Roofing felt is a common underlayment used under shingles and other roof coverings. Knowing how long roofing felt can stay exposed is essential to prevent water intrusion, UV degradation, and installation delays. This article explains exposure limits, variables that affect felt lifespan, and practical steps to protect underlayment during construction or repair.
| Felt Type | Typical Safe Exposure | Primary Risk |
|---|---|---|
| Asphalt-Saturated Felt (15-lb) | 24–72 Hours | UV And Moisture Damage |
| Asphalt-Saturated Felt (30-lb) | 3–7 Days | Edge Drying, Tearing |
| Synthetic Underlayment | 30–180 Days | UV Over Long Term |
Why Exposure Time Matters
Roofing felt functions as a temporary water-shedding layer and secondary moisture barrier until the finished roof is installed. Prolonged exposure reduces its ability to shed water and resist wind uplift, leading to leaks and substrate damage. Contractors and homeowners must balance scheduling constraints with material limits to avoid costly rework.
Factors That Affect Roofing Felt Durability
Several environmental and product-related factors determine how long roofing felt can stay exposed. Sunlight, temperature, precipitation, wind, and foot traffic accelerate deterioration. Felt type, weight, and reinforcement also play critical roles. Understanding these variables helps set realistic exposure windows.
Sunlight And UV Exposure
UV radiation breaks down bitumen and organic fibers in traditional felts. Direct sun shortens safe exposure times dramatically, especially in high-sun regions. Synthetic underlayments resist UV better but are not immune to degradation.
Temperature Extremes
High heat can soften asphalt-saturated felt, making it tacky and prone to tracking and tearing. Cold temperatures make felt brittle and susceptible to cracking when walked on. Both extremes reduce effective exposure windows.
Moisture And Precipitation
Rain or snow can saturate felt, causing wrinkles, delamination, and loss of adherence to the roof deck. Once wet, felt may lose tensile strength, making it vulnerable during subsequent handling. Keeping felt dry is essential for maintaining its protective function.
Wind And Mechanical Damage
Wind can lift and tear exposed felt, especially at edges and penetrations. Foot traffic and tools cause punctures and abrasions that compromise the barrier. Secure fastening and edge protection mitigate mechanical risks.
Types Of Underlayment And Typical Exposure Limits
Different underlayments offer varying resistance to weather and UV, which directly affects exposure limits. Below are commonly used options and practical exposure guidance.
| Underlayment Type | Characteristics | Recommended Max Exposure |
|---|---|---|
| 15-lb Asphalt Felt | Traditional, economical, lower tensile strength | 24–72 hours in sun; up to a week in shade |
| 30-lb Asphalt Felt | Heavier, more tear-resistant | 3–7 days depending on conditions |
| Synthetic Underlayment | Polypropylene/polyester blends, high UV resistance | 30–180 days per manufacturer |
| Self-Adhered Membranes | Sticky, waterproof, often used in valleys | Variable—follow manufacturer, typically 30–90 days |
Manufacturer Guidelines And Building Codes
Manufacturers provide specific exposure ratings for their underlayments, and these should take precedence. Many building codes and local ordinances require following manufacturer instructions for installation and exposure limits as part of code-compliant construction. Always review technical data sheets before selecting materials.
Best Practices For Protecting Exposed Felt
Adopting proactive protection measures extends exposure time and reduces risk. Implementing simple tactics can prevent damage while awaiting roof covering installation.
- Plan Install Sequencing To Minimize Exposure: Coordinate shingle/metal deliveries to install soon after underlayment.
- Limit Work Delays Avoid leaving felt exposed over weekends or holidays in bad weather seasons.
- Secure Edges And Penetrations Use staples, cap nails, or tapes specified by the manufacturer to prevent wind lift.
- Cover With Tarp For Longer Delays Use breathable tarps and proper fastening to avoid trapping moisture while protecting from precipitation and UV.
- Use Synthetic Underlayment Where Practical For longer exposure windows and improved tear resistance.
How To Assess Felt After Exposure
When felt has been exposed, quick assessment helps decide whether replacement is needed. Inspect visual signs and perform simple checks to evaluate integrity.
- Look For UV Chalking Or Color Fading—Visible degradation indicates reduced waterproofing.
- Check For Rips, Tears And Punctures—Small repairs may suffice; widespread damage requires replacement.
- Feel For Brittleness Or Loss Of Flexibility—Stiffness often means the bitumen has oxidized.
- Inspect For Saturation Or Mold—Wet or stained felt has lost protective function and risks deck damage.
Repair And Replacement Options
Decisions depend on extent of damage and project timeline. Small localized damage can often be repaired; extensive deterioration typically requires full replacement of the affected underlayment.
- Patching Minor Tears Use approved roofing cement and compatible patches, sealing edges and butt joints per manufacturer guidance.
- Flashing And Sealants Replace or reseal flashings around penetrations to restore watertightness.
- Full Underlayment Replacement When felt is brittle, saturated, or UV-frayed, remove and install new underlayment to meet warranty and code.
Estimating Exposure Time For Specific Conditions
Practical exposure estimates help planning. Use conservative assumptions: in direct sun and winds, traditional 15-lb felt should be considered at risk after one day. In shaded, dry climates, 30-lb felt may last several days. Synthetic underlayments extend safe windows substantially, sometimes to months, but always verify manufacturer ratings.
Cost And Warranty Considerations
Replacing underlayment adds labor and material costs; indirect costs include delays to other trades. Many roofing material warranties require proper underlayment handling and installation. Improper exposure can void parts of a roofing warranty, so keep records of material specs and installation timelines.
Maintenance Tips During Extended Exposure
If extended exposure is unavoidable, follow these steps to protect felt and the roof deck until roofing is completed.
- Inspect Daily After Storms Check for uplift or water pooling.
- Use Temporary Fasteners Re-secure edges and overlaps after high winds.
- Avoid Walking Excessively Limit traffic to reduce punctures and tears.
- Schedule Final Covering Prioritize installation of shingles or metal panels as soon as feasible.
Regional Considerations For The U.S.
Climate impacts exposure guidelines. In the Sun Belt, UV and heat shorten life expectancy of asphalt felts. In the Pacific Northwest, frequent rain demands immediate waterproofing. In cold northern regions, freeze-thaw cycles can harm felt if left exposed. Adjust exposure allowances based on local climate patterns.
Common Misconceptions
Several myths lead to risky practice. One is that all felts perform the same—differences are substantial. Another is that tarping always protects; improper tarping can trap moisture and worsen damage. Rely on manufacturer instructions and evidence-based practices rather than anecdote.
Key Takeaways For Contractors And Homeowners
Roofing felt exposure must be managed proactively. Use thicker or synthetic underlayments when delays are possible, secure edges, follow manufacturer exposure limits, and inspect before final covering. When in doubt, replace compromised felt to avoid leaks and warranty issues.
Resources And Where To Learn More
Technical data sheets from manufacturers, building code sections for roofing underlayments, and industry trade organizations (e.g., NRCA) provide authoritative guidance. Refer to product-specific literature for exact exposure ratings and consult local code officials for compliance questions.