When purchasing a home in the Chicago metropolitan area, discovering visible issues such as condensation, moisture damage, mold, high humidity, HVAC performance issues, bubbling paint, or rotting roof decking is alarming, especially if the home was built or retrofitted with spray foam insulation. While spray foam is a premium insulation solution for cold climates like Chicago’s, it can contribute to severe indoor air quality and structural problems if improperly installed or not paired with adequate ventilation. This article examines the significance of these signs, how to evaluate the risks, and the necessary steps to restore the home to a safe, comfortable, and efficient state.

Red Flags: What to Watch For

1. Condensation on Windows or Walls:
   In spray foam homes, visible condensation is a significant warning sign. Because spray foam creates an airtight envelope, trapped humidity has no place to escape. In older homes retrofitted with foam, this issue is often exacerbated by inadequate HVAC systems, overuse of whole-house humidifiers, lack of appropriately installed bath fans, either vented into the attic or not existing at all, or the absence of mechanical ventilation (ERV/HRV or similar). In newer homes, it may indicate a design flaw or poor quality control.

2. Moisture Stains or Mold:
   Brown or black stains on drywall, ceilings, or attic decking—particularly in corners or near ceiling penetrations—often signal moisture intrusion. Mold requires moisture and organic material to grow, and in tightly sealed homes, even minor roof leaks or thermal bridging can create hotspots where mold thrives undetected.

3. Bubbling or Peeling Paint:
   This is often a sign of vapor being trapped behind painted surfaces. In Chicago, where exterior walls are subject to both freezing winters and humid summers, improper vapor barrier management (or lack of drying ability in wall assemblies) can lead to surface bubbling, cracking, or peeling of paint.

4. Roof Decking Issues:
   Spray foam applied directly to the underside of roof sheathing without a ventilation strategy can trap moisture. Especially during Chicago’s freeze-thaw cycles, this can lead to rot, mold, and delamination of plywood or OSB roof decks. If you see sagging, staining, or mold on the underside of the roof, this could be the issue.  At closing, removal of the drywall on the interior will be required to confirm the specifics of what is happening and how it needs to be addressed.

5. High Indoor Humidity or Musty Odors:
   Homes with 60 %+ relative humidity in summer or persistent musty smells often have poor air exchange rates. Without a whole-house dehumidifier or fresh air intake, the indoor environment may become increasingly unhealthy over time, despite appearing energy-efficient on paper.

6. If you have access to “seeing” the foam, is it of good quality, consistent in color? 
   Is it “Frankenstein” foam, where it is a mixture of foams of dramatically different depths, some hard and some soft, all sprayed in the same area? Is there a sticker on the electric panel identifying the installer, brand, and depths of foam installed?  Is there foam touching or sprayed over existing fiberglass or other types of insulation, a clear indication that something is “right” with the installer and their understanding of how to install foam insulation? Something we see far too often.

Causes of These Problems in Spray Foam Homes

In the Chicago region, a combination of climate, insulation type, and ventilation system affects how homes handle moisture. Spray foam homes that experience these problems often share these characteristics:

• Inadequate Ventilation:
  Chicago homes built with spray foam are often too airtight. Without mechanical ventilation systems, such as a Heat Recovery Ventilator (HRV) or an Energy Recovery Ventilator (ERV), stale, humid air is trapped inside.

• Oversized HVAC Systems:
  Many older homes retrofitted with foam insulation were not reengineered to accommodate new heating and cooling loads. An oversized AC cools too quickly without running long enough to dehumidify. That’s a huge issue during hot, humid Chicago summers.

• Incorrect Application of Foam:
  Poor application—such as spraying over wet surfaces, failing to achieve complete coverage, or applying an improper thickness—can trap moisture behind the foam, leading to hidden rot or mold. This is especially risky in roof assemblies, cathedral ceilings, or dormer walls.

• Lack of Vapor Control in Wall Assemblies:
  In cold climates like Chicago’s, improperly detailed wall assemblies can allow warm interior air to condense inside wall cavities. Closed-cell spray foam serves as a vapor retarder; however, without a strategic approach to wall drying (either inward or outward), moisture can become trapped.  Open-cell foam in walls and roofs is fine when supported by documentation and sprayed to the required depths in those areas.  Open-cell foam should be used rarely, if at all, for direct spraying against masonry surfaces; exceptions exist, but they are rare.

Real-World Examples and Case Studies

1. Suburban Chicago Retrofit Gone Wrong:
   A homeowner in Skokie retrofitted a 1970s split-level home with closed-cell foam in the attic and rim joists but failed to install mechanical ventilation. Within a year, paint began bubbling in the upstairs bedrooms, and black mold was discovered behind the drywall. Solution: They installed an ERV and a whole-house dehumidifier and replaced the drywall and sheathing in key areas, at a cost of nearly $20,000.

2. Lincoln Park New Construction Nightmare:
   A luxury builder sprayed closed-cell foam in a new row home in Lincoln Park. The HVAC system wasn’t downsized or rebalanced. During the first summer, the house felt clammy, and the ceiling paint in the top-floor bedrooms bubbled. The roof deck was found to have mold and required partial removal and replacement of the sheathing. The fix included adding mechanical ventilation in the form of an HRV, reducing AC tonnage, and adding a ducted dehumidifier.

3. Lake County Ranch House Misstep:
   In this case, an older ranch home was upgraded with spray foam in the crawl spaces and rooflines. Unfortunately, open-cell foam was used in the crawl space, and venting was sealed off. This created a humid pocket under the home. Floor joists began to rot, and occupants developed respiratory symptoms. A local contractor installed and removed the open-cell foam, then installed closed-cell foam over the vents and ground, sealing out both cold and moisture, allowing the home to remain comfortable while keeping the moisture and cold out of the crawlspace—total cost: $12,000.