Roofing decisions hinge on details like underlayment choice. This article compares Roof Felt Paper 15 Vs 30 to explain differences, performance, installation considerations, cost, and code implications for U.S. homeowners and contractors. Readers will learn which felt suits common roofing scenarios and how each option impacts long-term roof protection.
| Characteristic | 15# Felt | 30# Felt |
|---|---|---|
| Weight Per 100 Sq Ft | ~15 Pounds | ~30 Pounds |
| Thickness | Thinner, Lighter | Thicker, More Durable |
| Durability | Moderate | Higher Resistance To Tears |
| Cost | Lower | Higher |
| Typical Use | New Construction, Low-Risk | Steeper Roofs, High-Wind Areas, Re-roofing |
What Is Roofing Felt And Why It Matters
Roofing felt, often called tar paper or underlayment, is a protective layer installed over the roof deck before shingles. It serves as a temporary weather barrier during installation and an additional moisture shield for the finished roof. Choosing between 15 and 30-pound felt affects durability, tear resistance, and water protection, so the selection matters for roof lifespan and warranty compliance.
Construction And Material Differences
Both 15# and 30# felt are made from cellulose or fiberglass mats saturated with asphalt, sometimes with a mineral surface. The number refers to the approximate weight per 100 square feet in older measurement conventions. 30# felt is heavier and thicker, offering greater tear resistance and durability than 15# felt.
Weight, Thickness, And Composition
15# felt is lighter and easier to handle but is more prone to wrinkling and tears, particularly on steep slopes or windy days. 30# felt adds mass that resists blistering and punctures. Modern synthetic underlayments complicate the comparison, but among traditional felts, the heavier product remains stronger.
Performance: Water Resistance And Durability
Roof felt’s primary job is temporary weather protection and secondary defense against water infiltration after shingles fail. 30# felt provides superior protection against wind-driven rain, ice dams, and foot traffic during installation compared to 15# felt, reducing the risk of leaks during adverse weather events.
Wind And Tear Resistance
On exposed sites or during reroofing when crews walk the deck, the thicker 30# felt resists tearing and is less likely to shift under wind. For low-slope roofs or sheltered installations, 15# felt may suffice but offers less margin for error in harsh conditions.
Installation Considerations And Handling
Installers note that 15# felt is lighter and easier to unroll, especially for single-person crews. However, because it tears more readily, it may require more careful handling. 30# felt demands more effort to manipulate but typically reduces rework from tears and wind damage.
Nailing, Overlaps, And Seaming
Nail pattern and overlap recommendations are similar for both weights, but 30# felt tolerates tighter schedules because it better withstands temporary exposure. In high-wind zones, manufacturers and building codes often require specific overlaps or a higher weight underlayment for safety.
Code Requirements And Manufacturer Warranties
Building codes and shingle manufacturers sometimes specify minimum underlayment standards. Local codes may require heavier underlayment in regions with severe weather. Using the correct felt—often 30# or an approved synthetic—is critical to maintaining shingle warranties and code compliance.
Insurance And Local Jurisdictions
Insurance providers may ask about roofing materials after weather events. Some jurisdictions prefer or mandate higher performance underlayments in hurricane-prone or cold-climate areas to mitigate claims. Always verify local code and warranty documents before deciding between 15# and 30# felt.
Cost Comparison And Lifecycle Value
15# felt is typically less expensive up front, offering cost savings for large projects. However, 30# felt costs more but may lower long-term repair and maintenance expenses due to fewer installation-related leaks and better durability. Lifecycle value often favors 30# felt in exposed or high-traffic roofing scenarios.
Material And Labor Trade-Offs
Because 15# felt is easier to handle, labor time may be slightly reduced, but increased risk of damage can negate initial savings. 30# felt may increase hauling and handling effort, but its toughness often shortens corrective work and improves overall roof resilience.
When To Choose 15# Felt
15# felt fits well for sheltered roofs, mild climates, and new construction where roofs will be covered quickly. It remains cost-effective for short-term protection during fast installations and for structures with low exposure to wind-driven rain.
Typical Use Cases
- New roofs on homes in low-wind, low-precipitation areas
- Quick installations where shingles follow immediately
- Situations prioritizing minimal weight on fragile structures
When To Choose 30# Felt
30# felt is recommended for steep-slope roofs, high-wind regions, reroofing projects, or when work may leave the deck exposed for longer periods. It is the better choice where durability and tear resistance are priorities.
Typical Use Cases
- Reroofing where the deck may be walked on during removal
- Coastal, mountain, or storm-prone regions
- Applications requiring higher margin for installer error
Synthetic Underlayments: An Alternative To Consider
Synthetic underlayments have gained popularity for their lighter weight, superior water-shedding, and longer UV exposure life compared to traditional felts. They often outperform both 15# and 30# felt in tear resistance and slip resistance. For many modern projects, synthetics offer a balanced option with longer exposure limits and better performance, though cost and compatibility with certain shingles must be reviewed.
Advantages And Trade-Offs
Synthetics resist rot and absorb less water than asphalt-saturated felts, and they come with manufacturer exposure limits. However, installation technique differences and higher initial cost are trade-offs to consider when evaluating 15# vs 30# felt alternatives.
Environmental And Safety Considerations
Felt is petroleum-based and disposal adds to waste streams. Synthetics may offer recyclability advantages depending on product type. During installation, heavier felt can present manual handling risks; appropriate PPE and team lifting techniques reduce strain. Selecting the underlayment should account for environmental impact, installer safety, and disposal logistics.
Practical Buying And Installation Tips
Select underlayment based on climate, roof exposure, and project timeline. Read shingle manufacturer requirements, consult local building codes, and consider synthetic options. Always store rolls flat and dry, follow overlap and nailing instructions, and avoid long-term UV exposure for felt products.
- Verify code and warranty requirements before purchase.
- Order a little extra to account for waste and overlaps.
- Use non-slip footwear and fall protection when working on steeper roofs.
- Replace damaged felt sections immediately during installation.
Cost Estimates And Material Quantities
For budgeting, a roll of 15# felt covers about 400 square feet and weighs roughly 60 pounds per roll, while 30# felt also covers about 200 square feet per roll but is heavier per coverage unit. Prices vary by region and brand. Estimators should compare cost per square foot and factor in labor, waste, and potential rework from material failures.
| Item | Coverage | Typical Weight Per Roll | Typical Price Range |
|---|---|---|---|
| 15# Felt Roll | ~400 Sq Ft | ~40–60 Lbs | $10–$25 Per Roll |
| 30# Felt Roll | ~200 Sq Ft | ~60–90 Lbs | $15–$40 Per Roll |
Frequently Asked Questions
Does 30# Felt Prevent Leaks Better Than 15#?
30# felt offers greater tear resistance and temporary water protection, reducing leak risk during installation and in some failure scenarios. It does not make a roof waterproof but improves the roof’s secondary defense.
Are There Situations Where 15# Is Required?
Some manufacturers or local practices still accept 15# felt for specific applications, but modern codes and warranties increasingly favor heavier or synthetic underlayments. Always check project-specific requirements before selection.
Can Synthetics Replace Felt Entirely?
Synthetic underlayments are valid replacements in many cases and often exceed felt performance metrics. Compatibility with shingle warranties and cost should guide the decision. Many contractors now prefer synthetics for exposure durability and safety.
Key Takeaways For Decision Makers
Choosing between 15# and 30# felt depends on exposure, code, cost, and installation timeline. 30# felt generally provides better durability and protection; 15# felt remains a budget choice for sheltered, quick projects. Evaluate synthetic underlayments as a modern alternative in many U.S. roofing applications.
For best results, consult local building codes, follow shingle manufacturer requirements, and discuss conditions with an experienced roofing contractor before selecting underlayment.