Installing tar paper, or roofing felt, on a wet roof is generally discouraged. Moisture can compromise the felt’s adhesion, reduce tear resistance, and trap water beneath the underlayment, leading to rot, mold, and future leaks. This article explains when it might be possible, the risks involved, and safer alternatives for weatherproofing a roof project in damp conditions.
Understanding Tar Paper And Its Purpose
Tar paper, also known as asphalt-saturated felt, is a traditional roofing underlayment that provides a moisture barrier between the roof deck and shingles or other roofing materials. It helps shed water and offers slip resistance for roofing crews. Modern synthetic underlayments have largely replaced felt in many installations due to better resistance to tearing and moisture. When installed correctly, tar paper contributes to the roof assembly’s long-term durability, but it relies on dry conditions for proper adhesion and performance.
Assessing The Weather And The Roof Surface
Before attempting any underlayment installation, evaluate the roof surface and weather. Ideal conditions are dry, moderate temperatures, and a clean, dry deck. On a wet roof, the surface can be slick, and moisture can prevent adhesive from bonding and cause the felt to lift or wrinkle. Frost, dew, or rain droplets on the deck further increase the risk of trapped moisture beneath the underlayment. If the roof remains wet, postponing installation is the safer choice.
Can You Install Tar Paper On A Wet Roof?
In most cases, installing tar paper on a wet roof is not recommended. The key risks include poor adhesion, rapid deterioration of the underlayment’s bond, and the potential for moisture to become trapped beneath the felt. Trapped moisture can accelerate deck rot and reduce the effectiveness of the barrier. Exceptions exist when temporary protective measures are used and the roof deck is prepared quickly, but these circumstances are rare and require professional judgment.
Safer Alternatives When Conditions Are Damp
When wind and weather make dry installation impractical, consider these alternatives to protect the roof deck and maintain progress:
- Self-Adhering Or Rubberized Underlayment: Some products are designed to adhere to a damp but clean deck. Carefully follow manufacturer guidelines and test a small area first.
- Roofing Membrane Drops: Peel-and-stick continuous membranes can provide moisture protection while work is paused. They should be compatible with the chosen final roofing material.
- Temporary Weather Protection: Use tarps or temporary roofing fabric to keep the deck dry until conditions improve, then resume underlayment installation.
- Delay And Recheck: If possible, delay work until the deck dries and weather forecasts predict a window of dry conditions.
Steps If Installation Is Absolutely Necessary In Damp Conditions
If a professional determines that proceeding is acceptable, follow these careful steps to minimize risk. Note that these steps are conditional and depend on product specifications and local codes:
- Consult Product Data: Read the manufacturer’s installation guidelines for damp or marginally dry substrates; some products tolerate limited moisture.
- Deck Preparation: Remove standing water, sweep debris, and wipe the surface with a dry, absorbent cloth. The deck must be as dry as possible.
- Drying Aids: Use portable heaters or warm air to reduce surface moisture. Avoid open flames, and maintain safe distances from flammable materials.
- Adhesive Checks: If using self-adhering membranes, ensure the adhesive can bond to lightly damp surfaces as per the label.
- Flashing And Edges: Pay extra attention to edges and flashing, where moisture can penetrate. Install these components carefully to prevent leaks.
- Thorough Inspection: After installation, perform a close inspection for wrinkles, bubbles, or lifted edges and address immediately.
Important: This approach carries higher risk. If any sign of ongoing moisture remains, stop work and postpone until the deck dries and weather improves.
Installation Best Practices For Dry Or Fully Dry Decks
When conditions are dry, follow these best practices to maximize the effectiveness of tar paper underlayment:
- Use The Right Underlayment: Choose high-quality asphalt-saturated felt or a modern synthetic underlayment compatible with the roofing material.
- Proper Nailing Pattern: Apply nails or staples as specified, keeping fasteners perpendicular and evenly spaced to prevent lift.
- Overlap And Direction: Place sheets with proper overlap (typically 2 to 4 inches, depending on product) and work from bottom to top to shed water.
- Seam Reinforcement: Use tape or manufacturer-recommended fasteners for seams when required by product guidelines.
- Ventilation And Safety: Ensure adequate ventilation in attic spaces and follow fall protection guidelines during installation.
Maintenance After Installation
Post-installation maintenance helps preserve the underlayment’s effectiveness. Inspect after heavy rain or wind events for lifted edges, wrinkles, or water infiltration. Clean debris and re-secure any loose areas promptly. If moisture damage is detected in the roof deck or underlayment, address it immediately to prevent further deterioration and potential leaks.
Understanding Local Codes And Roofing Warranties
Local building codes and warranty terms can influence whether underlayment can be installed on damp surfaces. Some codes require dry substrates for underlayment installation, while certain products come with warranties contingent on installation conditions. Always verify code requirements and product warranties before proceeding in damp conditions.
FAQ And Quick Tips
- Q: Is tar paper necessary under modern shingles? A: Many modern roofs use synthetic underlayment or roof membranes, but tar paper is still common in many installations for added moisture protection.
- Q: Can you walk on a wet roof? A: Walking on a wet roof increases the risk of slips and damages. Use proper footwear and safety equipment, and minimize traffic when possible.
- Q: How long should tar paper last? A: With proper installation and dry conditions, underlayment can last 15–40 years depending on climate and material. Wet conditions reduce lifespan.