Using Roofing Felt on Walls: Practicality and Considerations
Roofing felt is widely recognized for its role in protecting roofs from moisture and weather damage. But can roofing felt be used on walls? This question is common among homeowners and builders seeking cost-effective or efficient moisture barriers for wall construction or renovation. While roofing felt is designed primarily for roofs, it can also be applied on walls under specific circumstances, provided its properties and limitations are understood.
| Aspect | Roofing Felt on Walls | Typical Wall Barriers |
|---|---|---|
| Primary Function | Waterproofing, moisture barrier for roofing | Vapor barrier, insulation support, moisture barrier |
| Material | Asphalt-saturated paper or synthetic material | Foil-faced, polyethylene sheets, house wraps (e.g., Tyvek) |
| Durability | Good under roofing; less UV resistant outdoors on walls | Designed for exposure during construction, UV-resistant options |
| Breathability | Generally low permeability | Varies; some allow vapor permeability to prevent moisture buildup |
| Common Uses | Under shingles, roof decks | Behind siding, between sheathing and exterior cladding |
What Is Roofing Felt and Its Main Characteristics?
Roofing felt is a type of protective underlayment made from saturated paper or fabric with asphalt or bitumen coating. It creates a waterproof barrier beneath roofing materials to prevent moisture penetration. Roofing felt comes in various thicknesses—typically 15-pound or 30-pound grades—and is valued for its simplicity, affordability, and water resistance.
While traditional felt is made from organic materials, modern synthetic roofing felts improve on durability and tear resistance. However, roofing felt is mainly manufactured for horizontal applications like roofs where UV exposure is limited once shingles are installed.
Using Roofing Felt on Walls: When and Why Is It Done?
Roofing felt can be used on walls primarily as a temporary weather barrier during construction phases or in cases where cost constraints or material availability dictate its use. It offers a degree of moisture protection by shedding water, reducing infiltration, and protecting underlying sheathing.
Examples of wall uses include:
- Temporary weather barrier to protect framed walls during construction
- Cost-effective moisture barrier in shed or outbuilding construction where high-grade house wrap may not be critical
- Under certain siding types where a simple water-resistant barrier is sufficient
Despite these uses, roofing felt is not an ideal long-term solution for walls. It tends to degrade under prolonged UV exposure and does not provide the breathability necessary for healthy wall assemblies.
Differences Between Roofing Felt and Proper Wall Barriers
Moisture management in walls requires materials that balance water resistance with vapor permeability to prevent trapped moisture, which can cause mold and structural damage.
| Feature | Roofing Felt | Wall Moisture Barriers |
|---|---|---|
| UV Resistance | Limited – degrades with sun exposure | Often UV stabilized for outdoor exposure |
| Vapor Permeability | Low – inhibits drying of wall sheathing | High or variable – allows walls to breathe |
| Water Resistance | Excellent water barrier | Good water resistance while allowing vapor to pass |
| Durability | Designed for roof slopes, limited wall durability | Engineered for vertical exposure and long-term use |
Potential Issues Using Roofing Felt on Exterior Walls
Prolonged UV exposure causes roofing felt to crack, become brittle, and eventually degrade when used on walls. Since walls are vertical and often exposed for long periods, this limits felt’s lifespan.
Moreover, roofing felt’s low vapor permeability traps moisture inside wall cavities, risking mold growth and wood rot. Proper house wraps or breathable barriers mitigate this risk by allowing moisture to escape while preventing water infiltration.
Adhesion and fastening methods designed for roofing may not be optimal for vertical walls, potentially resulting in peeling or gaps.
Best Practices for Moisture Barriers on Walls
For exterior walls, selecting the correct weather-resistant barrier is vital for long-term durability and indoor air quality:
- House Wraps: Materials like Tyvek provide water resistance and breathability, facilitating vapor diffusion.
- Building Paper: Asphalt-saturated felt paper is often used on walls but typically specific grades designed for wall moisture control, like 15-pound felt, which allows limited permeability.
- Fluid-Applied Barriers: Liquid membranes that are seamless and durable, often used in commercial and high-end residential construction.
- Vapor Barriers: Used within wall cavities to regulate moisture migration, but placement depends on climate zones.
Consulting local building codes and following manufacturer recommendations ensure materials meet regional climate challenges and performance standards.
When Roofing Felt Is Suitable for Walls
Despite limitations, roofing felt can be considered in scenarios such as:
- Temporary Protection: Shielding building frames during construction before installing permanent cladding.
- Low-Exposure Structures: Interior walls or protected exterior surfaces where direct sunlight and weather contact are minimal.
- Non-Residential Uses: Barns, sheds, or outbuildings where longevity and breathability are less critical.
In these cases, roofing felt offers a simple, economical solution but should not replace specialized wall barrier systems for finished exteriors.
Installation Tips When Using Felt on Walls
Proper installation improves functionality and longevity even when using roofing felt:
- Use the appropriate felt grade—15-pound felt is better suited for walls than 30-pound.
- Overlap seams by at least 6 inches and secure tightly to avoid gaps.
- Install with the coated side facing outward to improve water shedding.
- Cover felt quickly with siding or cladding to reduce UV exposure.
- Ensure walls have proper ventilation to help moisture escape and prevent condensation.
Summary
Using roofing felt on walls is possible but limited by the material’s design and durability challenges. While it provides temporary moisture protection and may serve in less demanding applications, it is not the best choice for long-term exterior wall barriers. Proper materials like house wraps, vapor-permeable membranes, and building papers designed specifically for walls deliver better performance for moisture control and durability.