The efficacy of tar paper moisture barrier is a frequently debated topic within the building industry. The International Residential Code (IRC) defines requirements for moisture management, a crucial attribute when considering the role of tar paper moisture barrier. Proper installation, often achieved using tools like a roofing nailer, significantly impacts the performance of the tar paper moisture barrier. Concerns about long-term durability often prompt comparisons with synthetic alternatives, highlighting the ongoing evolution of building envelope strategies related to a tar paper moisture barrier.
Image taken from the YouTube channel Ask the Builder , from the video titled Tar Paper Facts .
Understanding the Effectiveness of Tar Paper Moisture Barriers
This article will explore the function, application, and efficacy of tar paper as a moisture barrier in residential construction. We’ll analyze how it’s meant to work, potential weaknesses, and explore its role in the broader context of moisture management. The goal is to provide a clear and objective understanding of the question: "Does a tar paper moisture barrier really work?".
What is a Tar Paper Moisture Barrier?
Definition and Composition
Tar paper, also sometimes called roofing felt, is a heavy paper saturated with tar or asphalt. Its primary purpose in wall construction is to act as a water-resistive barrier (WRB). It’s installed between the sheathing (typically plywood or OSB) and the exterior cladding (e.g., siding, brick veneer).
Historical Context
Tar paper was one of the earliest materials used for moisture protection in buildings. Its popularity stems from its affordability and relative ease of installation.
Common Types of Tar Paper
Tar paper is usually classified by weight per 100 square feet, which influences its thickness and water resistance:
- 15-lb Felt: A lighter and more common type.
- 30-lb Felt: Heavier and offers potentially better water resistance.
How a Tar Paper Moisture Barrier is Supposed to Work
Primary Function: Water Resistance
The main idea behind using tar paper is to prevent bulk water (rain, snowmelt) from penetrating the exterior cladding and reaching the wall sheathing. It acts as a shield, diverting water away from the structural elements of the wall.
Secondary Function: Air Barrier (Limited)
While tar paper is not specifically designed as an air barrier, it does offer some resistance to air movement. However, its effectiveness in this role is limited due to its permeability and the potential for gaps at seams and around penetrations.
Breathability Considerations
A crucial aspect of any WRB is its ability to allow moisture vapor to escape from the wall cavity. This "breathability" helps to prevent condensation and mold growth within the wall. Tar paper is considered less breathable than some newer synthetic WRBs.
Potential Weaknesses and Limitations of Tar Paper
Vulnerability to UV Degradation
Prolonged exposure to sunlight (ultraviolet radiation) can cause tar paper to deteriorate over time. This can lead to cracking, embrittlement, and reduced water resistance. It needs to be covered by exterior cladding in a timely manner.
Tear Resistance and Durability
Compared to some synthetic WRBs, tar paper can be more susceptible to tearing during installation, especially in windy conditions. This can compromise its effectiveness as a water barrier.
Seam and Overlap Issues
Proper overlapping of tar paper sheets is essential to prevent water penetration. Incorrect installation can create pathways for water to enter the wall assembly. Specific overlap requirements are often mandated by local building codes.
Limited Breathability
The relatively low permeability of tar paper can trap moisture within the wall cavity, especially in humid climates or poorly ventilated buildings. This can lead to moisture accumulation and potential problems with mold and rot.
Installation Best Practices for Tar Paper Moisture Barriers
Proper Overlap
Adhere to the manufacturer’s recommendations and local building codes regarding the correct amount of overlap between tar paper sheets. Typically, a minimum overlap of 2 inches is required horizontally and 6 inches vertically.
Secure Fastening
Use roofing nails or staples to securely fasten the tar paper to the sheathing. Ensure that fasteners are spaced appropriately to prevent tearing or billowing.
Sealing Penetrations
Carefully seal around all penetrations in the wall, such as windows, doors, and pipes. Use appropriate flashing materials and sealants to create a watertight barrier.
Addressing Tears and Damage
Repair any tears or damage to the tar paper immediately. Use patches of tar paper and roofing cement to seal the affected areas.
Alternative Moisture Barrier Options
The market offers a range of alternative WRBs, each with its own advantages and disadvantages:
- Synthetic WRBs (e.g., Tyvek, WeatherShield): These are typically more durable, breathable, and UV resistant than tar paper.
- Liquid-Applied Membranes: These create a seamless, waterproof barrier and can be especially useful in complex wall designs.
- Self-Adhering Membranes: These offer excellent adhesion and water resistance and are often used around windows and doors.
The choice of WRB should be based on factors such as climate, building design, budget, and local building codes.
Comparative Table: Tar Paper vs. Synthetic WRBs
| Feature | Tar Paper | Synthetic WRBs |
|---|---|---|
| Water Resistance | Good (when properly installed) | Excellent |
| Breathability | Lower | Higher |
| Durability | Lower | Higher |
| UV Resistance | Lower | Higher |
| Cost | Lower | Higher |
| Ease of Installation | Moderate | Moderate to Easy |
So, what’s the verdict? Hopefully, you now have a better understanding of whether a tar paper moisture barrier is right for your project. Happy building!