Using Roofing Felt as Floor Underlayment

Roofing Felt For Floor Underlayment is a question many remodelers and DIYers ask when seeking a low-cost barrier between subfloor and finish floor. This article examines material properties, installation methods, pros and cons, building code considerations, and better alternatives so readers can make an informed choice. Key takeaway: roofing felt can work in limited scenarios but often underperforms compared with purpose-built underlayments.

Factor	Roofing Felt	Purpose-Built Underlayment
Moisture Control	Limited	Designed For Flooring
Durability	Moderate	Higher
Cost	Low	Varies
Vapor Management	Poor	Engineered

Materials Overview: What Is Roofing Felt?

Roofing felt is a saturated or coated sheet product traditionally made from cellulose or fiberglass mat saturated with asphalt or bitumen. It is sold in rolls and commonly used as a weather barrier on roofs. It Is Not Engineered For The Traffic, Compression, Or Vapor Control Required For Flooring Systems.

How Roofing Felt Compares To Flooring Underlayment

Floor underlayment options include kraft paper, foam, cork, rubber, cement board, and specialized synthetic felts. These are engineered for load distribution, moisture control, sound attenuation, and sometimes thermal insulation. Roofing felt lacks many of these tailored properties, especially in moisture and vapor management.

Thermal And Acoustic Performance

Roofing felt provides minimal sound deadening and little thermal benefit compared with foam or cork underlayments. For floating floors where sound and comfort are important, purpose-designed underlayments perform significantly better. Roofing Felt Offers Lower R-Value And Acoustic Attenuation.

Compression And Load-Bearing

Flooring systems face concentrated loads from furniture and foot traffic. Roofing felt can compress and wrinkle, causing movement in thin finishes such as vinyl or laminate. Specialized Underlayments Maintain Stable Thickness Under Load.

When Roofing Felt Might Be Acceptable

In dry, low-traffic secondary spaces—like attics converted to storage or temporary subfloors—roofing felt may serve as a short-term slip or dust barrier. It can also be used under rough-in layers where long-term performance is not expected. Use Roofing Felt Only For Short-Term, Low-Risk Applications.

Moisture And Vapor Considerations

Roofing felt is not a vapor barrier; it can absorb moisture and transfer it between wood layers. This may promote cupping, mold, or adhesive failure in flooring finishes. For installations over concrete slabs or in basements, a proper vapor retarder or vapor-permeable underlayment is essential. Incorrect Moisture Management Is The Leading Cause Of Flooring Failures.

Concrete Slabs And Basements

When installing over concrete, a vapor barrier meeting ASTM standards is recommended. Roofing felt does not meet these requirements and can trap moisture against wood subfloors, causing long-term issues. Do Not Substitute Roofing Felt For A Qualified Vapor Retarder Over Slab.

Installation Guidelines If Roofing Felt Is Used

If a project requires roofing felt as an interim underlayment, follow specific steps: ensure subfloor is clean, flat, and dry; lay felt flat with staggered seams; fasten per manufacturer guidance and overlap edges; avoid adhesive-dependent finishes directly over felt. Proper Installation Reduces But Does Not Eliminate Risk.

1. Acclimate materials and verify subfloor moisture.
2. Lay felt with 2–4 inch overlaps and seal seams with compatible tape.
3. Use mechanical fasteners to avoid movement; avoid troweled adhesives on felt.
4. Test a small area with the planned finish to confirm adhesion and flatness.

Compatibility With Common Flooring Types

Roofing felt can interact poorly with some finishes. Engineered hardwood, vinyl, and tile often require a stable, non-absorbent underlayment and, in some cases, adhesive bonding that roofing felt will inhibit. Ceramic Tile And Glue-Down Vinyl Typically Require Approved Underlayment Systems.

Floating Floors (Laminate, Click-Lock)

Floating floors often allow a broader range of underlayments; thin roofing felt may function as a slip layer but can compress, causing gaps and squeaks. Foam or combined foam-vapor barrier underlayments are preferable. Choose Underlayments That Maintain Thickness And Provide Vapor Protection.

Glue-Down Floors

Adhesive-based installations need clean, compatible substrates. Roofing felt can prevent adhesives from bonding and may degrade under solvent-based glues. Always Use Manufacturer-Approved Underlayments For Glue-Down Systems.

Durability, Lifespan, And Maintenance

Roofing felt has limited long-term durability when used under floors; it may degrade under foot traffic and moisture cycles. Over years, seams can open and the material can become crumbly. Routine inspections and prompt repairs are necessary if roofing felt is used. Expect Shorter Service Life Compared To Flooring Underlayments.

Cost, Availability, And Environmental Factors

Roofing felt is inexpensive and widely available at most building supply stores, making it tempting as a budget choice. However, potential repair costs and replacement of failed flooring often exceed initial savings. Consider recycled-content underlayments or cork for environmentally conscious projects. Low Initial Cost Can Translate To Higher Long-Term Expenses.

Building Codes, Warranties, And Insurance Implications

Many flooring manufacturers void warranties if unapproved underlayments are used. Local building codes or inspectors may also require specific materials or vapor control for conditioned spaces. Using roofing felt where codes require a vapor barrier can create compliance and insurance issues. Verify Manufacturer Requirements And Local Codes Before Using Roofing Felt.

Alternatives To Roofing Felt For Floor Underlayment

Consider these common alternatives: polyethylene vapor retarders, foam underlayment with integrated vapor barrier, cement backer board for tile, cork for natural insulation, and rubber or felt underlayment made for flooring. Each option addresses specific performance needs. Select Underlayment Based On Moisture Control, Load, And Acoustic Needs.

Floor Type	Recommended Underlayment
Floating Laminate/Vinyl	Foam Or Combined Foam/Vapor Barrier
Glue-Down Vinyl	Manufacturer-Approved Primers/Underlayments
Ceramic/Porcelain Tile	Cement Backer Board Or Uncoupling Membrane
Engineered Hardwood	Felt Or Cork Specifically Rated For Flooring

Best Practices And Practical Recommendations

When considering roofing felt for floor underlayment, prioritize long-term performance: check moisture with a reliable meter; follow manufacturer guidance for both flooring and underlayment; use a vapor barrier over concrete where required; and test compatibility with adhesives and finishes. When In Doubt, Choose A Product Designed For Flooring Applications.

Case Examples And Real-World Outcomes

Contractors report mixed outcomes: short-term success in dry closets or attic subfloors, and failures where roofing felt was used under glue-down vinyl or in high-moisture environments. These real-world examples emphasize matching material properties to application demands. Real-World Failures Often Stem From Moisture And Adhesion Issues.

Summary Checklist For Decision-Making

Before using roofing felt as floor underlayment, run through this checklist: Is the space dry and low-traffic? Does the flooring manufacturer allow nonstandard underlayments? Will moisture vapor be present? Can a purpose-built underlayment be used instead? Answering No To Any Question Should Prompt Choosing A Different Underlayment.

• Confirm Subfloor Flatness And Dryness
• Check Flooring Manufacturer Warranties
• Consider Long-Term Durability And Maintenance
• Verify Local Building Code Requirements

Where To Find Professional Guidance

Consult licensed contractors, local building inspectors, or flooring manufacturers for project-specific recommendations. Independent third-party labs publish standards (ASTM) for vapor retarders and underlayment performance, which can guide material selection. Professional Guidance Reduces Risk And Protects Warranties.

This article equips readers with detailed, practical information about Roofing Felt For Floor Underlayment, helping them weigh cost, performance, and code implications to choose the right underlayment for each flooring project.