Understanding the Purpose of Tar Paper Under Wood Flooring
When installing wood flooring, the materials you place beneath the planks matter just as much as the flooring itself. One traditional yet highly effective underlayment is tar paper, also known as asphalt-saturated felt paper. For decades, builders and flooring specialists have relied on this material to create a more durable wood floor assembly. Whether you are working with wide pine planks in a historic renovation or installing new hardwood in a modern home, understanding why tar paper is used can make a significant difference in the final result.
The primary role of tar paper as an underlayment is twofold. First, it acts as a moisture retarder, preventing ground moisture from migrating up through the subfloor and into the wood flooring above. Second, it helps to diminish noise caused by wood-to-wood contact between the flooring and the subfloor. These two benefits alone make tar paper an attractive option for many flooring projects. For a broader overview of wood flooring options and their requirements, see our guide on wood flooring types and selection.
Moisture Retardation: The First Line of Defense
Moisture is one of the greatest enemies of wood flooring. When moisture seeps into wood planks from below, it can cause cupping, buckling, warping, and eventually rot. Tar paper provides a reliable barrier that slows the movement of moisture vapor from the subfloor into the flooring material. This is especially important when installing wood flooring on the first floor over a basement, crawlspace, or concrete slab.
- Tar paper has a permeability rating that allows it to block liquid moisture while permitting some vapor transmission, avoiding trapped moisture that could lead to mold growth.
- It is typically installed with the shiny side facing the flooring and the fibrous side against the subfloor to optimize its moisture-blocking properties.
- For maximum effectiveness, adjacent sheets should overlap by at least two inches and be stapled or tacked in place every six to eight inches.
Noise Reduction and Wood-to-Wood Contact
Wood floors naturally expand and contract with changes in temperature and humidity. Without a buffer layer between the flooring and the subfloor, this movement can create squeaks and creaks as the planks rub against the underlying surface. Tar paper provides a cushioning layer that absorbs some of this friction, significantly reducing noise. As Charles Peterson of Connecticut Premier Hardwoods notes, rosin paper can also cut noise, but it does not provide the same moisture protection that tar paper offers. This dual benefit makes tar paper a superior choice for most installations.
Choosing Between Tar Paper and Other Underlayment Options
Not all underlayment materials are created equal, and the right choice depends on your specific project requirements. While tar paper has been a staple in the flooring industry for generations, modern alternatives such as foam underlayment, cork sheets, and synthetic moisture barriers offer different advantages.
| Underlayment Type | Moisture Protection | Noise Reduction | Best Use Case |
|---|---|---|---|
| Tar Paper (Asphalt-Saturated Felt) | Good | Good | Solid wood and engineered wood over wood subfloors |
| Rosin Paper | Poor | Moderate | Temporary protection, dust barrier during construction |
| Foam Underlayment | Poor to Moderate | Good | Laminate and floating floor installations |
| Cork Underlayment | Moderate | Excellent | Hardwood and tile, where soundproofing is a priority |
| Polyethylene Vapor Barrier | Excellent | Poor | Concrete subfloors with high moisture risk |
When to Use Rosin Paper Instead
If moisture is not a concern and you simply need a dust barrier and minor cushioning, rosin paper can serve the purpose at a lower cost. However, rosin paper provides negligible moisture protection and should never be used over concrete slabs or in below-grade installations. For projects where moisture is a potential issue, always choose tar paper or a purpose-engineered vapor barrier.
Synthetic Underlayment Alternatives
Synthetic underlayment products made from polypropylene or polyester offer superior tear resistance compared to traditional tar paper and are less messy to work with. However, they come at a higher cost. For more detail on selecting the right finish and underlayment, read our guide on prefinished versus unfinished hardwood flooring.
Installation Best Practices for Tar Paper Underlayment
Proper installation of tar paper is essential to realize its full benefits. Even the best underlayment material will underperform if installed incorrectly.
Preparing the Subfloor
Before laying down tar paper, the subfloor must be clean, dry, and level. Sweep or vacuum thoroughly to remove all debris and protruding nails. For concrete subfloors, ensure the slab has cured fully and test for moisture content. A moisture reading below three pounds per 1,000 square feet per 24 hours is generally acceptable for wood flooring installation.
- Sweep and vacuum the subfloor completely.
- Check for level using a six-foot straightedge; sand or fill low spots as needed.
- Acclimate the wood flooring in the room for at least 72 hours before installation.
- Roll out the tar paper across the subfloor in the direction perpendicular to the flooring planks.
- Overlap adjacent sheets by two to three inches and staple every six inches along the seams.
Laying the Tar Paper
Start at one end of the room and roll the tar paper out along the length of the subfloor. Allow each row to overlap the previous row by two to three inches. Secure the paper with staples every six to eight inches along the edges and every 12 inches in the field. Avoid over-perforating the paper with excessive fasteners.
Working Around Obstacles
When you encounter pipes, heating vents, or doorways, cut the tar paper to fit around them with a sharp utility knife. Allow an extra inch of material to wrap up slightly at the edges for added protection. In doorways, extend the tar paper into the adjoining room so that the underlayment remains continuous.
Troubleshooting Common Flooring Issues Related to Underlayment
Even with careful installation, flooring problems can arise. Many of these issues trace back to the underlayment layer. Recognizing the signs of underlayment failure and knowing how to address them can save you from costly repairs.
Squeaky Floors and Fixes
Squeaks are one of the most frequent complaints about wood flooring. While tar paper helps reduce friction noise, squeaks can still occur if the subfloor is not properly secured. Ensure every subfloor panel is screwed down firmly and that the tar paper is laid flat without wrinkles. For existing squeaky floors, walk across and mark the squeaky spots, then lubricate the joints with powdered graphite before resorting to invasive repairs. For a step-by-step approach, see our guide on how to cure squeaky floors.
Moisture Problems and Cupping
If your wood flooring boards are cupping upward at the edges, moisture imbalance is the likely culprit. Cupping indicates that the bottom of the board is wetter than the top. Check the subfloor for dampness and test the moisture content of both the flooring and the subfloor with a moisture meter.
- Run a dehumidifier in the room for several days to reduce ambient moisture.
- Ensure the crawlspace or basement below the floor is properly ventilated.
- If cupping is severe, affected boards may need to be removed and replaced after addressing the moisture source.
Adhesive Compatibility
Some flooring manufacturers recommend using a bead of urethane glue every 10 to 12 inches under the planks for additional stability. However, this approach can conflict with tar paper installation, as the glue needs direct contact with the subfloor. Always verify compatibility before beginning the installation. For those considering DIY restoration of older floors, our guide on refinishing ebonized oak flooring offers practical advice for reviving damaged wood surfaces.
When moisture migration is a concern and glue is required, contact the flooring manufacturer directly. They may recommend sealing the backs of the planks with a specialized coating. Some manufacturers produce foam underlayments with integrated vapor barriers that allow glue-down installation while still providing moisture protection. For more information on selecting the right materials, explore our resource on flooring types and material options.