How Do I Install Tar Paper on a Roof the Right Way?

Have you ever worried that a mistake with tar paper could lead to a costly leak? I’ve fixed plenty of roofs where that was the exact problem.

Getting this layer wrong undermines your entire roof. Doing it properly is your first defense against water damage.

I’ll cover the essential tools, the step-by-step rolling and fastening process, and how to seal the overlaps for total protection.

What Exactly is Tar Paper and Where Does It Go?

Tar paper is asphalt-saturated felt. Think of it as a tough raincoat for your roof deck, the wooden boards under your shingles.

This layer is a critical backup system that catches wind-driven rain or melting ice before it soaks into your roof deck. It prevents rot and protects the structure of your home. On many repairs, I’ve seen tar paper hold back water for weeks after a shingle blew off, saving the homeowner from major interior damage.

Let’s clear up common confusions. Tar paper is a rolled underlayment you nail down. A temporary roof tarp is a plastic sheet tied down for emergencies. Liquid roofing tar is a gooey sealant for patches. They are not the same thing—and especially not a temporary roof substitute.

You’ll buy it by weight. #15 and #30 are standard. The number is the weight in pounds for a 100-square-foot roll. #30 felt is nearly twice as thick as #15, offering better durability and puncture resistance for a longer-lasting job. For most homes, I recommend #30.

Safety and Real Talk: When This Job is For Pros Only

Working on a roof is inherently risky. The dangers are real: a steep pitch can send you sliding, power lines are often nearby, and a fall from any height can be fatal.

If you choose to proceed, proper gear is not optional. You must use a fall-arrest harness that is securely anchored to a roof-rated point, install roof jacks and planks for a safe footing platform, and wear shoes with aggressive, non-slip soles. My crew’s rule is simple: no anchor, no roof.

Be honest with yourself. Do not attempt this installation if:

• Your roof slope is steeper than a 6/12 pitch (a 6-inch rise for every 12 inches horizontal).
• The roof has complex features like multiple valleys, dormers, or a very high peak.
• The weather is wet, windy, or excessively hot.
• You have any doubt about your ability to work safely at height.

Hiring a licensed, insured roofing professional is the mark of a responsible homeowner. I’ve been called to redo more than one DIY underlayment job where the felt was installed wrong, leading to leaks. Getting it right the first time with a pro saves money and worry. If you’re weighing DIY roof repair versus hiring a pro, a quick comparison can help. A short guide later in this article will show when DIY makes sense and when to call in a pro.

Tools and Materials: Your Roofing Day Toolkit

Before you climb the ladder, get your gear in order. Having everything on the roof with you saves time and frustration. This is the same kit I’ve used on countless re-roofs.

Here is your essential tool list:

• Hammer (a roofing hatchet works even better)
• Roofing nails or plastic cap nails
• Sharp utility knife with extra blades
• Chalk line reel
• Tape measure

For materials, you will need:

• Rolls of tar paper (felt underlayment)
• Metal drip edge for the eaves and rakes
• Ice and water shield for eaves, valleys, and penetrations

This brings up a common question I hear: can you nail a tarp to the roof? The answer highlights the right way to secure underlayment. For a temporary storm tarp, you use wide, flat boards to sandwich and secure the edges, never nailing directly through the tarp into the deck. That creates holes. For permanent tar paper, you nail it directly. You place nails with large heads or plastic caps in a specific pattern to hold it flat and tight without tearing.

Store your tar paper rolls lying flat in a dry place. A damp garage floor can make the paper stick together or become brittle. You want it pliable for a smooth installation.

Choosing the Right Tar Paper and Fasteners

Not all tar paper is the same. The number, like #15 or #30, refers to its weight per 100 square feet. Thicker paper offers more protection.

#15 felt is your standard, lighter-weight option. I’ve used it on simple, steep-pitch roofs in drier climates where the primary job is to protect the deck during installation. It’s easier to handle but can tear more easily in the wind.

#30 felt is heavier and more durable. I recommend it for lower-pitched roofs or in areas with frequent rain. It provides a better secondary water barrier if wind-driven rain gets under your shingles. Think of it like the difference between a rain jacket and a heavy-duty poncho.

Your nails are just as important as the paper. Standard roofing nails with large heads work, but plastic cap nails are often superior. The wide plastic cap grips the felt over a larger area. This holds the paper flatter and resists tearing from wind uplift much better than a standard nail head. Nail length also matters, especially across different roofing materials. Different roofing materials—shingles, metal, tile, or built-up roofs—call for different nail lengths to ensure proper anchoring and wind resistance.

Always check your local building codes before you buy materials. Many areas now mandate specific underlayment types or weights, especially for roof slopes below a certain pitch. Following code isn’t just about legality; it’s a blueprint for a durable, safe roof.

Prepping the Roof Deck: Don’t Skip This Step

Think of your roof deck like the skin under a bandage. If it’s not clean and healthy, nothing you put on top will work right. I’ve spent whole days fixing leaks that started because a crew skipped this step.

Before you touch a roll of tar paper, walk the entire deck. Use this checklist. Your deck must be clean, dry, smooth, and structurally sound.

• Clean means zero debris. Sweep off all sawdust, old nails, and grit. A tiny nail shard can puncture the paper the first time you walk on it.
• Dry is non-negotiable. Check for morning dew or damp spots from a recent rain. Paper sticks to moisture, not wood.
• Smooth feels flat under your hand. Sand down any splintered plywood edges. A rough deck creates air pockets where the paper can’t seal.
• Structurally sound means no flex or soft spots. Jump lightly on suspect areas. If it gives or sounds hollow, the wood underneath is compromised.

When you find a soft spot, that’s rotten plywood or OSB. You must replace it now. Cut out the damaged section with a circular saw. Use a new piece of wood that matches the thickness of your existing deck. Covering rotten wood with tar paper is like putting a new floor over a termite-infested joist, the problem only gets worse.

With a solid deck, your next move is the drip edge along the eaves. Install this metal flashing before any tar paper goes down. Nail it directly to the deck. The tar paper will later lap over the top of it. This order is critical. Installing the eave drip edge first creates a guide that channels water safely over the paper and into your gutters.

On a job years ago, we papered first to save time. We had to notch the paper to fit the drip edge later. That house had a chronic leak at the eaves within two years. The water had a path behind the flashing.

Let me be blunt. Applying tar paper to a dirty or damp deck is a guaranteed future problem. The asphalt won’t bond. Trapped moisture will work its way into the wood. You’ll see mold stains on your ceilings long before the shingles fail. Always wait for a dry day and sweep twice.

The Main Event: Step-by-Step Tar Paper Installation

Follow these steps in order for a solid installation. Rushing this job always costs more time later.

Step 1: Starting at the Eaves and Rolling it Out

Begin at the bottom edge of your roof, the eave. Position the entire roll so it unrolls parallel to the edge.

Roll out your first full course across the entire width of the roof. Let it overhang the metal drip edge by about a quarter of an inch. This directs any water into the gutter. Keep a quick note of the overhang you set for reference in the gutter layout. Accurate roof gutter overhang measurements will guide the next steps.

Snap a chalk line on the sheathing along the top edge of this first course to guide your next row. If your underlayment is crooked, your shingles will be crooked too. I’ve seen crews spend hours fighting a crooked starter course because they skipped this line.

Step 2: Securing the Paper and Overlapping Seams

Lay the paper flat before you nail. Use cap nails or plastic-cap staples designed for underlayment. Start securing it in the center and work outwards to smooth out wrinkles.

Follow this nailing pattern:

• Place fasteners every 12 to 18 inches along the edges.
• Add a row of fasteners down the center of the roll.
• Set the nail head flush. Do not over-drive and tear the paper.

Now for the most critical part: the overlaps. This is the primary water-shedding system before the shingles go on.

• Side Laps: Where two rolls meet side-to-side, overlap them by at least 2 inches.
• Head Laps: Where one course meets the course below it, overlap by a minimum of 6 inches.

An improper head lap is where most leaks start, because it creates a direct path for driven rain or melting ice. Always make sure the upper layer overlaps the lower one, like shingles. The overlap must face downhill so water flows over it, not under it.

Step 3: Working Up the Roof to the Ridge

Use your chalk line to align the top of each new course. Roll, align, and secure. Repeat this process all the way to the ridge.

Manage your materials carefully. A full roll is heavy and can be awkward. Unroll only what you are ready to nail down immediately. Keep your work area clear of loose material, offcuts, and nail strips. A trip on a roof is serious.

Temperature matters. On a hot, sunny day, the tar can get soft and sticky. It can glue itself to the roof deck or to the back of the roll above it, making it very hard to handle. If you can, do this work in the cooler morning hours to save your back and your patience. On one scorching July job, we had to mist the deck with water just to get the paper to slide into position.

When you reach the ridge, run the final course over the peak. You will trim it later when you apply the cap shingles. For now, your roof should be covered in a continuous, shingle-lapped blanket.

Critical Leak Points: Sealing Valleys, Vents, and Chimneys

Valleys, vent pipes, and chimneys are where most roofs fail first. I have patched hundreds of leaks, and nearly all started in one of these spots.

Standard tar paper sheds water, but it is not waterproof. In a valley, water rushes down like a river. Around a pipe or chimney, wind can drive rain sideways under the shingles. Tar paper alone cannot stop that.

You need a self-adhering waterproof membrane, often called ice and water shield, for these critical areas. Think of tar paper as a sturdy work shirt. It handles daily wear. The ice and water shield is the waterproof jacket you put on over it when a storm hits.

Securing Valleys and Roof Penetrations

Applying the membrane correctly makes all the difference. Here is how we do it on my crew.

Start with a clean, dry deck. Sweep off all dust and debris. Any grit under the membrane can create a tiny hole for water to enter.

For open valleys, apply the ice and water shield like this:

1. Roll out a 3-foot-wide strip down the center of the valley. Start at the bottom edge of the roof.
2. Press it firmly onto the deck. The adhesive backing sticks best when the roof is warm.
3. Overlap each successive course by at least 6 inches as you work up the roof.

For plumbing vents and pipes:

1. Cut a square of membrane large enough to extend 6 inches up the pipe and 6 inches out on all sides.
2. Slice a small ‘X’ in the center of the square.
3. Slide the membrane up the pipe so the flaps lay flat on the roof deck. Press it down firmly.

Next, roll your tar paper right over the installed membrane. The tar paper is your secondary barrier. When you get to a pipe, cut a neat, tight slice in the tar paper to fit around it. Do not just poke a hole. I learned this the hard way on an old bungalow job where a ragged cut let in moisture for years.

Chimneys are more complex. A brick chimney needs a cricket, or saddle. This is a small peaked structure built behind the chimney to divert water around it.

The underlayment must integrate with the step flashing on the chimney sides. First, install ice and water shield on the deck around the base. Then, your tar paper layers should lap over the top edge of each piece of step flashing as you work up the chimney. This directs any water that gets behind the siding onto the underlayment and down the roof.

Why “How to Apply Roofing Tar” Isn’t the Answer Here

Many DIYers search for “how to apply roof tar” thinking it will seal their underlayment. That is a mistake.

Roofing tar or mastic is for emergency, temporary patches on finished shingles. I keep a can in my truck for quick fixes after storm damage. You should never use tar to glue down or seal the seams of your tar paper underlayment.

Tar and mastic dry out. They get hard and brittle over time. When your roof deck expands and contracts with temperature changes, that hardened tar will crack. Once it cracks, it is no longer a seal. It is just a mess to scrape off later.

A self-adhering membrane stays pliable for decades. It seals around nail holes and moves with the roof. That is the permanent protection you need.

Tar Paper in Context: How It Compares to Modern Underlayments

Let’s be clear. For decades, tar paper (also called felt paper or asphalt-saturated felt) was the only option. I’ve rolled out miles of it. Today, you have a choice: traditional #15 or #30 felt, or modern synthetic underlayment.

Think of it like a rain jacket. Tar paper is a reliable, old-school waxed canvas jacket. A synthetic underlayment is a modern, high-tech Gore-Tex shell. Both keep you dry, but they perform differently.

The Core Differences

Synthetic underlayment is usually made from woven polypropylene or polyester. It’s tougher. It won’t tear as easily when you’re walking on it, especially if it gets damp from morning dew. Compared with traditional felt underlayment, synthetic options often last longer and resist tearing. This makes the choice between synthetic and traditional underlayments a key point when planning roof projects. Synthetic is significantly stronger, lighter to carry up a ladder, and often has better slip resistance, which is a major safety plus for anyone on the roof.

The trade-off is cost. Roll for roll, synthetic is more expensive. But here’s my take from pricing hundreds of jobs: the material cost difference is small compared to the total project. The benefits in durability and crew safety during installation are usually worth it.

Being Honest About Tar Paper’s Limits

I still use tar paper for certain repairs or when a homeowner specifically requests it. But you should know its weaknesses. Tar paper becomes brittle and can degrade quickly when exposed to UV light for extended periods, like if shingle installation is delayed. It also absorbs moisture. When it’s wet, it’s much more prone to tearing underfoot, which can compromise your secondary water barrier before the shingles even go on.

We always planned jobs around the weather when using felt. If rain was possible, we worked faster or used synthetic. You don’t have that same panic with modern materials.

Installation is What Makes It Watertight

Here’s the truth that applies to any underlayment. A perfectly installed layer of tar paper will outperform a poorly installed layer of the most expensive synthetic every single time. The material is just one part of the system. Proper overlap, correct fastening, and sealing at critical points like valleys and eaves are what create a true secondary shield. A fancy underlayment with gaps is just a leak waiting to happen.

On my crews, I drilled this in: it doesn’t matter what you’re rolling out if you’re not laying it down right. The fundamentals of keeping water out never change.

How This Ties to Tile and Other Roofs

You might wonder how this relates to a question like “how do you tarp a tile roof” for emergency repairs. The principle is identical. Whether it’s felt, synthetic, or a temporary tarp, the goal is to shed water by creating a continuous, overlapping barrier that directs flow down and off the roof. The core concept of shingling layers from the eave up is universal, but the fastening method changes based on the roof deck and final roofing material.

For a tile roof, you’d use a specific high-strength underlayment and often nail it differently to accommodate the battens. But the mindset-overlap generously, secure it well, protect the edges-is the same wisdom that applies to installing tar paper under asphalt shingles.

Common Questions

What’s the biggest safety mistake DIYers make up on the roof?

Not using a properly anchored fall-arrest system. They rely on luck and shoe grip instead of a secured harness, which is the only thing that stops a fatal fall.

How do I keep the tar paper flat and avoid wrinkles?

Always start fastening from the center of the roll and work outwards to smooth it down. Before you nail, ensure the deck is clean and walk the paper into place to eliminate any bulges or air pockets.

What’s the most common error around vents or chimneys that causes leaks?

Cutting the tar paper too close to the penetration, leaving no material to integrate with the flashing on the roof. You must lap the paper properly over the base flashing or membrane to create a shingled water path down the roof.

Securing Your Roof’s First Line of Defense

Get the overlap right and keep everything nail-straight; doing these two things consistently turns tar paper into a reliable shield for your home. I’ve seen roofs withstand brutal storms because the crew took that extra minute to measure and secure each sheet properly.

Treat your roof as a long-term investment that demands your attentive care and a safety-first mindset for any upkeep. You build lasting expertise by using resources like our detailed Roof Care, All Types of Roof Guide, Care, and Maintenance articles for trustworthy guidance. Knowing roof repair safety practices is crucial when handling any maintenance or repair tasks.