Roofing felt, also known as tar paper, is a traditional moisture barrier used in roofing and some subfloor applications. When considering wood floor underlayment, homeowners and contractors weigh its cost, availability, and performance against purpose-made underlayments. This article examines whether roofing felt is suitable for wood floor underlayment, outlines installation steps if chosen, and compares it with modern alternatives to help readers make an informed decision in the American market.
Overview Of Roofing Felt As Underlayment
Roofing felt is an asphalt-saturated felt material available in 15-pound, 30-pound, or heavier grades. In wall and roofing assemblies, it acts as a moisture barrier and secondary weather protection. Some DIY projects and older homes show roofing felt used beneath wooden floors to provide a temperate surface and slight sound dampening. However, it is not specifically designed for acoustic performance, stability under foot traffic, or long-term flooring integrity for interior installations. When used as a floor underlayment, its thickness and dimensional stability are major considerations that influence floor flatness, fastener penetration, and seam behavior.
When Roofing Felt Might Be Considered
Roofing felt may be considered in the following scenarios, though it is generally a last-resort option rather than a standard solution:
- Emergency or temporary installations where no dedicated underlayment is available.
- Renovations in older homes where cost savings are prioritized and the subfloor is already solid and flat.
- Under certain types of vinyl or laminate flooring where a low-cost moisture barrier is desirable and local codes allow it.
Installation Steps If Roofing Felt Is Used
When opting to use roofing felt as subfloor underlayment, follow careful steps to maximize performance and minimize risks. Preparation and precise installation are critical to reducing squeaks and ensuring evenness.
- Inspect the subfloor for planks, cupping, or unevenness. Repair major defects before proceeding.
- Choose the correct felt weight. A lighter 15-lb or mid-range 30-lb felt is more common; avoid very heavy grades that can create excessive thickness and reduce floor height consistency.
- Clean the subfloor and ensure a dry, dust-free surface. Any debris can create ridges under the floor finish.
- Lay the felt with an overlap of 2 to 4 inches and stagger seams like a roof installation. Do not leave gaps that could trap moisture or create trip hazards once covered.
- Attach using staples or roofing nails specifically rated for interior use, following the product’s recommendations for fastener type and spacing. Keep fasteners flat to avoid protrusions that can damage the wood flooring.
- Check for levelness after installation. Use a straightedge to identify high or low spots, and address them before laying the wood flooring.
- Install the wood floor according to the manufacturer’s guidelines, paying attention to expansion gaps at walls and around any fixed features.
Pros And Cons Of Using Roofing Felt As Underlayment
Understanding the trade-offs helps determine if roofing felt is appropriate for a specific project. Below are the primary advantages and disadvantages.
- Pros
- Low cost relative to specialty underlayments
- Simple availability in most hardware stores
- Potential moisture barrier benefit under certain flooring types
- Cons
- Limited dimensional stability can result in ridges or dips under the finished floor
- Not designed for long-term performance as an interior underlayment for hardwood or engineered wood floors
- May compromise flush installation and impact floor finish durability if seams or staples loosen over time
- Can increase overall floor height, affecting transitions to adjacent rooms and doors
Better Alternatives For Wood Floor Underlayment
For most wood flooring projects, dedicated underlayments provide superior performance. These options improve acoustics, moisture control, and surface flatness while maintaining compatibility with wood floors.
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- Felt-lined underlayments (rosin paper, synthetic felt variants) designed for interior use
- Plywood or thin subfloor overlays to achieve a uniform, smooth base
- Foam or cork underlayments offering good sound dampening and moisture resistance
- Rubberized asphalt or polyethylene underlayments optimized for engineered hardwood and laminate
- Acoustic underlayments with specific STC/IIC ratings for improved room acoustics
When selecting an underlayment, consider moisture exposure, substrate condition, flooring type, and room use. Always follow the flooring manufacturer’s recommendations for underlayment and installation methods to maintain warranty coverage and performance.
Moisture Management And Subfloor Preparation
Regardless of underlayment choice, moisture management is critical in wood floor installations. Concrete slabs, wooden subfloors, and moisture-prone spaces require proper testing and control measures. Use a moisture barrier when moisture migration is a concern, especially in basements or ground floors. Thoroughly dry the subfloor and use a moisture meter to verify levels before installing wood flooring. Address any elevated humidity or condensation to prevent cupping, warping, or staining after installation.
Code And Warranty Considerations
Local building codes and flooring manufacturer warranties often specify acceptable underlayment types and installation methods. Using roofing felt as a primary underlayment may void warranties or fail to meet code requirements in some jurisdictions. Always consult local codes and review the wood floor manufacturer’s installation instructions before proceeding. When in doubt, choose a purpose-built underlayment designed for interior wood floors to ensure compliant performance and warranty protection.
Practical guidance For Homeowners
For a practical path to durable wood floors, consider the following guidelines. First, evaluate subfloor condition, moisture risk, and room environment. If the subfloor is flat and dry, a dedicated underlayment designed for wood floors generally provides the best results. If budget or availability constraints exist, roofing felt can be used temporarily with careful installation but plan for replacement with a proper underlayment as soon as feasible. Maintain cleanliness during installation and ensure consistent seam overlap and fastener placement to minimize future issues.