For most roofing felt, the manufacturer’s instructions determine which face goes up. Many products are installed with the printed or marked side facing up, but there is no safe universal rule for every brand and type. Check the product label and installation guide before unrolling the felt. Correct orientation, overlap, fastening, and weather protection all matter: improperly installed underlayment can wrinkle, leak, or fail to provide the backup protection a roof needs.
The Short Answer: Check the Product Instructions
Roofing felt is a water-resistant underlayment installed between the roof deck and shingles or another roof covering. If the roll has a printed side, that side commonly faces up on products whose instructions call for it. The reverse face goes against the roof deck. However, products differ, and the printed side is not a reliable substitute for the manufacturer’s directions.
Some felt is not clearly marked, and different products may have different surface treatments or installation details. If a roll has no visible printing, inspect its packaging or technical data sheet for phrases such as “printed side up,” “install with the smooth side up,” or “either side may face up.” If the instructions are unavailable, contact the manufacturer rather than guessing.
Bottom line: Do not assume that the rough side, smooth side, or unprinted side always goes down. Follow the instructions for the specific product being installed.
Why Roofing Felt Has Different Sides
Roofing felt is generally made from a fibrous base saturated or coated with asphalt. Modern synthetic underlayments are different materials, even though they serve a similar role. Depending on the product, one face may carry printing, texture, a coating, or other features intended to help identify the product or support installation.
Texture can affect grip, and printed marks can help crews line up courses or identify the brand. But those features do not establish a universal orientation rule. A rough-looking face does not necessarily mean “up,” and a smooth face does not necessarily mean “down.” Surface appearance alone is not enough to identify the correct installation direction.
How To Identify the Correct Face
- Read the roll wrapper. Look for diagrams, arrows, orientation notes, and installation directions before removing the packaging.
- Check the manufacturer’s website. Search the exact product name or model number with “installation instructions.” Use the current document for that product, not a guide for a similar-looking roll.
- Look for markings on the felt. Repeating logos, lap lines, or directional arrows may help with placement. Follow any instruction that states which face must be exposed.
- Ask the supplier or manufacturer. Provide the product name, label information, or a clear photo of the roll. A roofing supplier may also be able to identify the material.
If the product’s instructions specify an orientation, that direction takes priority over general advice. If they state that either face can be installed upward, follow the remaining installation requirements, including the specified laps and fastening pattern.
What Roofing Felt Does—and Does Not Do
Roofing felt is a secondary water-shedding layer beneath the roof covering. It can help protect the roof deck if shingles are damaged, displaced, or exposed during construction. It also provides a layer between the deck and the finished roofing material. The exact performance depends on the product, roof design, installation, and local conditions.
Felt is not a replacement for shingles, flashing, or a properly designed roof drainage system. It should not be treated as a permanent exposed roof covering unless its manufacturer specifically permits that use. Prolonged exposure to sun, wind, rain, or foot traffic can damage some underlayments. Check the product’s exposure limits and install the finished roof promptly.
Proper Installation Matters as Much as Orientation
Even correctly oriented roofing felt can leak if it is installed with poor overlaps, loose edges, or unsealed penetrations. The details vary by product and roof configuration, so the manufacturer’s instructions and applicable building code should guide the work.
Start at the Eaves
Underlayment is generally installed in horizontal courses, beginning at the eaves and progressing toward the ridge. This arrangement lets upper courses overlap lower ones so water can drain down and over the laps. The first course should be placed and aligned according to the product instructions and roof details.
Use the Required Overlaps
Roofing felt is installed with both horizontal and end laps. The required width can vary with the product, roof slope, exposure, and local code. Do not rely on a single overlap measurement found in a general online guide. Follow the roll instructions and applicable code for the specific installation.
Keep Courses Straight and Flat
Pull the felt snug without stretching or tearing it, and avoid wrinkles, buckles, or folds. Uneven underlayment can interfere with shingle installation and create places where water may collect or travel beneath the roof covering. Align courses with the manufacturer’s markings when provided.
Fasten It Correctly
Use the fasteners and fastening pattern specified by the manufacturer and code. The correct fastener type and placement help keep the material secure against wind and prevent avoidable damage. Fastener requirements may change based on the roof slope, local wind conditions, and the underlayment system.
Protect Valleys, Edges, and Penetrations
Roof valleys, eaves, rakes, chimneys, vents, and other transitions need careful detailing. These areas may require additional underlayment, flashing, or an ice barrier, depending on the roof design and local requirements. Felt alone does not make a poorly flashed joint watertight.
Roof Slope, Weather, and Code Requirements
Roof slope affects how underlayment must be installed. Low-slope roofs may need different materials or special application details because water drains more slowly. In the United States, the International Residential Code addresses underlayment for asphalt shingles and requires installation consistent with applicable provisions and manufacturer instructions. Local jurisdictions may adopt different code editions or amendments.
Cold-climate areas may require ice barriers at eaves and other locations, while wind-prone areas may have additional fastening requirements. These rules are not identical across the country. Before work begins, check with the local building department or a qualified roofing professional about permits, adopted codes, and any region-specific requirements.
Weather also matters. Wet, icy, or windy conditions can make underlayment slippery, difficult to handle, or unsafe to install. Some products have temperature or exposure limitations. The product documentation should state how long the material can remain uncovered and how it should be protected if the roofing work is delayed.
Common Roofing Felt Orientation Mistakes
- Assuming every product is installed the same way. Felt and synthetic underlayments can have different instructions, even when their rolls look similar.
- Using texture as the only guide. A rough or smooth surface does not prove which face belongs up.
- Ignoring printed directions. If the manufacturer labels one side as the top, install it as directed.
- Reversing the overlap direction. Courses should be layered so water sheds over the lower course, not behind it.
- Leaving the underlayment exposed too long. Exposure limits vary, and weather can damage material before shingles are installed.
- Skipping roof-safety precautions. Roofing is a fall-risk job. A dry-looking surface can still be slick, and felt may not provide secure footing.
Roofing Felt vs. Synthetic Underlayment
Traditional asphalt-saturated felt and synthetic underlayment are not interchangeable in every situation. Synthetic products often use woven or nonwoven polymer layers and may have textured surfaces, printed layout lines, or specific directional requirements. Some are designed to resist tearing or tolerate longer exposure than felt, but performance varies by brand and model.
Do not transfer instructions from one material to another. A rule that applies to one felt product may not apply to a synthetic roll, and vice versa. Confirm the exact product type before installation, particularly when matching the underlayment to a roofing system warranty or building-code requirement.
| Question | What to Check |
|---|---|
| Which face goes up? | Product label and manufacturer installation guide |
| How much should courses overlap? | Product instructions, roof slope, and local code |
| How long can it remain uncovered? | Exposure limit stated by the manufacturer |
| Are extra layers required? | Roof details, climate, code, and roofing-system design |
When To Call a Roofing Professional
Professional help is sensible when the roof is steep, high, damaged, or difficult to access; when the product cannot be identified; or when the roof includes complex valleys, low slopes, or multiple penetrations. A roofer can assess the roof deck, select a compatible underlayment, and account for local code and weather requirements.
Roof work presents a serious fall hazard. OSHA identifies falls as a major construction hazard and requires appropriate fall protection in covered work situations. Homeowners should not climb onto a roof without proper training, equipment, and safe access. A professional can also confirm whether damaged or wet decking needs repair before new underlayment is installed.
Reliable Sources for Installation Guidance
For product-specific direction, use the instructions published by the underlayment manufacturer. For code questions, consult the locally adopted building code and the local building department. The International Code Council publishes the International Residential Code, while OSHA provides construction fall-protection requirements. These sources are more dependable than generic advice about which side of roofing felt goes down.
In practical terms, the marked or printed side often faces up when the product’s instructions say so—but the exact roll’s installation guide is the deciding authority. Confirm the orientation first, then install the felt with the required course direction, laps, fastening, and weather protection.