--- title: Why Not To Install Fiberglass Insulation In Your Crawl Space description: Your crawl space needs insulation, but fiberglass is not the solution. Discover why fiberglass insulation should never be installed in a crawl space. image: https://scsfoam.com/hubfs/Article%20Title%20Images/Why%20Not%20To%20Install%20Fiberglass%20In%20A%20Crawl%20Space.jpg --- [Skip to main content](https://scsfoam.com/blog/fiberglass-insulation-crawl-space-problems#maincontent) [(717) 895-3498](tel:7178953498) [![South Central Services Insulation](https://scsfoam.com/hs-fs/hubfs/branding/Website%20Logo%20Classic.png?width=900&height=300&name=Website%20Logo%20Classic.png) ![South Central Services Insulation](https://scsfoam.com/hs-fs/hubfs/branding/Website%20Logo%20White.png?width=900&height=300&name=Website%20Logo%20White.png)](https://scsfoam.com/) [Our Service Areas](https://scsfoam.com/our-services-areas) Pricing - [Our Rates](https://scsfoam.com/our-rates) - [Calculators](https://scsfoam.com/pricing-calculators) - [Financing](https://scsfoam.com/financing-options/) - [Rebates](https://scsfoam.com/rebates) [Our Team](https://scsfoam.com/our-team) Services - Residential Insulation - [Attic Insulation](https://scsfoam.com/attic-insulation) - [Basement Insulation](https://scsfoam.com/basement-insulation) - [Crawl Space Repair](https://scsfoam.com/crawl-space-encapsulation) - [Commercial Spray Foam](https://scsfoam.com/commercial-spray-foam/) - [New Construction Insulation](https://scsfoam.com/new-home-construction-insulation/) - [Pole Building Insulation](https://scsfoam.com/pole-building-insulation) - [Air-Sealing](https://scsfoam.com/air-sealing) - [Blower Door Tests](https://scsfoam.com/blower-door-tests) [Our Products](https://scsfoam.com/our-products) Learning Center - [Learning Center](https://scsfoam.com/learning-center) - [Downloadable Resources](https://scsfoam.com/downloadable-resources) - [FAQ](https://scsfoam.com/faq/) Open Search [Get A Quote](https://scsfoam.com/contact/) Search for topics or resources Enter your search below and hit enter or click the search icon. 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Your energy bills are high, your floors are cold, and your house might even smell musty. While fiberglass is a popular insulation and is often installed in crawl spaces, the reality is that fiberglass should not be installed in crawl spaces. South Central Services has insulated hundreds of new and existing homes with spray foam. We have become well-versed in crawl spaces since southern Pennsylvania has many problematic crawl spaces. Many historic homes in Gettysburg, Fairfield, and Biglerville have crawl spaces with stone walls. We do not install fiberglass insulation in crawl spaces, and this article will explain why you shouldn’t either. By the time you finish reading, you will understand: - Why fiberglass insulation is not suitable for crawl spaces - Why there is no best fiberglass insulation for crawl spaces - What options you have to actually fix your problematic crawl space > Don't have time to read right now? Check out [everything you need to know at a glance](https://scsfoam.com/hubfs/At%20A%20Glance/Why%20Not%20To%20Install%20Fiberglass%20In%20A%20Crawl%20Space.pdf). ## Fiberglass Insulation Performs Poorly In Crawl Spaces. The number one reason you shouldn’t install fiberglass in your crawl space is because it will not perform. There are many reasons why fiberglass insulation does not work in a crawl space. These things cannot be fixed because they are the properties of fiberglass. Here’s a preview of why fiberglass doesn’t belong in a crawl space. 1. Fiberglass can’t handle moisture content 2. Fiberglass actually absorbs moisture 3. Fiberglass falls out of the ceiling 4. Fiberglass can’t create an effective barrier 5. Fiberglass is ideal for rodents to nest in Let’s examine all of these problems in greater detail. ### 1. Fiberglass Cannot Handle Moisture Content. Crawl spaces are below-grade spaces. The ground is dirt, and the walls are porous. Moisture from the ground surrounding your crawl space leaks inside. There is no sunlight to dry out the crawl space, so it faces excessive moisture compared to areas of the home aboveground. The excess moisture in your crawl space creates an ideal environment for mold and mildew to grow. Above the dirt floors and porous walls are wood flooring beams supporting some part of your house. In the worst cases, the excessive moisture in the crawl space contributes to mold and wood rot on these beams. What does fiberglass do about excess moisture? Fiberglass cannot do anything to stop it. On paper, fiberglass is a mold-resistant material. In real-life applications, fiberglass can contribute to mold growth in these conditions. ### 2. Fiberglass Absorbs Moisture. Not only does fiberglass not stop excessive moisture, but it also absorbs moisture. Moisture travels through the air in the form of vapor. When fiberglass is stuffed into the crawl space ceiling cavities, vapor can pass through cracks, crevices, and gaps. The fiberglass absorbs this vapor over time. Even if a fiberglass batt has a vapor barrier facing, any gap or cracks can allow vapor through to the interior of the fiberglass. ### 3. Wet Fiberglass Is Too Heavy For The Ceiling. What happens when fiberglass absorbs moisture? It becomes too heavy to stay in the crawl space ceiling. ![Batt insulation falling out of the ceiling of a crawl space in Franklin County, PA.](https://scsfoam.com/hs-fs/hubfs/Article%20Graphics/crawl%20space%20batt%20insulation.jpg?width=533&height=400&name=crawl%20space%20batt%20insulation.jpg) Fiberglass will fall to pieces and end up on the crawl space floor. The moisture content it absorbs tears it to shreds. > An insulation product can only be effective if it stays in place. Fiberglass is not appropriate for a crawl space, where exposure to vapor destroys the insulation. ### 4. Fiberglass Batts Form An Ineffective Barrier. Even if fiberglass insulation would stay snugly stuffed into the ceiling of your crawl space, it still would offer lackluster performance. Ignoring the issue of moisture, fiberglass is still ineffective in a crawl space. Batt insulation is prone to gaps. These small holes and cracks in the insulation barrier may not seem like a big deal. However, these gaps allow for air and vapor to pass through. Any gap in your fiberglass allows air to exchange between your crawl space and your living space. If we revisit the issue of excessive moisture, the air exchange between these two areas is unbalanced. You circulate clean and conditioned air in your living space to keep your family comfortable. In your crawl space, the air is dirty, damp, and musty. > Fiberglass and its gaps make it easy for these two types of air to exchange. Not only is this a consideration for your air quality, but it also impacts your energy bills. If you pay to keep the air in your living space at a particular temperature, the air from your crawl space will disrupt that temperature. This ineffective barrier leads to more cranking of the thermostat and more strain on your HVAC equipment. ### 5. Fiberglass Is A Tempting Home For Rodents And Pests. [No insulation is pest-proof.](https://scsfoam.com/blog/is-spray-foam-insulation-pest-proof) However, the nature of fiberglass is optimal for rodents to nest inside. If the insulation was not accessible to pests, this would not be a concern. But crawl spaces are below the ground. Rodents and other pests find their way inside of crawl spaces. The fiberglass that drips from the ceiling and lays on the floor frequently becomes home for rodents. There is nothing about the properties of fiberglass that can hinder these pest infestations. ## There Is No “Best” Fiberglass For Your Crawl Space. No matter what type of fiberglass batt you install, it will not offer the performance you need. Fiberglass was not built for below-grade applications like crawl spaces. Even the best fiberglass application, with no gaps and a vapor barrier facing, will experience all the downfalls we’ve already covered. The best installation of fiberglass is also still an impermanent solution. You cannot avoid the cycle of fiberglass becoming weighed down by moisture. > At some point, fiberglass in the crawl space will fail. In most applications, it doesn’t succeed even at the start. ## What Insulation Is Best For Crawl Spaces? At South Central Services, we recommend [encapsulation](https://scsfoam.com/blog/what-is-crawl-space-encapsulation). Encapsulation is a permanent solution for your crawl space. This method can [seal off entry points for pests](https://scsfoam.com/blog/how-to-keep-rodents-out-of-crawl-spaces). Most importantly, encapsulating will deal with the root moisture issues in crawl spaces. ![An encapsulated crawl space in Waynesboro, Pennsylvania with wrapped pillars, a vapor barrier floor, and closed cell spray foam on the walls.](https://scsfoam.com/hs-fs/hubfs/Article%20Graphics/encapsulated%20crawl%20space%20with%20pillars.jpg?width=533&height=400&name=encapsulated%20crawl%20space%20with%20pillars.jpg) An encapsulated crawl space is clean, dry, and accessible. Encapsulation invites air exchange between the living space and the crawl space because the crawl space no longer has dirty, unconditioned air. ## The Bottom Line About Why Fiberglass Doesn't Belong In Crawl Spaces Installing fiberglass insulation in your crawl space is a waste of your money. It may be tempting because fiberglass is inexpensive and often installed in crawl spaces. However, the properties of fiberglass insulation do not allow for success in a crawl space. Fiberglass cannot handle the excessive moisture in a crawl space and cannot solve the root problems causing high energy bills and musty smells. If you want to fix your crawl space, the solution you need is encapsulation. Encapsulation will be more expensive, but it is the only functional insulation option for crawl spaces in southern Pennsylvania. The unique problems that crawl spaces present require a solution that deals with moisture. Now that you understand why you shouldn’t install fiberglass in your crawl space, your next step is to: - [Discover more details about the encapsulation method](https://scsfoam.com/blog/what-is-crawl-space-encapsulation) - [Estimate how much encapsulating your crawl space will cost you](https://scsfoam.com/blog/encapsulation-cost-crawl-space-pa) - [Compare the types of insulations that can be installed in a crawl space](https://scsfoam.com/blog/types-of-insulation-for-crawl-spaces) [![SCHEDULE MY FREE SITE VISIT](https://no-cache.hubspot.com/cta/default/39735758/interactive-183818988836.png)](https://scsfoam.com/hs/cta/wi/redirect?encryptedPayload=AVxigLJiv1EbS0mPjQzfv8ZyyVU3g%2FsFUWcLma0zVIw1ne37FPwViLw7P8UQiEIQWhbTvrVnGmJxoMnUqXQmD25gBL1MiC%2FpOLtlZAbxkJhlRSH8zpqZc7%2B8PIYhb%2FLdiFDO4y1LF4EtVOo5b0elUxmfiwwt5O3enmJu2CdAy%2FgEJ1z4T5DPZCCOYwizfj%2BTwK7u2wKYRbjzkw%3D%3D&webInteractiveContentId=183818988836&portalId=39735758) *Disclaimer: While we strive to publish information accurate to building science, local building codes and standards supersede our recommendations.* [Alexis Dingeldein](https://scsfoam.com/blog/author/alexis-dingeldein) Alexis has been fascinated by spray foam insulation since 2018. When she isn’t thinking about insulation, Alexis is geeking out over storytelling and spreadsheets. Topics: [Building Science](https://scsfoam.com/blog/topic/building-science) [Crawl Space](https://scsfoam.com/blog/topic/crawl-space) Don't forget to share this post: ## Related Articles ### [Top 3 Places To Insulate In An Existing Home June 9th, 2025|5 min read](https://scsfoam.com/blog/top-places-to-insulate-in-an-existing-home) ### [What Is A Blower Door Test Used For? May 16th, 2025|2 min read](https://scsfoam.com/blog/what-are-blower-door-tests-used-for) ### [How Does Insulation Keep A House Cool? April 23rd, 2025|3 min read](https://scsfoam.com/blog/how-does-insulation-keep-a-house-cool) ### [What Is The R-Value Of Blown-In Insulation? April 4th, 2025|3 min read](https://scsfoam.com/blog/what-is-blown-in-insulation-r-value) ### [Can Insulation Be Reused? 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