Roofing Felt Under Hardwood: A Comprehensive Guide for Homeowners
Roofing felt, traditionally used as underlayment for roofs, sometimes appears in discussions about hardwood flooring as a potential moisture barrier or temporary layer. This article explains when roofing felt might be used under hardwood, its benefits and drawbacks, installation considerations, and practical alternatives aligned with common U.S. building practices. Readers will learn how to evaluate moisture control, subfloor compatibility, and code requirements to make an informed decision.
What Roofing Felt Is And How It Works Under Hardwood
Roofing felt, also known as tar paper or mineral-saturated felt, is a fibrous sheet saturated with asphalt. In roofing, it serves as an additional moisture barrier and provides a stable surface for shingles. When used under hardwood flooring, felt can act as a temporary barrier or a simple spacer, but it is not designed as a long-term subfloor moisture control solution. Its performance depends on the type (15-lb, 30-lb, or heavier) and exposure to humidity, temperature changes, and foot traffic. Important distinctions include its permeability, durability, and tendency to compress over time, which can affect floor stability and acoustics.
Reasons Homeowners Consider Roofing Felt Under Hardwood
Several scenarios prompt consideration of roofing felt beneath hardwood:
- Temporary moisture barrier during construction or restoration.
- As a temporary spacer for leveling or accommodating seasonal shrinkage and expansion.
- To provide a uniform thickness when transitioning from one subfloor system to another.
- In retrofits where existing underlayment is damaged or unavailable.
Key consideration: roofing felt is not a substitute for proper underlayment designed for hardwood flooring or a dedicated vapor barrier, and it may not meet contemporary building codes or flooring manufacturer guidelines.
Moisture, Subfloor, and Code Considerations
Moisture management is critical for hardwood longevity. Modern underlayment for hardwood typically includes a breathable or moisture-vapor-retardant layer designed to work with a specific subfloor and finish system. Roofing felt alone can trap moisture or create a false sense of protection. Before using felt, evaluate:
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- Subfloor type (plywood, OSB, concrete slab) and its moisture content.
- Presence of a vapor barrier or radiant heat system beneath the subfloor.
- Manufacturer recommendations for the hardwood species, finish, and installation method (nailed, stapled, or floating).
- Local building codes and contractor guidelines, which may prohibit felt as a permanent underlayment.
In basements or crawl spaces with high humidity, relying on felt as a moisture barrier is generally discouraged. Persistent moisture can lead to mold, cupping, or gaps between boards. Always perform a moisture test and consult the flooring manufacturer’s installation instructions before proceeding.
Installation Considerations If Felt Is Used Temporarily
If felt is used temporarily during construction, follow these best practices to minimize risk:
- Choose a light to moderate weight felt (e.g., 15-lb) and avoid heavy, adhesive-backed varieties that can leave residue.
- Lay felt flat with minimal folds, ensuring seams do not overlap too aggressively, which can create high spots under the hardwood.
- Do not rely on felt as a long-term moisture barrier; plan to install the proper underlayment recommended by the hardwood manufacturer before finishing the floor.
- Control indoor humidity during and after installation to reduce movement and potential gaps.
Important: If the project transitions from temporary to permanent, remove the felt and replace it with the correct underlayment specified by the hardwood and subfloor system.
Alternatives to Roofing Felt for Hardwood Underlayment
Several modern options offer superior performance for hardwood compared to roofing felt:
- Polyethylene or Polypropylene Underlayment: Provides vapor control and moisture resistance while remaining lightweight and easy to install.
- Cork or Rubber Underlayment: Offers sound insulation, some moisture resistance, and comfort underfoot.
- Foam Underlayment: Economical choice with impact and sound-dampening properties; works well with floating floors.
- Breathable Plywood Underlayment: Combines structural support with a barrier that reduces moisture transfer when paired with a proper top vapor barrier.
When selecting an underlayment, consider:
- Moisture management aligned with the subfloor and climate zone.
- Acoustic performance, especially in multi-story homes.
- Compatibility with the hardwood finish and installation method.
- Warranty requirements from the flooring manufacturer.
Practical Steps for a Safe, Durable Hardwood Installation
To ensure a durable floor regardless of whether felt is involved, follow these steps:
- Assess the subfloor condition for flatness, dryness, and clean surfaces. Fix any protrusions or dips before installation.
- Follow the hardwood manufacturer’s substrate and underlayment requirements precisely. Use the recommended underlayment type and thickness.
- Test humidity levels in the installation space. For concrete slabs, ensure adequate moisture mitigation per the concrete slab’s moisture content and the flooring product’s guidelines.
- Acclimate hardwood boards to room conditions for the recommended duration.
- Install with proper fasteners, spacing, and alignment to prevent gaps and cupping.
- Seal or finish the wood as directed, maintaining climate control to minimize movement after installation.
Common Questions About Roofing Felt Under Hardwood
Below are frequent concerns homeowners raise about this topic:
- Is roofing felt allowed under hardwood? Some installations permit felt as a temporary measure, but it is not generally recommended as a permanent underlayment due to moisture and durability concerns. Always consult the flooring manufacturer and local codes.
- Will felt protect hardwood from moisture? Felt provides limited protection and should not replace a purpose-built moisture barrier or breathable underlayment specified by the manufacturer.
- What happens if I skip proper underlayment? Inadequate underlayment can lead to uneven floors, squeaks, and premature wear of the finish.
Conclusion: Make An Informed Choice For Longevity
Roofing felt is not a standard or recommended underlayment for most hardwood installations in the United States. While it may serve a temporary purpose during construction, reliable moisture management and compatibility with the flooring system require purpose-built underlayment and adherence to manufacturer guidelines. Homeowners should consult hardwood manufacturers, local building codes, and licensed flooring professionals to select the correct underlayment and ensure a durable, aesthetically pleasing floor.