Tar Paper Roof: What It Is and How to Install

Old-timers still call it tar paper, and the name causes plenty of confusion because there is no tar involved and it is not a roof by itself. A tar paper roof really means an asphalt-saturated felt underlayment installed beneath the shingles, the black paper you see rolled out on bare decking before the finished roof goes on. It is the same material generations of roofers have used as the secondary water barrier under asphalt shingles. I have installed miles of it and torn off decades-old felt that was still shedding water long after the shingles above it gave out. Knowing what tar paper is, and what it is not, keeps you from making a costly mistake on your roof.

This guide explains what a tar paper roof actually is, the weights and coverage you need, and how to roll it out correctly by hand.

What Tar Paper Really Is

Tar paper is a base felt mat, historically made of recycled paper or fiberglass, saturated with asphalt to make it water-resistant. The asphalt is what makes it black and gives it the tarry smell people associate with the name. It is a roofing underlayment: a barrier that goes between the wood decking and the shingles, not a finished roof surface on its own.

People sometimes think a tar paper roof is a standalone waterproof roof. It is not. Left exposed, felt degrades in UV within weeks to a few months, wrinkles, and eventually cracks. It is designed to be covered by shingles, which are the actual weather surface. Felt only serves as a temporary cover during construction and a permanent backup layer afterward.

What It Does Under Your Shingles

Felt underlayment earns its keep in three ways. It provides secondary waterproofing, catching any wind-driven rain that gets past the shingles and directing it down to the drip edge. It protects the decking during the days between tear-off and shingle install, keeping the plywood dry. And it acts as a separator, stopping the wood’s resins from bleeding into the shingles and preventing the shingles from bonding to and mirroring the deck surface.

Building code requires underlayment under asphalt shingles, and shingle manufacturers generally void their warranty if you nail shingles straight to bare decking. Whatever you call it, the layer is not optional.

15 lb vs 30 lb: Which Weight to Use

Tar paper comes in two common weights, named for their historical weight per square (100 square feet):

• 15 lb felt: Lighter and thinner, covering about 400 square feet per roll. Cheaper, adequate for standard shingle jobs in mild climates, but tears easily and wrinkles in heat.
• 30 lb felt: Heavier and tougher, covering about 200 square feet per roll. It lies flatter, resists foot traffic and tearing, and holds up better if the roof sits exposed a few days before shingling.

For most reshingle work I reach for 30 lb because it wrinkles less on a hot deck and resists tearing around nails. On low-slope areas and in windy regions, the extra body is worth the added cost. Modern synthetic underlayments outperform both and cover 1,000 square feet per roll, but true asphalt felt is still cheap, familiar, and warranty-approved for most shingles.

How Much You Need

Order by roof squares and account for overlap. Felt laps 2 inches on horizontal seams and 4 to 6 inches at end laps, so real coverage runs a little under the nominal roll size:

• 15 lb: roughly 3.5 to 4 squares of coverage per roll
• 30 lb: roughly 1.8 to 2 squares of coverage per roll

Add 10 to 15 percent for waste at valleys, hips, and cuts. For a 24-square roof, plan on about seven rolls of 15 lb or thirteen rolls of 30 lb, plus separate ice-and-water shield for the eaves and valleys.

Tools and Prep

Before rolling felt, get the deck ready. Sweep it clean of debris and old nails, replace any rotten or spongy decking, and install the drip edge at the eaves first. You will need:

• Roofing nails with plastic caps or a hammer-tacker with cap staples, never bare staples
• A utility knife with hook blades and a straightedge
• A chalk line to keep courses straight
• Roof jacks and a harness on anything steeper than about 6/12

Wait for dry weather. Wet felt is dangerously slick, and rolling it over damp decking traps moisture under the shingles.

Step-by-Step Install

Work bottom to top so every course sheds over the one below:

1. Install any self-adhering ice-and-water shield along the eaves and in the valleys first, per code in cold climates.
2. Snap a chalk line for the bottom felt course so it runs straight along the eave, edge flush to the drip edge.
3. Roll out the first course, keeping it flat and wrinkle-free, and fasten with cap nails or cap staples about 12 inches on center in the field and 6 inches along the laps.
4. Overlap each successive course at least 2 inches over the one below; stagger and overlap end laps 4 to 6 inches so seams do not stack.
5. Run felt up and over ridges and hips, lapping both sides so water cannot drive into the seam.
6. Cut in around vents, chimneys, and walls, integrating the felt with the flashing so metal laps over felt at the top and felt laps over metal at the bottom.

Keep the sheet taut and flat. Wrinkles telegraph through the finished shingles as raised lines you will see from the ground on a hot afternoon.

Common Mistakes to Avoid

The errors I see repeatedly: fastening felt with bare staples that back out and let it flap loose, leaving felt exposed for weeks until it wrinkles and cracks, reversing the laps so water runs into seams instead of over them, and skipping ice-and-water shield at the eaves in snow country. Another is treating tar paper as a finished roof and leaving it uncovered for a season; it will not survive.

Done right, felt underlayment is the quiet layer that keeps your house dry when a shingle blows off in a storm. Roll it flat, lap it correctly bottom to top, cap-fasten it, and cover it promptly with shingles, and your tar paper will still be doing its job long after the finished roof needs its next replacement.

Tar Paper and Roof Slope

How you install tar paper depends on the pitch of your roof. On standard slopes of 4/12 and steeper, a single layer of felt with normal 2-inch head laps is sufficient under asphalt shingles. On low slopes between 2/12 and 4/12, both code and shingle manufacturers require a doubled underlayment, each course half-lapped so the felt is effectively two layers thick across the whole roof, because water drains slowly on a shallow pitch and lingers longer at every seam.

Below 2/12, standard shingles and ordinary felt are not enough; that low pitch calls for a membrane roof or a fully self-adhered underlayment system. Matching the felt approach to the slope is essential, because a shallow roof with only single-lapped felt will leak at the laps where water sits instead of running off.

Tar Paper vs. Synthetic Underlayment

Modern synthetic underlayments have largely replaced traditional felt on quality jobs, and it helps to know why. A single synthetic roll covers about 1,000 square feet versus 200 to 400 for felt, weighs far less, will not absorb water or rot, resists tearing, and can stay exposed for months rather than weeks. Many synthetics also have walkable, slip-resistant surfaces and printed nail lines that speed up install.

Tar paper still holds a few advantages: it is inexpensive, familiar to every roofer, warranty-approved for essentially all asphalt shingles, and suitable under hot-applied and torch-applied systems where some synthetics are not rated. If budget is tight or a specific warranty calls for felt, it remains a perfectly sound choice. For most reshingle jobs where you want the easiest, most durable underlayment, synthetic wins; where cost and tradition rule, tar paper still does the job it always has.

Handling and Storing Tar Paper

Keep felt rolls dry and off the ground until install day. Felt that soaks up rain gets heavy and wrinkles the instant you unroll it on a warm deck. Store rolls upright under cover, and let very cold felt warm slightly before installing so it lies flat instead of cracking. Plan your courses to minimize waste at valleys and hips, and cut cleanly with a hook blade against a straightedge.

Only roll out as much felt as you can fasten and cover with shingles in a reasonable window. Leaving a large area of bare tar paper exposed invites a surprise storm to wrinkle, tear, and degrade it before the shingles ever go on, which defeats the purpose of installing it in the first place.

The Bottom Line on Tar Paper Roofs

A “tar paper roof” is really asphalt felt underlayment doing its quiet, critical work beneath the shingles, secondary waterproofing, deck protection during construction, and separation between wood and shingle. Choose the right weight for your climate and slope, lay ice-and-water shield at the eaves and valleys in cold country, roll the felt bottom to top with proper laps, cap-fasten it flat and wrinkle-free, and cover it promptly. Do that, and the humble black paper keeps your house dry even the day a shingle blows off in a storm, long after the finished roof above it has come and gone.