With the economy struggling in recent years, architects, designers
and contractors have continually searched for ways to make pool
construction more economical. Subsequently, projects have realized
cost savings by utilizing innovative and efficient construction
means and materials. Geofoam has been one such solution.
WHAT IS GEOFOAM?
Geofoam is a rigid, engineered, lightweight fill material made up
of expanded polystyrene (EPS) or “foam”. Geofoam is
approximately 1 to 2 percent the weight of soil and 10 percent the
weight of water. Yet, geofoam maintains a compressive strength
suitable for many structural applications making it an attractive
fill material. Although geofoam can be manufactured in many sizes
and shapes, a standard block is typically 4 feet wide by 8 feet
long. Once on site, geofoam can be easily trimmed to the required
size by using a hot wire cutter, hand saw, or chain saw. Due to the
low density of geofoam, the blocks can be maneuvered by hand or
placed with small mechanical equipment. Geofoam is typically placed
on level ground with the first course sitting on 2 inches of sand.
When placed, the blocks are staggered so their joints are not
located on the same vertical plane, similar to kids’ building
blocks. To prevent shifting, the blocks are interconnected with
either barbed gripper plates or an approved adhesive. Recent costs
estimates of geofoam vary from $50 to $100 per cubic yard depending
on the required density needed.
Retaining/Pool Walls — The design and
construction of pool walls are generally driven by the lateral
pressure from soil backfill. The amount of pressure placed on the
walls is directly proportional to the weight of the backfill
material. As a result, lateral pressures on a pool wall can nearly
be eliminated by replacing the soils within the
“active” zone behind the wall with geofoam. This can be
accomplished by laying back the native soil or backfill to its
natural angle of repose. The angle of repose is the maximum slope
at which loose, solid material will remain in place without
sliding. The resulting wedge shaped void behind the wall is then
backfilled with geofoam. Similarly, the use of geofoam as backfill
nearly eliminates the lateral earth pressures on a wall generated
from a seismic event. By reducing the lateral pressures on a wall,
designers can specify lower structural requirements for the wall
and foundation leading to significant cost savings on materials and
Rooftop Landscaping — Green roofs for
mechanical rooms and cabanas have become more desirable in recent
years and are found on a large percentage of new construction
projects. Some projects include rooftop planters while other roofs
are covered with several feet of soil for extensive planting.
Regardless of the design, geofoam can replace traditional soil or
gravel backfill above the roof significantly reducing vertical dead
loads thus allowing the designer to minimize the structural
requirements of the roof and supporting foundations. The ease of
block placement over rooftops also makes geofoam more attractive
than the alternatives. Sufficient planting soil can still be placed
around the geofoam to maintain desired landscaping. Placing geofoam
over rooftops also provides an added insulating benefit.
Insulation — As energy costs continue to
soar, it is becoming more and more expensive to heat swimming pools
and maintain spa temperatures. One of five ways that pools lose
heat is through conductance to the soil surrounding the shell. One
method that can help minimize this type of energy loss is to
insulate the pool with geofoam. Given that it is approximately 98
percent air by volume, geofoam is a very efficient insulator.
Significant energy savings are achievable simply by lining the
pool/spa excavation with 2 to 3 inches of geofoam prior to
Compressibility — Swimming pools are
sometimes constructed in multi-story buildings or over below-grade
basements or parking garages. In this instance the pool is
constructed within a concrete vault designed by the building
structural engineer. It is common for the vault supporting the pool
to sag and deflect over time. Since a pool shell is a relatively
rigid structure, it is prone to cracking if such deflections are
experienced. A cracked pool leaking water where habitable space is
located below is not a very desirable situation. As an option to
help reduce the potential for damage caused by vault deflection,
geofoam can be placed between the floor of the concrete vault and
the floor of the pool. As the underlying vault floor sags and
deflects, the geofoam compresses and re-distributes the loading
from the pool and reduces the amount of deflection the pool
actually sees. Geofoam is available in a wide selection of
compressible resistances that can be selected based on the
anticipated load and deflection.
Waterfeatures/Slides — Large waterfeatures
and waterslides are constructed in conjunction with swimming pools
on a regular basis. Waterfeatures are traditionally constructed
using various methods such as solid sculpted concrete, stacked
natural rock, and glass-fiber reinforced concrete (GFRC) panels.
All of these options require large amounts of material that have
considerable weight. When constructed adjacent to a swimming pool,
these features can place large loads on the pool shell.
Subsequently, the pool shell has to be strengthened in order to
support the additional surcharge loads. As an alternative to
traditional construction, the majority of the feature could be made
Once the geofoam is stacked into the desired configuration, a thin
structural shell can be shot directly over it (no forms necessary)
and can be sculpted into rock or shaped for natural rock placement.
Water features constructed in this manner weigh only a fraction of
those created with traditional methods and significantly reduce
surcharge loads imposed on adjacent pool walls. Similarly, geofoam
can be stacked along the underside of a proposed waterslide.
Shotcrete can then be shot over the geofoam and formed into your
desired waterslide size. The geofoam acts as a permanent interior
form and reduces surcharge loads on the pool shell due to the
weight of the completed slide.
The use of geofoam on a project is only limited to one’s
imagination and creativity. The unique properties of geofoam allow
impossible projects to be possible. For example a recent pool was
designed as a 6-foot-deep vessel with a 6-foot-tall raised bond
beam. The raised bond beam retained a flat backfill that had
natural landscaping. Several months after the pool was completed,
the owner decided that he wanted to construct a 5-foot-tall
retaining wall immediately behind and above the raised bond beam to
create an elevated lawn area.
The problem was the raised bond beam and pool wall were not
designed to support the additional surcharge from the retaining
wall and additional 5 feet of soil. The owner’s request would
have been impossible had it not been for the innovative use of
geofoam. In lieu of placing an additional 5 feet of soil behind the
proposed retaining wall, 5 feet of geofoam was placed instead. By
using geofoam, nearly all potential surcharge loads from the fill
were eliminated, making the project a reality. Moreover, the
structural requirements of the retaining wall were minimized and
the fill was able to be placed by hand without the use of
mechanical equipment as the original pool construction cut off easy
access to the site.
ADVANTAGES OF GEOFOAM
Using geofoam as an alternative to traditional soil fill or forms
of construction has many benefits that lead to overall project cost
savings. The following are some of the added benefits of utilizing
- Shotcrete, gunite, or soil can be placed directly against
geofoam eliminating the need for expensive forming.
- Construction traffic and import costs are minimized as 1
flat-bed truck of geofoam is equivalent to 12 to 13 dump truck
loads of traditional fill. Congestion on the roads leading in and
out of a project site is minimized.
- The construction time of a project is reduced as several
feet of geofoam can be placed in a fraction of the time that it
would take to place and compact traditional soil fill in the
required 8- to 12-inch lifts. As an added incentive, geofoam does
not require compaction testing like traditional fill.
- Tight construction scheduling can easily be maintained
using geofoam as it can be installed during any type of weather or
- The lightweight nature of geofoam allows it to be
maneuvered by hand and used on projects with tight construction
access where the use of larger mechanical equipment may not be
- Geofoam is eco-friendly. It can be recycled and reused in
many additional manufacturing processes.
As with any construction material, there are also special design
considerations that must be acknowledged where geofoam is used in
design:Geofoam is subject to damage when exposed to certain
hydrocarbon chemicals or solvents. The presence of these items
should be considered during construction and if needed, the geofoam
can be blanketed with hydrocarbon resistant geomembranes for
protection.Although geofoam is treated with fire retardant, the EPS
used to manufacture geofoam is combustible. Care should be taken
when construction around geofoam includes open flames.Geofoam exposed to sunlight for extended periods of time is
susceptible to degradation from ultra-violet light although the
degradation does not tend to hinder the product’s integrity.
Surficial discoloration generally occurs but can be removed by
washing or grinding.Given the lightweight nature of the geofoam blocks, care
should be taken when stockpiling the material on job sites where
windy conditions exist. The block stockpiles can be weighted or
tied down as necessary.