Roofing Felt as Floor Underlayment: Pros, Cons, and Setup

Roofing felt, commonly used as an underlayment in roofing projects, is sometimes considered for floor applications. While not a mainstream choice for interior flooring, understanding its properties, installation methods, and limitations helps homeowners and contractors make informed decisions. This article explores when roofing felt can be used as a floor underlayment, how it compares to traditional underlayment materials, and practical steps for safe, effective installation in American homes.

Overview Of Roofing Felt For Underlayment

Roofing felt is a sheet material made from asphalt-impregnated paper or fiberglass, designed to provide a secondary barrier against moisture and minor surface irregularities. When used as a floor underlayment, its primary role is to create a smooth, moisture-resistant layer between the subfloor and the final floor finish. It is most often encountered in temporary or specialized installations rather than standard residential projects. The performance of roofing felt in a floor context depends on weight (measured in pounds per square), type (paper versus fiberglass), and the presence of self-adhering backing or moisture barriers.

Material Types And Properties

Understanding the main types helps determine suitability for floor use. Asphalt Saturated Paper Felt offers basic moisture resistance and can compress under load, potentially affecting floor flatness. Fiberglass-Backing Felt provides greater tear resistance and dimensional stability, though some products may be brittle with temperature changes. Self-Adhering Roofing Felt has a sticky backing for easier fastening and can seal joints, which can help when used as a vapor barrier in certain floor assemblies. In all cases, the underlayment should lie flat with no wrinkles, and overlaps should be sealed or taped to prevent gaps that telegraph through the finish.

When To Use Roofing Felt Underlayment On Floors

Roofing felt may be considered in specific scenarios. It can serve as a temporary moisture barrier during construction or in utility spaces where a lightweight, inexpensive layer is acceptable. Some older homes used asphalt-impregnated sheets as an inexpensive subflooring companion in certain climates. However, for typical living spaces with wood or concrete subfloors, dedicated floor underlayment materials—such as foam, cork, or cork-based blends, or cementitious underlayments—offer superior performance in moisture control, sound attenuation, and installation consistency. It is essential to check local building codes, manufacturer guidelines, and the specific floor finish requirements before selecting roofing felt for a floor underlayment.

Installation Considerations

Proper installation is critical to avoid failures. For any underlayment, ensure a clean, dry, flat subfloor. If used as a temporary moisture barrier, roofing felt should be placed with the smooth side up and seams overlapped in the direction of the anticipated load. For self-adhering variants, remove the release paper gradually to avoid air pockets, and press firmly to prevent wrinkles. When used beneath floor finishes that require consistent bonding, such as vinyl or tile, check compatibility with adhesives and thinset mortars. Pay attention to expansion gaps around edges and at seams, and avoid stacking felt layers, which can create height mismatches and telegraphing through the finished surface.

Compatibility With Subfloors And Adhesives

Subfloor compatibility is a core concern. On wood subfloors, roofing felt can mask minor imperfections but may compress under heavy traffic, creating squeaks or unevenness if the final floor is not properly bonded. On concrete slabs, moisture vapor transmissions must be managed through a purpose-built vapor barrier system; roofing felt alone is rarely sufficient. Adhesive compatibility varies by product and flooring type. Some adhesives may not bond well to asphalt-impregnated felt, leading to delamination or premature wear. Always test a small area and follow the manufacturer’s installation instructions for the final floor finish.

Pros And Cons

• Pros: Inexpensive, lightweight, readily available, easy to cut, offers a basic moisture barrier in some contexts, and can be used as a temporary underlayment during construction.
• Cons: Limited moisture protection compared to dedicated underlayments, potential for compression and telegraphing through finished floors, compatibility concerns with adhesives and finishes, reduced comfort and sound attenuation, and not typically approved by modern building codes for long-term floor use.

Alternatives To Roofing Felt For Floor Underlayment

Several alternatives provide better performance for most interior floors. Foam Underlayment (polyethylene or cross-linked polyethylene) offers excellent impact resistance and sound reduction. Cork Underlayment combines comfort and moisture resistance for certain applications. Particleboard Or Plywood Subfloors With A Mortar Bed is common under ceramic tile with a dedicated waterproof membrane. Cement-Based Underlayments provide a rigid, moisture-tolerant base for stone or tile. Lastly, vinyl or engineered wood underlayments are designed to work with specific flooring products, ensuring warranty compliance and consistent performance. Always match underlayment to the final floor finish and subfloor type, guided by manufacturer recommendations and local codes.

Maintenance And Longevity

When roofing felt is used as a floor underlayment, regular inspection is prudent. Look for signs of moisture intrusion, wrinkling, tearing, or adhesive failure. Address any moisture source promptly to prevent mold growth and structural damage. Replacement intervals for underlayment materials vary; most traditional underlayments are designed for single-use installations with the final floor. If roofing felt is retained, ensure there is no trapped moisture beneath it and that the final finish has appropriate vapor control. Routine cleaning and occasional checks after seasonal changes help maintain performance and prevent long-term issues.

In summary, roofing felt can function as a basic underlayment in select, non-critical applications, or as a temporary barrier during construction. For standard residential flooring, modern underlayment materials provide superior moisture control, sound attenuation, and compatibility with common finishes. When selecting materials, prioritize the final floor type, subfloor condition, and local building codes to ensure long-term durability and warranty compliance.