Is Your Subfloor Hiding a Dirty Little Secret? The Truth About Tar Paper
You walk across your beautiful hardwood floors, and then you hear it—that persistent, annoying squeak. Or maybe you’ve noticed a strange draft coming up from the floorboards, or even worse, the tell-tale signs of moisture damage like cupping or buckling. These common household problems often point to a single, overlooked component deep beneath your feet: the subfloor.
Many homeowners never think about what lies between their finished flooring and the foundational joists of their home. Yet, this hidden space is critical to the longevity, stability, and comfort of your floors. For decades, one old-school material has been the go-to solution for many of these issues: tar paper.
But is this classic building material a relic of the past, or is it still a vital, cost-effective solution for protecting your flooring investment? The answer is more complex than you might think. Understanding the role of felt paper between subfloor layers is key to preventing a host of future problems.
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What Exactly Is Tar Paper and Why Is It Under Your Floor?
Tar paper, also known as asphalt felt or roofing felt, is a heavy-duty paper product impregnated with asphalt. This process makes it water-resistant, durable, and a staple in construction for over a century, primarily in roofing. However, its unique properties have made it a long-standing choice for flooring applications as well.
When used in flooring, it’s typically laid directly over the plywood or OSB subfloor before the finished flooring, like hardwood, is installed. It’s not just a random sheet of paper; it serves several distinct and important functions that contribute to the health and stability of your entire flooring system.
You’ll most commonly find it in two weights: #15 felt and #30 felt. The number refers to the weight per 100 square feet, with #30 being the thicker, heavier, and more durable option of the two. The choice between them often depends on the specific needs of the installation, especially the potential for moisture.
The #1 Problem Tar Paper Solves: Moisture Mayhem
The primary reason builders and flooring installers use tar paper is to act as a vapor retarder. It is not a complete vapor barrier like a plastic sheet, and that distinction is crucial. Wood is a natural material that needs to breathe, meaning it absorbs and releases moisture to acclimate to its environment.
A subfloor over a damp basement or a poorly ventilated crawlspace can constantly wick moisture upward. This moisture vapor can get absorbed by the underside of your expensive hardwood flooring, causing it to swell, cup, warp, and eventually fail. Tar paper creates a semi-permeable layer that slows down this moisture transfer, giving the wood a chance to adjust gradually without being overwhelmed.
By slowing, but not completely blocking, moisture movement, tar paper helps maintain a more stable equilibrium. This is why you should never use a full plastic vapor barrier under hardwood on a wood subfloor—it can trap moisture within the subfloor itself, leading to rot and mold. For floors over concrete, a different approach is needed, but for wood-on-wood installations, asphalt felt is a time-tested solution.
The Silent Treatment: Can Tar Paper Really Stop Floor Squeaks?
This is one of the most debated benefits of tar paper. Many installers swear by it, while others claim it does nothing for noise. The truth lies somewhere in the middle. Tar paper does not fix structural squeaks caused by loose subfloor panels or joists that are not properly secured.
However, it can significantly reduce or prevent minor squeaks caused by the friction of wood rubbing against wood. As the finished hardwood planks expand and contract with seasonal humidity changes, they can rub against the subfloor beneath them. The layer of asphalt-impregnated felt acts as a cushion and a slip sheet, providing a buffer that minimizes this direct contact and the annoying sounds that result.
Think of it as a gasket between two moving parts. While it’s not a cure-all for a noisy floor, installing it is an inexpensive insurance policy against one of the most common sources of floor squeaks. For older homes with unique subfloors, like a shiplap subfloor, this cushioning effect can be particularly beneficial.
Tar Paper vs. Modern Underlayments: An Honest Comparison
While tar paper is a classic, the market is now filled with modern underlayment options, from synthetic vapor barriers to foam and cork. Each has its own set of advantages and is suited for different applications. Understanding the differences is key to making the right choice for your project.
Tar paper remains a top contender for nail-down hardwood floors due to its cost-effectiveness and proven performance as a vapor retarder. Modern synthetic underlayments offer higher durability and are often easier to work with, but they come at a higher price point. Foam and rubber are excellent for sound dampening but are primarily used for floating floors (like laminate or LVP) and are unsuitable for nail-down installations.
| Underlayment Type | Primary Use | Moisture Protection | Sound Reduction | Cost |
|---|---|---|---|---|
| #15 Tar Paper (Felt) | Nail-down hardwood | Good (Vapor Retarder) | Minimal (Reduces friction squeaks) | Low |
| Rosin Paper | Nail-down hardwood | None | Minimal (Reduces friction squeaks) | Very Low |
| Synthetic Underlayment | Floating & some nail-down floors | Excellent (Vapor Barrier) | Moderate | Medium |
| Foam/Rubber Underlayment | Floating floors (Laminate/LVP) | Good (Often includes barrier) | Excellent | Medium to High |
| Cork Underlayment | Floating & glue-down floors | Fair (Needs separate barrier) | Excellent | High |
Step-by-Step Guide: How to Properly Install Tar Paper
Installing tar paper is a straightforward process, but attention to detail is key to its effectiveness. A sloppy installation can be worse than no installation at all. Follow these professional steps for a flawless result.
Step 1: Subfloor Preparation is Everything
Your underlayment is only as good as the subfloor beneath it. Before you unroll a single sheet, ensure the subfloor is clean, flat, and secure. Sweep and vacuum thoroughly to remove all dust, debris, and stray fasteners from previous flooring.
Walk the entire area, listening for squeaks and looking for movement. Drive screws into the floor joists to secure any loose panels. Use a long straightedge to check for high or low spots, sanding down high spots and using a leveling compound for dips greater than 3/16 of an inch over 10 feet.
Step 2: Choosing Your Weapon: #15 vs. #30 Felt
For most standard residential applications over a dry, climate-controlled space, #15 felt paper is sufficient. It’s easier to work with, less expensive, and provides adequate moisture retarding properties. It’s the go-to choice for the majority of hardwood installations.
If you are installing flooring over a potentially damp area, such as a crawlspace or an unconditioned basement, upgrading to the thicker #30 felt provides an extra layer of protection and durability. The added thickness offers a more robust defense against moisture vapor transmission.
Step 3: Rolling It Out and Securing It
Start along the longest wall, rolling out the tar paper parallel to the direction you plan to install your flooring. Overlap each subsequent row by at least 4 inches. This overlap is critical for creating a continuous shield against moisture.
Use a pneumatic or hammer tacker with 3/8-inch staples to secure the paper to the subfloor. Place staples every 6 to 8 inches along the seams and sparingly in the field (the middle of the sheet). The goal is to hold it flat and in place, not to perforate it excessively.
Step 4: Cutting and Fitting Around Obstacles
A sharp utility knife is your best friend for this part of the job. When you encounter floor vents, pipes, or complex corners, lay the paper over the obstacle and make careful relief cuts. Trim the paper neatly around the opening for a snug fit. For doorways, run the paper completely through the opening to ensure continuous coverage under the threshold.
Common Mistakes to Avoid (That Pros Never Make)
Even a seemingly simple job can go wrong. Avoid these common pitfalls to ensure your tar paper installation is effective and professional.
Ignoring Subfloor Prep: The most common error is laying paper over a dirty, uneven, or squeaky subfloor. Tar paper will not fix these underlying issues; it will only hide them temporarily.
Not Overlapping Seams: Leaving gaps between rows completely negates the moisture-retarding benefits. A 4-inch overlap is the professional standard and should not be skipped.
Using the Wrong Fasteners: Do not use long nails or screws that will create large holes. Short staples are all that is needed to hold the paper in place until the flooring is installed.
Treating It Like a Waterproof Barrier: Remember, tar paper is a vapor retarder, not a waterproof membrane. It will not protect your subfloor from a plumbing leak or a flood.
Is Tar Paper Safe? Addressing Health and VOC Concerns
A common concern with any asphalt-based product is the potential for off-gassing and volatile organic compounds (VOCs). While tar paper does have a distinct odor during installation, this typically dissipates quickly. Once it is installed and covered by the finished flooring, any emissions are minimal and generally considered safe.
It’s important to distinguish modern tar paper from older building materials. For instance, some vintage flooring products contained asbestos paper backing, which poses a serious health risk. Reputable, modern asphalt felt is manufactured to be a safe and stable product for residential use.
If you are particularly sensitive to smells, you can air out the rolls in a garage or ventilated space for a day before installation. Working with good ventilation during the installation process is also recommended.
The Verdict: Is Tar Paper Still a Smart Choice in 2025?
In an age of advanced synthetic materials, does this old-school product still have a place? The answer is a resounding yes. For nail-down solid hardwood flooring over a wooden subfloor, tar paper remains one of the most cost-effective and reliable options available.
Its ability to slow moisture vapor while allowing the subfloor assembly to breathe is a key advantage that many modern, impermeable barriers lack. It provides a proven, inexpensive solution to help prevent squeaks and protect your flooring from moisture damage. While synthetic options have their place, the performance-to-cost ratio of asphalt felt is hard to beat.
Ultimately, the decision to use tar paper comes down to a simple, time-tested principle: an ounce of prevention is worth a pound of cure. For a few extra dollars and a little bit of time, you create a protective layer that safeguards your much larger flooring investment for decades to come.
