Should You Use Tar Paper Under Wood Flooring? A Complete Guide to Felt Paper Underlayment

Should You Use Tar Paper Under Wood Flooring? A Complete Guide to Felt Paper Underlayment

If you have ever pulled up an old wood floor during a renovation, you have likely found a layer of dark, fibrous paper sandwiched between the subfloor and the planks. That material is tar paper, also known as asphalt-saturated felt paper, and it has been a standard component of wood flooring installation for well over a century. Builders and floor layers have relied on this humble underlayment to solve two persistent problems: moisture migration from below and the annoying squeaks that develop when wood rubs against wood over time. But does this traditional method still make sense with modern materials and techniques? This guide examines the purpose, benefits, limitations, and proper installation of tar paper under wood flooring so you can make an informed decision for your next project.

Understanding the Purpose of Tar Paper Under Wood Floors

Tar paper under wood flooring is not a random old-house curiosity. It serves specific functions that address fundamental challenges in wood floor performance and longevity.

What Is Tar Paper Made Of?

Tar paper, more accurately called asphalt-saturated felt paper, is manufactured by saturating organic felt (typically cellulose fibers from recycled paper) with hot asphalt. The result is a flexible, water-resistant sheet material that comes in various weights, most commonly 15-pound and 30-pound grades. The weight refers to the approximate mass per 100 square feet, with 30-pound felt being thicker and more resistant to moisture and tearing than 15-pound felt.

Rosin paper, a lighter and less expensive alternative, is sometimes confused with tar paper. However, rosin paper is saturated with rosin (pine resin) rather than asphalt, making it less effective as a moisture barrier. It can reduce noise between floor layers but does little to block moisture vapor.

The Two Primary Functions

As outlined in classic construction references and confirmed by flooring professionals, asphalt-saturated felt paper serves two main purposes under wood strip flooring:

• Moisture retarder: It blocks moisture vapor rising from the subfloor or crawlspace below, protecting the wood flooring from absorbing excess moisture that could cause cupping, crowning, or gaps between boards.
• Noise dampener: It provides a slip layer that reduces friction and cushioning between the subfloor and the finished flooring, minimizing the squeaks caused by wood-to-wood contact as the floor expands and contracts with seasonal humidity changes.

How It Differs From Modern Vapor Barriers

It is important to understand that tar paper is a vapor retarder, not a vapor barrier. True vapor barriers, such as 6-mil polyethylene sheeting, have a perm rating below 0.1 and block virtually all moisture vapor. Asphalt-saturated felt paper typically has a perm rating between 1 and 5, meaning it slows moisture migration significantly but does not stop it completely. This partial permeability is often desirable under wood flooring because it allows the wood to equilibrate gradually with the environment rather than trapping moisture or creating a completely sealed sandwich that could promote mold growth.

Key Benefits of Installing Felt Paper Underlayment

The benefits of using tar paper under wood flooring extend beyond moisture control and noise reduction. Understanding these advantages helps explain why the practice has persisted for generations.

Moisture Protection Across Different Subfloor Types

The moisture protection function becomes especially important in specific installation scenarios. The table below summarizes how tar paper performs across common subfloor conditions:

Noise Reduction and Squeak Prevention

Wood flooring expands and contracts with changes in indoor humidity. Over time, even well-installed floors can develop squeaks as boards rub against nails, the subfloor, or each other. The felt paper layer acts as a buffer, reducing friction and absorbing minor movements that would otherwise translate into audible noise. For existing homes with squeaky floor repair needs, installing felt paper during a reflooring project can prevent future noise problems that would be difficult to address after the floor is finished.

Protection During Construction

In new construction, the wood flooring is often delivered and installed before the building is fully sealed and climate-controlled. Tar paper provides temporary protection against dust, debris, and incidental moisture from other trades working in the space. It also creates a thermal break that reduces heat loss through the floor assembly, improving energy efficiency in homes with unconditioned spaces below.

When to Use Tar Paper and When to Choose Alternatives

Despite its long history and proven benefits, tar paper is not the right choice for every wood flooring installation. Modern products and installation methods have introduced new variables that must be considered.

Manufacturer Recommendations Take Priority

Before installing any underlayment, check the flooring manufacturer’s written instructions. Many manufacturers of prefinished engineered and solid hardwood floors specify exactly what underlayment products are approved for warranty coverage. Installing an unapproved underlayment, even one with a proven track record like tar paper, can void the warranty.

Some manufacturers now recommend a bead of urethane glue applied every 10 to 12 inches along the tongue of each plank rather than a loose-laid felt paper. The glue method prevents squeaks effectively but makes it impossible to use a continuous felt paper layer. In these cases, the manufacturer may direct you to seal the backs of the planks individually if moisture protection is a concern.

Situations Where Tar Paper Falls Short

There are several scenarios where tar paper is not the best choice:

1. Direct glue-down over concrete: When hardwood is glued directly to a concrete slab, a continuous vapor barrier rated for below-grade use is required. Standard felt paper does not provide sufficient moisture protection for this application.
2. Below-grade installations: In basements and other spaces below grade, where moisture vapor pressure is highest, a dedicated vapor barrier system is necessary. Felt paper alone is inadequate.
3. Radiant heating systems: Some felt paper products can insulate the floor and reduce heat transfer efficiency. Check with both the flooring and radiant heat system manufacturers for compatible underlayment recommendations.
4. Manufactured or engineered floating floors: These systems typically require a specific foam underlayment designed for the locking mechanism. Tar paper is not suitable for floating installations.

Alternative Underlayment Options

For situations where tar paper is not appropriate, several alternatives are available:

• Rosin paper: A lighter-duty option that reduces noise but offers minimal moisture protection. Suitable for above-grade installations in dry climates.
• Polyethylene film (6 mil): A true vapor barrier for below-grade and concrete slab installations. Not recommended for all wood floors due to potential moisture trapping.
• Combination underlayments: Modern products combine a vapor barrier layer with foam padding or built-in moisture management for specific flooring types.
• Urethane adhesive method: Glue strips or beads applied at intervals eliminate the need for separate underlayment while preventing squeaks.

For a detailed comparison of product categories, see our guide on hardwood flooring options and their recommended underlayment systems.

Best Practices for Installing Tar Paper Under Wood Flooring

If you decide that tar paper is the right choice for your project, following proper installation procedures is essential for achieving the intended benefits.

Material Selection and Preparation

Choose 15-pound asphalt-saturated felt paper for most above-grade installations over plywood or OSB subfloors. Use 30-pound felt for installations over crawlspaces or in regions with higher humidity. Store the felt paper in the installation area for at least 48 hours to allow it to acclimate to the room temperature and humidity.

Before laying the felt paper, ensure the subfloor is clean, dry, and flat. Sweep or vacuum thoroughly to remove any debris that could telegraph through the finished floor. Any protruding nails or staples should be set below the subfloor surface.

Installation Steps

1. Roll out the felt paper parallel to the direction of the flooring planks, starting at the longest wall.
2. Overlap each successive course by at least 2 inches at the seams and 4 inches at the end joints to ensure continuous coverage.
3. Fasten the felt paper with staples or roofing cap nails every 12 to 16 inches along the edges and every 24 inches in the field. Avoid over-fastening, which can tear the paper.
4. At walls and obstructions, cut the felt paper to fit with a sharp utility knife. Leave a slight gap at walls to allow for expansion.
5. If installing over a crawlspace, consider combining the felt paper with a basement vapor barrier system below the subfloor for comprehensive moisture management.
6. Begin installing the wood flooring immediately after the felt paper is laid. Avoid walking excessively on the exposed felt paper, which can tear or shift.

Common Mistakes to Avoid

Even experienced installers can make errors with tar paper underlayment. Watch out for these pitfalls:

• Using too few fasteners: Loose felt paper can bunch up or shift during flooring installation, creating bumps under the finished floor.
• Overlapping incorrectly: Seams that do not overlap adequately allow moisture to bypass the paper. Follow the direction of water flow: upper courses should overlap lower courses like roof shingles.
• Installing over damp subfloors: Felt paper slows moisture migration but cannot dry out a wet subfloor. Always check moisture content with a meter before installation.
• Combining incompatible products: Using felt paper over a polyethylene vapor barrier can trap moisture between the two layers, creating conditions for mold growth.
• Skipping the manufacturer check: As noted earlier, some modern flooring systems specifically prohibit felt paper underlayment. Always confirm compatibility before proceeding.

Final Considerations for Long-Term Performance

Tar paper under wood flooring remains a time-tested technique that delivers reliable results when applied correctly. It addresses the two most common complaints about wood floors: moisture damage and noise. However, the construction industry has evolved significantly since tar paper first became a standard practice. Modern flooring materials, adhesive systems, and climate control technologies have changed the installation landscape.

For most traditional nail-down wood floor installations over wood subfloors in above-grade applications, asphalt-saturated felt paper is still an excellent choice. It is affordable, easy to work with, and proven effective over decades of use. For specialized applications involving concrete slabs, below-grade spaces, radiant heat, or floating floor systems, consult the manufacturer specifications and choose an underlayment engineered for that specific condition.

The key is to understand what tar paper does well and where its limitations lie. By matching the underlayment to the specific conditions of your project, you can install a wood floor that performs beautifully for generations.