When it comes to home insulation, the term “waterproof” is often thrown around, but does spray foam insulation truly live up to this claim? In this article, we will delve into the world of spray foam insulation to understand its waterproofing capabilities, benefits, limitations, and its role in protecting your home from moisture-related issues.

Understanding Spray Foam Insulation

Spray foam insulation is a popular choice among homeowners and builders due to its exceptional insulating properties. It is made from two components – polyurethane foam and a catalyst – which are mixed on-site and sprayed onto surfaces. As it expands and hardens, it creates an airtight seal that effectively prevents heat transfer, making it an excellent choice for energy efficiency. But what about its ability to repel water?

Water Resistance of Closed-Cell Spray Foam

There are two main types of spray foam insulation: closed-cell and open-cell. Closed-cell spray foam is renowned for its water resistance. Its dense, closed-cell structure makes it impermeable to water. When properly installed, closed-cell spray foam forms a continuous and seamless barrier that prevents moisture from infiltrating your walls, roof, or crawl spaces. This makes it an ideal choice for areas prone to heavy rains, flooding, or high humidity levels.

Open-Cell Spray Foam and Water Resistance

On the other hand, open-cell spray foam has a less dense structure and is not as effective at repelling water. While it can slow down the passage of moisture to some extent, it is not a waterproofing solution in itself. Open-cell spray foam is better suited for interior applications where moisture control measures are already in place, such as vapor barriers or dehumidifiers.

Benefits of Waterproofing with Closed-Cell Spray Foam

Protection Against Water Intrusion: Closed-cell spray foam creates a waterproof barrier that shields your home from rain, leaks, and groundwater. This is especially crucial in areas prone to flooding or heavy storms.

Reduced Risk of Mold and Mildew: By preventing moisture from entering your home’s structure, closed-cell spray foam reduces the risk of mold and mildew growth. Mold and mildew thrive in damp environments, and by keeping your home dry, you create a less hospitable environment for these harmful microorganisms.

Enhanced Structural Integrity: Water can weaken the structural integrity of your home over time. Closed-cell spray foam helps maintain the strength and durability of your walls and roof by keeping them dry and free from water-related damage.

Improved Energy Efficiency: In addition to its waterproofing benefits, closed-cell spray foam also provides excellent insulation, which can contribute to significant energy savings. By sealing gaps and preventing heat transfer, it reduces the need for constant heating or cooling, leading to lower utility bills.

Limitations of Spray Foam Insulation

While closed-cell spray foam offers exceptional waterproofing properties, it’s essential to acknowledge some of its limitations:

Cost: Closed-cell spray foam is relatively expensive compared to other insulation materials. However, many homeowners find that the long-term benefits outweigh the initial investment.

Installation Complexity: Proper installation is crucial for achieving the desired waterproofing and insulating effects. It requires skilled professionals who understand the nuances of spray foam application.

Vapor Barrier Required: In some cases, especially in colder climates, a separate vapor barrier may still be necessary in addition to closed-cell spray foam to prevent condensation issues.

Combining Waterproofing Strategies

While closed-cell spray foam can provide excellent waterproofing, it is often more effective when used in conjunction with other waterproofing strategies. These strategies can include:

Proper Drainage: Ensuring that water is directed away from your home’s foundation through grading, gutters, and downspouts.

Vapor Barriers: Installing vapor barriers in areas where condensation may occur, such as basements and crawl spaces.

Regular Maintenance: Conducting routine inspections and maintenance to identify and address any potential water-related issues promptly.

Quality Roofing: Ensuring your roof is in good condition with no leaks or damage.

Caulking and Sealing: Regularly inspecting and resealing areas around windows, doors, and other potential points of water entry.


In the world of home insulation, closed-cell spray foam stands out as an effective waterproofing solution. It creates an impermeable barrier that protects your home from moisture-related problems such as mold, mildew, and structural damage. However, it’s essential to consider the specific needs and challenges of your home when selecting an insulation and waterproofing strategy.

Ultimately, the decision to use spray foam insulation should be based on your climate, budget, and the expertise of your chosen contractors. When installed correctly and used in combination with other waterproofing techniques, closed-cell spray foam can help keep your home dry, comfortable, and energy-efficient for years to come.