The question of using roofing felt on walls touches on weather resistance, cost, and building code compliance. Roofing felt, also known as tar paper or underlayment, is designed to protect roof decks from moisture. On walls, its performance, installation requirements, and long-term durability differ. This article outlines what roofing felt is, whether it can be used on walls, practical applications, installation tips, limitations, and viable alternatives for wall weatherproofing and vapor management.
What Is Roofing Felt
Roofing felt is a flexible sheet material made from asphalt-saturated textile or fibrous material. It acts as a secondary moisture barrier beneath shingles or siding. Felt generally comes in weights such as 15, 30, or higher, with the heavier varieties offering more tear resistance. On roofs, it provides temporary protection during construction and an extra layer against wind-driven rain. When used on walls, its performance depends on substrate, climate, and compatibility with the exterior finish.
Can It Be Used On Walls
In general, roofing felt is not intended as a primary wall weather barrier in most U.S. building envelopes. Some builders may use felt behind siding or as a temporary water barrier during installation, but it should not replace a purpose-built wall assembly. Factors that limit its use on walls include UV resistance, long-term durability, breathability concerns, and code requirements for exterior barriers. For walls, building codes typically specify a weather-resistive barrier (WRB) or house wrap designed to shed water while allowing vapor to escape. Using felt alone on walls risks water intrusion, peeling, and accelerated deterioration under sun exposure.
That said, there are niche scenarios where felt or felt-like materials might appear in wall assemblies, usually as part of a larger WRB system or in temporary framing situations. When considering such a use, it is essential to verify local codes, consult a structural or building envelope professional, and ensure compatibility with the chosen exterior cladding.
Best Uses And Limitations
Key considerations for using roofing felt in wall assemblies include:
- Moisture management: Walls require barriers that shed bulk water and permit vapor diffusion. Felt alone does not reliably manage bulk water or moisture migration in most climates.
- Durability: Sun exposure degrades asphalt-based felt, reducing its effectiveness over time when used on vertical surfaces.
- Air and water infiltration: A properly installed WRB with flashing and penetrations is designed to handle wind-driven rain and leaks better than felt.
- Code compliance: Many building codes restrict or do not recognize roofing felt as an exterior weather barrier for walls.
In summary, while roofing felt can appear in wall assemblies in limited, non-primary roles, it is not generally recommended as a substitute for a dedicated WRB behind siding or stucco.
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Installation Considerations
If a project involves using roofing felt on or around walls in a temporary or transitional role, adherence to best practices is crucial:
- Substrate preparation: Ensure a clean, dry surface and sound sheathing. Moisture damage should be repaired prior to any barrier installation.
- Sealing and overlaps: Overlap felt sheets in the direction of water flow. Use compatible fasteners and sealant to minimize edge lifting.
- Flashing: Proper flashing around windows, doors, and penetrations is essential. Felt should not replace flashing details; flashing must be integrated with the exterior cladding system.
- Ventilation and drainage: Maintain proper ventilation behind the wall to prevent moisture buildup. Drainage planes must be preserved to direct water away from the structure.
- Inspection and maintenance: Regular checks for deterioration, tearing, or water staining are necessary to catch failures early.
Consult local building codes or a licensed contractor before installing roofing felt on walls to ensure rules are followed and to prevent unintended damage.
Moisture, Insulation And Building Codes
The wall assembly demands a balance of vapor control, drainage, and insulation. Roofing felt contributes little to insulation and is not optimized for vapor diffusion on walls compared with modern WRBs. Codes such as the International Residential Code (IRC) and various state amendments require an approved WRB behind cladding, with ratings like Type 1 or Type 2 air barrier/water-resistive barrier systems. In coastal or high-humidity areas, vapor management becomes even more critical to prevent mold and timber decay. In most cases, using a purpose-built WRB with continuous flashing and properly installed siding delivers superior performance and code compliance compared with felt on walls.
When evaluating alternatives, homeowners should consider products like house wraps (with proper air barrier properties), drainage planes behind siding, and cladding systems designed for the climate. Ensuring that the chosen assembly meets the local code requirements reduces risk and improves long-term durability.
Alternative Wall Materials
Several effective options deliver reliable weather protection and moisture control for walls:
- House wraps: Breathable, water-resistant barriers that shed liquid water while allowing vapor to escape, often paired with flashing and sealing tapes.
- Liquid-applied barriers: Flexible coatings applied to the substrate to form a continuous moisture barrier, used in conjunction with exterior finishes.
- Rigid foam board with WRB: Insulated sheathing combined with a WRB improves energy efficiency and moisture management.
- Ventilated rainscreen systems: An exterior cladding with a ventilation gap backed by a WRB, providing excellent drainage and drying potential.
- Traditional siding with integrated barriers: Some siding products include built-in moisture barriers or are designed to pair with specific WRBs for optimal performance.
Choosing the right system depends on climate, exposure, desired insulation value, and maintenance expectations. A building professional can help tailor the assembly to local conditions and codes.
Maintenance And Longevity
Materials installed on walls should endure sun exposure, freeze-thaw cycles, and wind-driven rain. Roofing felt tends to deteriorate faster on vertical surfaces due to solar exposure and less protective layering than roof systems. For wall applications, expect faster aging signs such as cracking, tearing, or edge lifting if used improperly or without proper supporting layers. Regular exterior inspections after severe weather can prevent minor issues from becoming costly repairs. When in doubt, replacing felt with an approved WRB and compatible cladding is a prudent long-term approach.
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Bottom line: Roofing felt is not recommended as a primary wall weather barrier in most U.S. homes. Its use on walls is limited, and code-compliant WRBs provide more reliable moisture management, durability, and long-term performance. For durable, code-compliant walls, rely on a dedicated WRB system paired with appropriate flashing and exterior cladding, and reserve roofing felt for roofs or temporary construction needs where permitted.