Even in prolonged, damp conditions, EPS works well as below-grade insulation. A Minnesota study of 7-year-old EPS foundation insulation found moisture levels of only 0.13%, equivalent to retaining 95% to 97% of its thermal efficiency.

Over the past few years, there has been growing interest in how ICF technology deals with moisture. The structural concrete core of an ICF wall is, of course, unaffected by water. But it’s a concern because if moisture and excess humidity penetrate the building envelope, it creates the potential for mold, mildew, and rot in other building components, such as drywall and wood framing.

To combat this, reputable ICF installers and architects use proven techniques to minimize the possibility of water infiltration. Thousands—probably hundreds of thousands—of ICF buildings have been built over the past decade with zero moisture problems. Regrettably, there have also been a small handful of projects with inadequate designs, and advocates of other building systems have tried to pin these failures on an underlying flaw in ICFs themselves.

The fact is, ICFs are one of the best construction choices for areas prone to moisture concerns. This has been proven in the laboratory and the real world.

One recent example of an attempt to tie ICFs to moisture problems is the current marketing campaign by Dow Chemical Co. The company makes an extruded polystyrene board (XPS) that competes against traditional EPS. The EPS Industry Alliance says Dow makes “unsupported claims about XPS’ superior water resistance” and the “long-term performance for XPS and EPS in connection with moisture.”

In the mid-2000s, Dow made the same inaccurate marketing claims, eventually forcing the National Advertising Directive (NAD) to step in and arbitrate.

Betsy Steiner, currently the executive director of the EPS-IA characterizes the recent effort as “outlandish.” In May 2012, EPS-IA contacted Dow’s legal department with a formal request to cease publication and NAD attorneys have also contacted Dow.

The science behind EPS foam’s moisture resistance really isn’t in question. EPS’ closed-cell structure makes absorption and/or migration of moisture virtually impossible.

A study by the Energy Materials Testing Laboratories (EMTL) nearly 30 years ago proved that EPS insulation does not absorb appreciable moisture even in prolonged, cold, damp winters. The small amount it did absorb (an average of 0.2% by weight) has little or no effect on its insulative properties. The Minnesota Department of Public Service sampled seven-year-old EPS foundation insulation and found moisture levels of only 0.13%. This real-world example concluded that the EPS insulation retained between 95% and 97% of its thermal efficiency.

The biggest issue with using EPS below grade, such as ICF basement foundations, is the possibility of water finding its way into the structure. Because the concrete core is sheathed in foam, otherwise minor defects—like small voids (honeycombing) and hairline cracks—go unnoticed and under hydrostatic pressure, water can penetrate these areas of the wall. Finding these defects is costly, as the water can emerge on the interior face some distance from where the leak actually originates.

The recommended design for ICF foundations includes a waterproofing membrane (spray-applied or self-adhered), on the exterior face of the ICF, coupled with a reliable drainage system to eliminate the possibility of water infiltration.

Moisture from the Concrete
A second potential source of moisture originates in the construction materials themselves.

Wet concrete contains a tremendous amount of moisture: 35 gallons per cubic yard in a standard mix. Multiply that by the number of cubic yards placed in a footing, foundation, slab, and above-grade ICF walls, and it quickly becomes hundreds of gallons.

Only a percentage of that water added to concrete is used in hydration; the vast majority of it must evaporate off. This is easily accomplished when the concrete is placed as slabs or with removable forms. With ICFs, however, the concrete cures more slowly. Some have claimed that the foam sidewalls retard evaporation, creating the opportunity for mold growth on the inside face of the drywall.

Jake Vierzen, a Michigan-based ICF builder, has heard of that claim, and shuts it down quickly and effectively. “The short answer is that the perm rating of 2.5” of EPS is lower than that of 1/2” drywall,” he says, “so any vapor moving through the foam should easily dissipate through
the drywall.”

He continues, “This assumes that the area is properly vented and conditioned. Excess humidity has to be removed from the air, or it will condense somewhere.”

Back in 2002, the Portland Cement Association (PCA) funded a study to determine if ICF walls have any inherent properties that make them susceptible to moisture problems. The investigation was conducted in several phases. In the first phase, wall sections were constructed and instrumented to determine rates of drying with various combinations of exterior and interior finishes and vapor retarders. After one year of monitoring in a controlled atmosphere, the walls were carefully disassembled and examined for signs of moisture-related distress. (The second and third phases involved investigating the possibility of condensation and water ingress through improper detailing, and will be discussed later in this article. The complete report, entitled Investigation of Moisture in Insulating Concrete Form Walls, is available through the Portland Cement Association.)

“Questions have arisen as to whether the concrete contributes to moisture problems common in some climates,” write report authors John Gajda and Martha VanGeem. “Polystyrene insulation [is] relatively impermeable to water vapor transmission… and may slow the water vapor transmission.

To test this hypotheses, they constructed six sections of ICF wall, each measuring four feet square with a nominal 8-inch core. All were surfaced with painted drywall on one face. The other face was finished with one of three exterior finishes: acrylic stucco, cement stucco, or wood siding. Two samples were prepared for each finish, one directly attached or adhered to the foam, and the other with a vapor retarder/barrier (a clear 6-mil (0.15-mm) polyethylene). The sides of the wall sections were sealed to prevent moisture from escaping and to force all moisture migration through the interior and exterior finishes of the walls.

Wet footings can cause moisture to wick upwards through the concrete and release that moisture into the living space, as this concrete sample shows. A time-lapse video of the test is available at www.fab-form.com.

The concrete was a standard 3,000 psi mix with a 6½ in. slump, and the finishes were applied after 7 days. Then, the wall samples were stored and continuously monitored in a temperature and humidity controlled room for a period of one year. The nominal ambient conditions were 73ºF and 50% relative humidity.

When the year was complete, the walls were “disassembled and materials from the walls were visually examined for moisture-related damage such as mold, mildew, corrosion, rot, and fungi attack. The report concludes, “Visual inspection revealed that none of the building materials from any of the walls suffered from moisture damage.”

Douglas Bennion, technical director for Quad-Lock Building Systems, states, “The role that ICFs may play in the slower dissipation of mix water from concrete cannot automatically be linked to mold issues. Blaming the ICF is a lazy [and incorrect] answer.”

Other Construction Materials
Of course, concrete isn’t the only source of moisture in new construction. Wet framing materials, drywall mud, and paint also contribute to moisture.

If the building was built in a wet time of year, rain and snow can compound this moisture problem. ICF construction is tight enough that moisture that would typically dissipate naturally will need to be vented mechanically.

Mike Garrett, owner of BuildBlock Building Systems, says “I moved into my new ICF house early last year and as in the past with new homes, I had to address the moisture that is initially contained in all the building materials of the home. It makes no difference if the home is ICF or another form of construction, because the slab, crawl space, wood framing, ICF walls, cabinetry and carpet etc. all carry moisture.”

“The solution is to design the home properly with the right sized heat and air system,” he says. “Proper venting and mechanical equipment will keep humidity below 50%.”

A third potential source of moisture is condensation. For the PCA condensation study, twelve climates throughout North America were selected, representing a wide range of climates, but with a bias towards those with known moisture problems. The study modeled all of the exterior and interior finishes described earlier, as well as the role of exterior vapor retarders and interior vapor-retarding paint.

Gajda and VanGeem, the report authors, analyzed both winter and summer seasons for locations throughout North America and concluded that “to prevent condensation, a vapor retarder with maximum permeance of 0.1 perms is recommended between the insulation and interior finish(drywall) for Madison, Wisc. and colder climates.”

They note, however that the outdoor temperature conditions consisted of the ASHRAE winter and summer design conditions, which are more extreme than the real world. The report notes, “We… accept that the walls that exhibit potential condensation in the winter design condition do not during the average [real-world] January conditions… Recommendations regarding the use of vapor retarders in this report are conservative.”

Also, the analyses indicated that an exterior vapor retarder is not recommended in hot and humid climates because it can potentially cause condensation within ICF walls.

Technical experts with decades of ICF experience report that condensation is rarely a source of concern in the real-world. Kevin Rector, technical director at NUDURA, says that in his 15 years of providing ICF technical support across all the climate zones in North America, condensation has been an issue only once. The solution, again, was properly sizing the HVAC system.

“It was the result of an oversized A/C system delivering large volumes of cold air to a basement space in a very humid climate. As the cycle time for the A/C was so short, the moist air did not have a chance to flow past the A/C condensers and as a result, the moisture developed on the drywall surfaces, and over time this led to the mold condition,” he says. “Once a mechanical specialist was called in and the A/C unit was either downsized or adjusted to provide a longer cycle time, it fixed the problem.”

Garrett, at BuildBlock, adds, “As a manufacturer of ICF’s going on nine years we have had zero issues with mold in correctly vented or conditioned buildings. Only when improperly designed heating and cooling systems are installed have we ever had to address a concern. And even those are rare and usually easy to resolve.”

The Gypsum Association, a trade association for the drywall industry, has investigated this issue extensively, and their official publications report no problems with installing drywall directly over ICF. Their publication, Using Gypsum Board for Walls and Ceilings has an entire section dedicated to applying drywall over EPS foam (Section VII), and nowhere is application over ICF forbidden or even discouraged. The relevant section of Publication GA-238-03, Guidelines For Prevention Of Mold Growth On Gypsum Board simply reads, “Gypsum board must not be applied over other building materials where conditions exist that are favorable to mold growth.”

The EPS trade association is planning to collaborate with the Gypsum Association at some point to work up formal construction details for attachment of gypsum board to ICF.

Steiner says, “It is expected that securing these references to ICF construction in the Gypsum Association design manuals will be one of the first tasks to be delivered by EPS-IA’s ICF Work Group.” (This work group is the last vestige of the former ICFA.)

The fourth and final potential source of moisture is through improper detailing of wall penetrations, such as windows and doors. All reputable ICF manufacturers have developed details for roof/wall connections, window and door penetrations, exterior and interior finish attachment, and virtually every other conceivable application. These details have been around for more than a decade, and are designed to be” robust yet practical, with multiple layers of protection against infiltration of water.”

As long as the installer follows manufacturer-recommended detailing, the possibility of water infiltration is virtually zero.

They’re constantly updating these details based on the latest science. The nine leading ICF manufacturers are currently working with the Canadian Ready Mixed Concrete Association to test which window buck systems best prevent water ingress. First round testing was completed in the fall of 2011, with further tests last summer. Final results are expected in the coming months.

EPS Not a Food Source
For mold or mildew to be able to grow, three conditions must be met. The first—that their spores must be present—is guaranteed, as it’s impossible to prevent them from traveling. The second item—humidity above 50%–has already been addressed. The third factor is the presence of a food source.

ASTM C1338 (Standard Test Method for Determining Fungi Resistance of Insulation Materials and Facings) is the test criteria for mold growth. In 2004, generic ICF foam (regular 1.5 lb. rigid EPS) was tested by SGS US Testing Company, Inc., a trusted third-party laboratory.

The results demonstrate that EPS will not support mold growth. In fact, of the five common indoor mold types tested (Aspergillus Niger, A. Versicolor, A. Flavus, Penicillium Funiculosum, and Chaetomium Globosum), the lab reported that there was zero traces of growth over the 28-day incubation period.

Additionally, EPS foam’s resistance to mold or fungal growth is not due to any special additive. Unlike wood or drywall which is treated with pesticides and chemicals to make it rot resistant, ICFs are naturally mold-proof.

To prevent moisture problems with ICF construction,
the key likely lies with your HVAC designer. (For more information on how to properly vent an ICF home, see Air Exchangers and Energy Efficiency in the May/June 2012 issue of this magazine.)

Bennion, the technical expert at Quad-Lock, says, “The problem stems from inadequate ventilation, not ICFs. Mold cannot survive below about a 50% relative humidity condition. Listen to Joe Lstiburek: ‘Build tight and ventilate right.’ ”