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How to Build Concrete Homes
Using Foam Forms
Tips on using one type of stay-in-place block form
BY RONALD P. ARDRES AND TIMOTHY S. FISHER
tay-in-place foam forms
have been accepted as a
quick, easy, and efficient
way to construct residential foundation walls. Now these
systems are quickly catching on as
an efficient way to construct entire
homes, from footing to eave. In
one step, the contractor can form
concrete and provide insulation
with R-values much higher than
conventional concrete walls. Other advantages of these systems
when compared to conventional
forming methods include:
• Faster wall erection (forms are
easy to erect and do not require
stripping)
• Better concrete curing and a
longer construction season (the
foam insulates the concrete)
There are two types of polystyrene foam forms: panel systems
and grid systems (see box on page
661). Each type is constructed diff e re n t l y. A grid system produces a
post-and-beam wall: a combination of many concrete columns and
beams that are spaced apart by sections of foam to resemble a large
waffle or a huge window screen.
The components of this system are
foam blocks with foam webs that
act as wall ties and filler between
the posts and beams.
The post-and-beam grid system
block has no top or bottom, making
its assembly virtually foolproof.
The system also uses less concrete
than some other systems, yet provides the same structural strength.
Many experienced contractors find
this type of system the easiest to
construct. Howe ve r, it is also a good
system for the novice builder. Following are some hints on using
post-and-beam foam block forms.
S
Planning and Design
Planning is probably the most important step in building a concrete
home. As with any other form of
building construction, a complete
set of plans is needed before construction starts. Plans that were
originally designed for lumber or
concrete block construction can
easily be altered to use concrete and
stay-in-place forms. No rm a l l y, all
that is required is to adjust the
home’s overall dimensions to a multiple of the block size. This will make
construction easier and less wasteful, since blocks will not have to be
cut to fit the original dimensions.
To get the most out of an expanded polystyrene (EPS) stay-in-place
forming system, designers should
consider the following:
• Size and location of the walls’
penetrations
• Locations of windows and doors
• Floor heights
• Floor system options
EPS systems are very flexible and
allow some unique architectural design options. Curved walls, unique
finishes, and vaulted ceilings are just
a few of the custom features that can
be included in a concrete home.
Ordering Materials
Manufacturers have quantity
takeoff formulas that can help contractors order the proper amount of
materials. If you know the squarefoot area of wall forms and some
other basic information found on
the home plans, manufacturers will
be able to give you the quantities of
materials needed, including blocks,
rebar, concrete, scaffolding and
bracing, and materials to form window and door openings.
Be sure to allow enough time for
manufacturing and delivery of the
forming system. Local distributors
often keep plenty of material in
stock, but if they’re short it can take
a while for the manufacturer to fill
your order.
Foundations and Getting Started
Width and depth of footings depend on soil-bearing capacities,
size and width of blocks, engineering designs, and local codes. Layout
and construction of footings are the
same as for conventional forming
systems. However, extra care should
be taken to place the footings flat
and level. If the footings are not level, blocks can easily be scribed and
cut, or shimmed with liquid foam
filling, but a little care when placing
concrete will save you a lot of extra
work later. Manufacturers normally
set tolerances on the levelness of
footings, so be sure to follow them.
If the home is being constructed
on a hilly site, you may need to
form stepped footings. St a y- i n place systems can accommodate
these footings in a unique way.
When forming a step in the footing
it is not necessary to form the vertical step face; just keep the height
of the step equal to a multiple of
the height of the block. For example, if the height of the block is 1
foot, make the height of your step 1
foot, 2 feet, or any other multiple of
a foot. When forming up to a step,
place a piece of steel horizontally in
the block, thus creating a grade
beam. Removing the vertical wall in
the step will reduce the amount of
time needed to form the footings.
The footings can be keyed and rebar can be pinned or cast-in-place.
With some block systems, it is easy to
locate and place rebar before pouring the footings. This is the recommended method whenever possible.
With some other block systems, it
is more difficult to locate the rebar
within the cells of the block because
of the number and size of webs
holding the block together. A small
mistake in calculations will throw
the entire layout off, and require
bending the rebar so it falls within
the cells. To prevent this problem,
drill holes in the footing and epoxy
the rebar in place when laying out
the first course of block.
After the footing is placed, the layout of the walls is marked on the footing. Along the outside of the layout
lines, nail a wood shoe into the footing. Scrap 2x4 or 5⁄4 lumber works well
as a shoe as long as it is straight. The
2x4s should be continuous around
the corners to act as a nailer for the
corner bracing. Another method is to
use a 2-inch, 25-gauge U-channel.
Simply fasten the U-channel on the
building line using nails for concrete,
and insert the block into the U-channel. This will prevent the block from
moving off the building lines in any
direction.
Placing Blocks
The first course of block must be
level. The forms should be erected
following the manufacturer’s instructions, as each system is different. Start from the corners and work
t ow a rd the middle by placing any
cut pieces in the middle of the wall,
much like installing concrete block.
Use a 4-foot level to check the block
as you pro g re s s. After setting the
first course, start on the second
course by staggering the joints.
Staggered joints strengthen the wall
and help keep it aligned. The first
couple of courses are called layout
courses and are important steps for
a straight and true wall.
Wall forms should be built and
concrete placed one story at a time.
When the wall begins to reach onestory height, place a piece of vertical
steel that is long enough to lap splice
to the next story’s reinforcement. If
you are going to continue upward
with subsequent pours, be sure to
cover the interlocking teeth of
the block to keep
them free of concrete.
Below-grade
walls normally require much more
reinforcement
than above-grade
walls. Some systems have ties
that act as chairs
to hold horizontal
bars, and others
have
special
chairs. Since wall
construction
moves rapidly, be
sure not to get
carried
away:
Don’t forget to
place bars where
needed.
Tie the ve rt i c a l
bars to the dowels
in the footing. Af- Window bucks should be installed before concrete
ter vertical bars placement. Additional bracing is required on the inside of
are in place, it is large openings to keep the openings square and true.
necessary to slide Concrete has already been placed in this wall.
the blocks down
over the bars. If
tems have corner blocks that can be
the bars are cut short, you can
used instead. In all the systems, anreach over them easily. Howe ve r,
gles other than 90 degrees are creatthis will require a lot of bar splicing
ed by mitering, gluing, and taping
and will quickly eat up your reinblock together. These angles should
forcement budget. To use longer
be braced for plumb before you
bars, you must devise a system to
pour the concrete. Most systems
get the blocks up and over the bars.
can be bent or cut in such a way as
One contractor has devised a tool
to create a curved wall of almost any
that consists of a 1x3 with a nail
radius over 4 feet. To accomplish
d ri ven through one end. When
this, cut pieces of foam out of the
placing blocks, he simply stabs the
back side of each void. The manublock with the nail and uses this to
facturer can supply a chart or forhoist the block up over the bar. One
mula that tells you how big the cut
manufacturer offers a tie with a
must be for a given radius. Curves
hole in the center for use with its
can also be created by sculpting the
system. A few of these ties are
foam with a hot-wire cutter or rasp,
placed in the wall at different
or by gluing pieces of molded foam
heights wherever vertical reinforceto the side of the foam wall.
ment is needed. When the wall
Doors and Windows
forming is done, vertical bars are
slid into the holes in the ties, alignOpenings of any kind are easily
ing them in the center of the block.
achieved with polystyrene systems.
With some block systems, corConstruct a frame to box out your
ners must be created by mitering
desired rough opening using a presand then gluing and taping block
s u re - t reated 2 x10 or 3⁄4-inch prestogether with duct tape. Other syssure-treated plywood. Build a three-
sided form, two legs and a head, to
the desired rough opening using
the 2x10s or the plywood. Make the
bottom of the three-sided form using two 2x4s, leaving a gap in the
middle. The gap allows you to pour
below the opening and visually
check that the area below the opening is filled properly. You should insert the wooden frame as soon as
possible and continue to install the
block around the frame. Once you
have completed the wall, add 1⁄2inch bolts or galvanized spikes
through the window frame, and
then add a frame of 1x3s around the
outer edges of both sides to help
support and keep the frame centered in the wall. On larger openings, extra bracing may be needed.
Each manufacturer should supply a
lintel chart with its product (Figure
1). Be sure to consult this chart for
the size and length of reinforcement
needed over an opening.
Windows can also be installed before pouring the concrete in the walls.
To do this, build the frame as described above, wrap the window in
plastic to protect it from concrete
splatter, and install it. After placing the
concrete in the wall, remove the plastic. Doors can be installed similarly.
Bracing
Start bracing at wall corners by
nailing together two 2x4s to form a
corner and then bracing it back to
the footing. This will plumb the
wall in both directions simultaneously (Figure 2). Metal studs also
can be used for bracing following
the same procedure. If you are going to reuse the bracing, metal corner posts and bracing are much
more durable and tend to be
straighter than lumber.
Additionally, the walls should be
braced every 10 to 20 feet with vertical members supported by a kicker securely fastened to the ground
or floor. In most cases, you can fasten intermediate bracing to the
plastic or metal ties; in cases where
this is not possible, a 9-inch shorttail snap tie and hairpins work well.
Another method is to use some
threaded rod with nuts and washers. If it is below grade, the kicker
can be placed horizontally and
used to support scaffolding from
which pouring can be done. Elevated walls for the second story should
be braced from the interior. After
floor decking is installed, run
braces from the floor to the wall for
support. These are minimum bracing requirements and should be
adjusted as conditions require.
Bracing must be adequate to safely
support the wall under all conditions, especially high winds.
Scaffold the entire wall system prior to pouring. Several manufacturers
offer a bracing/scaffolding system,
which can save a lot of time in the
long run. If these systems are not
available, it is very simple to construct a bracing/scaffolding system
using lumber, pipe, and turnbuckles.
The turnbuckles allow the wall to be
TYPES OF EPS FOAM FORMS
There are several stay-in-place foam forming systems for concrete construction on the market today. Expanded polystyrene is a plastic foam made of polystyrene filled with tiny gas bubbles; extruded polystyrene is a seamless foam made by extruding EPS continuously through a die. There are two types of
forms and three basic EPS formats:
Panel System
Grid Systems:
Blocks with
metal or plastic
ties
Blocks with
foam webs
Description
R-value
Cost
This type consists of off-the-shelf
sheets of foam held together
by plastic ties. Panels are made
of two sheets of foam that are
normally 2 inches thick, totaling
4 inches of insulation.
Ranges from
20 to 21.5
Ranges from $1.80
to $2.50 per
square foot
These systems are known as
“insertion-molded.” They are
shipped to the jobsite with the
metal or plastic ties fused into
the foam block. These blocks
form a cavity into which the
the concrete is poured.
Depending on
the system,
ranges from
20 to 30
Ranges from
$2.00 to $3.00
per square foot
This system creates a true postand-beam system, reducing the
amount of concrete needed
to fill the form. The foam webs
add rigidity to the blocks.
Ranges from
20 to 30
Ranges from $1.50
to $2.50 per
square foot
Source: The Portland Cement Association’s Guide To Concrete Homebuilding Systems, published by The McGraw-Hill Companies, 1995.
plumbed easily. If job conditions are
right, rolling scaffolds work well.
When placing concrete from the inside of the wall, set rolling scaffolds
on the deck and roll them around
the bracing to wherever needed.
Floor-to-wall Connections
Where continuing up with the
form for additional stories, attach a
ledger directly to the form to support the floor. Before affixing the
ledger board, drill holes approximately 5 inches in diameter in the
foam to correspond to the center of
every cell. Do not bolt the ledger directly to the foam, since it will compress after you tighten the bolts. Also, a bolt sticking through the foam
is not supported and can bend under the weight of the floor. It is best
to stagger the holes rather than
place them in a straight line.
Predrill holes in the ledger corresponding to the holes cut in the
foam and set anchor bolts so they
fill the core. Support the ledger in
place, and when the concrete is
poured, it will flow against the
ledger, firmly embedding the anchor bolt. Manufacturers also supply details for attaching other types
of floor systems. Precast slabs,
open-web steel joists, and fire-cut
joists are a few other forms of decking that can be attached to the stayin-place concrete wall system.
Placing Concrete
After the wall is completely erected and all openings are in place,
check that the wall is plumb, level,
and square. Make any necessary adjustments at this point before placing concrete. When you are ready to
pour concrete, any desired placement method can be used. A pump
is often the recommended method,
since it is the easiest and least timeconsuming. Howe ve r, concrete can
be placed by bucket, shovel, or directly from the chute of the truck.
When pumping, a hose of 2 or
21⁄2 inches in diameter works best.
Use of a larger hose cuts mobility
and productivity, unless the hose
is controlled or suspended from a
boom. If a boom pump is used,
c a refully monitor the pump ra t e
and use an elbow near the end of
the hose to help reduce the force
of the falling concre t e. When
placing from the chute of the
truck, it is often helpful to build a
trough to funnel the concrete into
the wall. This will cut down on
spilled concrete.
Always start the pour thro u g h
the slots in the window frame. Allow concrete enough time to set so
you can continue the pour upward
and not have concrete spill out
f rom beneath the window. After
this is done, start at the corn e r s
and work your way around the
wall. Be sure to fill both sides of
door and window openings evenly
to prevent movement of the wooden frames and to equalize the
p re s s u re of the concre t e. Do not
allow the concrete to drop or create a plopping action in the form;
instead, let it flow into the form
( Fi g u re 2). A plopping action increases pressures upward and outward on the forms and will cause
floating in some systems. Each
m a n u f a c t u rer has a suggested
concrete mix design and pouring
rate. Lift heights range from 4 to 10
feet, depending on the manufacturer’s recommendations. It is very
i m p o rtant that you follow these
recommendations in all cases.
Figure 1
OPENINGS AND HEADER CONSTRUCTION
For most systems, slumps of 4 to
6 inches work best, and 5 inches is
the optimum. Also, pea-gra ve l
mixes work best, since the forms
usually are only 6 inches wide, and
with the rebar and ties, space tends
to be very tight. The pea-gravel mix
will flow much better than larger
aggregates around the steel and
through the voids, and it will aid in
consolidation. When consolidation of concrete becomes necessary, a large flat-plate orbital
sander applied to the exterior of
the form works well. Or, a concrete
vibrator placed on top of the vertical steel will vibrate the steel, and
in turn, consolidate the concrete. It
is difficult to vibrate within the
form, since most of the systems are
6 inches wide, and with the addition of steel, it becomes almost im-
possible to insert most vibrators
into the concrete.
Blowouts. If forms are handled
properly, blowouts should not occur. If there is a blowout, the wall
will stay intact, but an opening will
be created that can easily be fixed.
First, remove the piece of wall that
has blown out, clean the spilled
concrete around the area, and replace the blown-out piece. Us e
two pieces of lumber secure d
through the wall by lengths of tie
wire, snap ties, or threaded rod to
keep the patch in place. Re p o u r
the blown-out area, and re m ove
the lumber after the concrete has
set. If the tie system is stuck
through a foam web, it can be removed easily and used again. It is
helpful to keep a premade blowout
kit on hand in case of a failure.
Figure 2
BRACING DETAILS AND CONCRETE PLACEMENT
Attaching Sills
Attaching floors or roofs to the
wall system is quite simple. The
possibilities are many, and the one
you select will depend upon your
particular building method. When
using these systems for foundation
walls only, save a lot of work by cutting, drilling, and installing foundation bolts in your sill plates. Simply
set them in the wet concrete after
pouring, and tap the top of the bolts
or the sill to consolidate the concrete around them. The next day,
simply tighten the bolts. By doing
this, you will create a sill seal because the concrete will have shrunk
slightly, and as you tighten the bolts
they will compress the foam into
the sill, creating the seal. A sill plate
is also placed on top of the wall for
the attachment of trusses or conventional framing for the
roof.
Utilities
Place piping with a diameter greater than 3
inches prior to the concrete pour, or use a sleeve
to block out a hole for
pipe insertion. Piping
with a diameter of 3 inches or less can be installed
by drilling through the
f o rm web after the pour
has been completed. For
interior piping with a diameter greater than 2
i n c h e s, place the piping
in the forms before pouring concrete. After pouring, electrical conduit
and plumbing is easily installed in the walls with
the use of a hot-wire cutter or router and some
common hand tools.
First, locate all box and
f i x t u re locations. Box e s
can be attached with adhesive to the foam or with
p ower fasteners to the
c o n c rete wall after the
foam has been cut away.
After the boxes are in
p l a c e, a small channel
can be cut into the foam
with the hot-wire cutter or router.
The wires or pipes are then located
in the channels and inserted into
the boxes or fixtures.
Wall Finishes
For below-grade walls, it is recommended that a fully adhere d
waterproofing membrane system
be used. For above-grade exterior
walls, a finish must be applied to
protect the foam from ultraviolet
light. A multitude of options is
a va i l a b l e. If using any methods or
p roducts that you are unsure of,
test them in an inconspicuous
area or on an extra form. This will
g i ve you a chance to check for
qualities such as color and bond,
and the compatibility of the finish
material with the foam. Some materials are volatile and can destroy
the foam, especially petro l e u m based coatings. Test all materials
that you are unsure of on a piece
of scrap foam and observe it over
s e ve ral days. Most systems offer
attachment stri p s, usually made
of metal or plastic. These stri p s,
which run in a pattern on the
block, allow you to dri ve nails or
s c rews into the block to attach
finish materials.
E x t e rior finishes. Ex t e rior finishes range from brick or stone
veneers to any type of wood, plastic, or aluminum siding. So m e
f o rm manufacturers have designed brick shelf blocks to support brick or stone veneer. Others
p rovide instructions on how to
c reate a brick shelf. Once the
shelves are in place, use a waterproofing membrane to at least 18
inches above grade and wrap the
shelf. This will take care of any
weeping through the brick and
the stone. Be sure to provide weep
holes for condensation in the bottom of the brick or stone veneers.
Then simply finish the veneer as
you normally would. Brick ties
can be fastened to some of the
systems using their plastic or
metal ties. Other systems have to
be cut so the brick ties are attached to the concrete.
Stuccos of all types work very
well with these forming systems.
When using thin-coat systems, you
can add foam moldings or any
foam design that can be cove re d
with the stucco. Most of the thincoat manufacturers have information on how to apply these moldings and designs. Hard-coat stucco
systems can also be applied using
a self-furring chicken wire or masons’ lathe attached to the plastic
or metal ties or fastened directly into the concrete. Bonding to the
foam is enhanced by the addition
of a latex modifier in the base
course, or scratch coat.
Wood, aluminum, or vinyl siding
can be fastened quite easily. I recommend installing a wood or metal
lathe prior to the siding installation
using a combination of mechanical
fastening and glue. Using the lathe
accomplishes two functions:
• It creates an air space, which
will increase the R-value, and
permit air to circulate and the
wood to breathe. This prevents
a buildup of moisture when any
type of wood siding is used.
• In the case of aluminum or vinyl
siding, it allows it to expand and
contract freely without rubbing
the foam.
Interior finishes. Sheetrock is
applied using a combination of
glue and some type of mechanical
fastener. The least amount of mechanical fastening is best. It cuts
down on spackling and creates a
better finished job, since foam
shrinks very little. To add moldings,
base crowns, and chair rails, attach
a strip of thin plastic, light-gauge
steel, or aluminum prior to attaching sheetrock to provide a sufficient
nailing base for the moldings. Also,
many types of foam moldings can
simply be glued on. By code, a 15minute thermal barrier must be applied to all interior living spaces.
This can be accomplished with 1⁄2inch-thick sheetrock.
Ron Ardres is president of ReddiForm Inc., an Oakland, N.J., company
that manufactures EPS forming systems. He is also president of the Insulating Concrete Form Association.
PUBLICATION # C950659
Copyright © 1995, The AberdeenGroup,
All rights reserved