Leveling a subfloor is a crucial step for ensuring a stable, long-lasting floor finish. This article examines the practice of using roofing felt to achieve a smoother, flatter surface, including when it might be appropriate, how to install it, and safer, more effective alternatives. It covers materials, preparation, step-by-step methods, potential drawbacks, and maintenance considerations to help homeowners and contractors make informed decisions.
Understanding The Role Of Roofing Felt In Subfloor Preparation
Roofing felt, traditionally used as a moisture barrier in roofing projects, is sometimes repurposed in flooring as a slip sheet or temporary leveling aid. While it can provide a uniform thickness when combined with other materials, roofing felt alone does not create a true, structural level. It may compress under load and fail to address high spots or dips in the framing. For best results, its use should be limited to specific situations and combined with additional leveling methods or underlayment products. Contractors should verify that the subfloor, joists, and local building codes support any unconventional approach.
When Roofing Felt Might Be Considered
In older homes or retrofit scenarios, roofing felt may be used as a temporary underlayment to even out minor irregularities before installing a more permanent leveling layer. It is sometimes employed as a moisture barrier beneath certain types of underlayment or finish flooring, rather than as the sole leveling solution. However, relying on felt alone to achieve a perfectly level surface is not recommended for modern flooring systems, especially with floating floors, hardwood, or tile. Always consult manufacturer guidelines for the final floor covering and local building codes before proceeding.
Recommended Tools And Materials For Subfloor Leveling
- Measuring tools: tape measure, straightedge, level
- Shims or self-leveling compounds (for more precise leveling)
- Plywood or OSB subfloor panels (if structural adjustments are needed)
- Roofing felt (as a moisture barrier or slip sheet, not the primary leveling layer)
- Adhesives: subfloor adhesive suitable for chosen flooring
- Fasteners: screws or nails rated for subfloor use
- Moisture barrier or vapor barrier (as required by flooring type)
- Cutting tools: utility knife, circular saw
- Safety gear: eye protection, gloves, dust mask
Step-By-Step: Using Roofing Felt In Conjunction With Other Leveling Methods
Note: Roofing felt is not a stand-alone leveling method. The following approach pairs felt with more reliable leveling practices to improve surface uniformity and protect against moisture.
- Assess The Subfloor: Inspect for loose boards, squeaks, rot, and excessive deflection. Mark high spots and low areas with a straightedge and level.
- Prepare The Surface: Remove debris, vacuum thoroughly, and repair damaged joists or plywood. Ensure the area is clean and dry before any layer is installed.
- Lay A Moisture Barrier: If moisture migration is a concern, install a proper moisture or vapor barrier according to flooring manufacturer guidelines, placing roofing felt as a supplementary layer only if advised by the professional.
- Level High Spots: Use shims or a self-leveling compound to address imperfections. For large dips, apply a structural fix such as sistering joists or replacing damaged framing before any overlay.
- Place Roofing Felt (Optional): If roofing felt is used as a slip sheet or moisture shield, cut to fit and lay flat, overlapping seams as required. Avoid creating a bumpy surface that could transfer to the finish layer.
- Install A Primary Leveling Layer: Apply a self-leveling underlayment or a plywood/OSB overlay to achieve a uniform plane. Follow manufacturer temperature and mixing instructions precisely.
- Secure And Cure: Allow the leveling product to cure per the product’s guidelines. Ensure the surface remains clean and undisturbed during curing to prevent ridges or bubbles.
- Apply Finish Flooring: Install the chosen floor covering (hardwood, laminate, vinyl, or tile) following the manufacturer’s substrate and installation guidelines.
Pros And Cons Of Using Roofing Felt For Subfloor Leveling
- Pros: Can act as a moisture barrier in some configurations; provides a uniform sheet that can reduce friction between layers; inexpensive on a per-square-foot basis in certain cases.
- Cons: Not a reliable leveling solution on its own; prone to compression under load; can trap moisture if not used correctly; modern flooring systems prefer dedicated underlayment and leveling compounds for consistent results.
Safer Alternatives For Achieving A Truly Level Subfloor
To ensure a durable, flat foundation, consider these proven methods:
- Self-leveling underlayment: A cementitious compound that flows to fill low areas and create a uniform surface. Ideal for concrete or damaged subfloors.
- Plywood or OSB overlay: Adds rigidity and smoothness, often combined with a ring-shank or ringed nail system to minimize movement.
- Shimming and sistering: Addressing high and low spots through targeted structural adjustments before overlays or finishes.
- Engineered floor underlayment: Combines moisture control with sound dampening and a flatter base for floating floors.
Moisture Management And Climate Considerations
Moisture is a critical factor in flooring performance. Use a proper moisture barrier under the subfloor or finish layer, especially in basements or high-humidity areas. Roofing felt may contribute as a barrier in specific configurations, but it should never substitute a tested moisture barrier or leveling system. Seasonal changes can cause wood to expand or contract; choose materials with appropriate permeability and follow acclimation guidelines.
Quality Control And Best Practices
- Follow Manufacturer Instructions: Always adhere to the specific guidelines for self-levelers, underlayments, and the final flooring product.
- Test In Small Areas: Check for a consistent plane across multiple sections before proceeding to full installation.
- Maintain Cleanliness: Keep the subfloor free of dust and debris to ensure proper adhesion of leveling compounds and underlayment.
- Allow Proper Curing Time: Do not rush the installation; curing times vary by product and conditions.
Common Mistakes To Avoid
- Using roofing felt as the sole leveling layer, expecting it to replace a proper leveling compound.
- Overlooking moisture problems that can cause bonding failures or veneer movement.
- Skipping structural repairs when there are deflections or damaged joists.
- Failing to acclimate plywood or other overlays in the intended environment.
Conclusion
While roofing felt can play a supporting role as a moisture barrier or slip sheet in some subfloor configurations, it should not be relied upon as the primary leveling method. For dependable results, combine felt with proven leveling products such as self-leveling compounds, plywood overlays, or structural fixes as needed. Adhering to manufacturer guidelines and building codes ensures a durable, flat subfloor ready for the chosen finish flooring.