids remain inside. An orbital sander or
bladeless reciprocating saw has proven to be an effective consolidator
when used carefully on the outside of the form. It is also important to
ensure that the cement fully surrounds and "grips" the rebar to
provide embedment and tensile design strength, thus reducing premature
failure.
Use of additives are possible, such as Fibermesh. While Fibermesh isn’t
required, it can help to improve the consistency of the concrete mix…and
keep it intact as it’s poured from the top of the wall. Millions of tiny
glass strands provide localized tensile strength and shrinkage crack
control, resulting in a water-tight, crack-free structure when combined
with proper steel reinforcement. Fibermesh combined with additional steel
also helps to prevent diagonal shear cracks at window and door openings,
which tend to be weak spots in the wall. Since Fibermesh only adds a few
dollars per cubic yard to the cost of cement, it’s a small price to pay
for the peace of mind of knowing that the very best products are inside
the wall. Doing this will result in a virtually indestructible wall that
will last for many generations, if not hundreds of years or more.
Another consideration of ICF construction is the handling of electrical
wiring and plumbing. The first step is to minimize the amount of plumbing
and wiring that must be placed on typical ICF exterior walls. This can
generally be accommodated in the design process if ICF’s are assumed
from the start. However, since a certain amount of plumbing and electrical
wiring will be unavoidable, particularly in kitchens where the sink and
dishwasher often face an outside window, provisions for water supply,
waste and venting are essential. Fortunately, the EPS thickness on many
systems is as much as 2-5/8" which allows just enough room for
1-1/2" pipes (allowing for coupling diameter). Electrical wiring can
be slipped into "routed" chasteways in the EPS itself. Due to
the difficulty in changing wiring after the fact in an EPS structure,
consider using flexible or rigid conduit on these walls along with
oversized receptacle boxes. This gives you the flexibility to change the
wiring in the future such as adding a three-way switch – or another
switched lighting circuit -- since you have no way of predicting what the
needs of a particular room may be 10 or even 5 years down the road.
Conduit also protects the wire better from accidental puncture. In
addition, providing ample receptacles for telephone, cable, and future
communications connections is wise. Again, providing some metal or plastic
conduit for this purpose is smart planning and an inexpensive way to
future-proof your ICF home.
Although ICF's are extremely flexible and are limited mostly by your
imagination, there are some situations where traditional stick framing or
steel may make more sense, even if used in isolated applications in
conjunction with ICF’s. These include:
When less than 12" is required on either side of a window, such
as in a bay window arrangement
When a second story wall is not bearing down on an ICF load bearing
wall
Where arched or curved transom windows are used
Porches and popouts
Walls with minimal width which do not have adequate shear properties
(in which case steel I beam assemblies may be specified)
Gables in uninhabited attics
The notion that ICF houses look "boxy" or rectilinear is
false. Although some early simple designs did have a flat "two
dimensional" appearance, a quick look through more recent ICF home
designs quickly dispels this myth. In fact, many of the homes have
exciting and intricate architectural elements and contours reminiscent of
fine European villas, including even curved walls. To get the most out of
an ICF design, it is essential that the designer or architect is familiar
with the product and can lay out the home with an optimal design that has
both practical field installation implications as well as high curb
appeal. The best designs are those where the ICF was planned in from
the start. That way wall lengths, heights, and position of doors and
windows can be planned according to convenient form dimensions, reducing
on-site labor and cutting of forms.
Without endorsing specific products, there’s no question that you
should seriously consider and evaluate the use of ICF's for your next
home. John Wencl of Plyform and Supply, Inc. in White City, Oregon is a
field expert on ICF systems and has worked with many different systems on
the market. As a result, he offers a well grounded perspective on the pros
and cons of the major systems on the market today. He also has extensive
background in quality control and is dedicated to very high customer
satisfaction (Email: wenclpfs@internetcds.com)
Over the years, he has developed a superior knowledge of these products,
their advantages, and limitations. He is an excellent resource of
information and is a regional instructional trainer on ICF systems as
well. In addition, for those interested in obtaining on-going,
in-depth understanding of ICF's, visit the website www.icfweb.com
which has expert advice and guidance in this area. Also highly
recommended is Pieter VanderWerf's outstanding text book reference, Insulating
Concrete Forms. Pieter is a leading ICF expert and has authored
numerous books and papers on the subject.
The structural integrity, energy efficiency and comfort factor, as well
as resale value of ICF homes offers an exciting alternative to traditional
home construction. Several studies by the US government are now underway
to better understand and document the attributes of ICF construction,
including scientific energy comparisons to identical homes -- one built
with ICF's and the other built with conventional wood framing. For
reference, the following comparison chart from Building Technology
compares typical ICF performance to wood-frame construction.
(c) 1999-2001 Builders Websource. All Rights
Reserved. No portion of this application brief may be reproduced or
copied in print or electronically without written permission from the
author.
Builders Websource® is a corporate
member of ASTM International—a non-profit engineering body dedicated in
part to the standardization of building materials specifications,
products, systems, and test methods for improved health, safety, and
reliability of residential and commercial structures.
In
addition, since ICF's offer tremendous thermal mass, the inside
temperature of the structure remains very constant...and since there is
little to no air infiltration or exfiltration, the "draftiness"
often encountered in many homes is reduced substantially, if not
altogether. Temperature differentials from floor to ceiling are 1-2
degrees F. in ICF homes, compared to 5-10 degrees F. in traditionally
framed homes.