Roofing felt, also known as tar paper, is an asphalt-saturated felt used as an underlayment for shingles and other roofing materials. When installing a roof, roofing felt is applied over the roof decking but under the final exterior roof covering. This provides an extra water-resistant barrier between the interior structure and exterior elements.
While roofing felt is designed to be covered up by shingles or other materials, it is sometimes temporarily left exposed during roof construction or repair. So how long can roofing felt safely stay uncovered before issues arise?
The Purpose of Roofing Felt
Roofing felt serves several important functions as an underlayment:
- Prevents Leaks: The layers of asphalt coating make roofing felt waterproof to block water from penetrating the roof deck. This provides a secondary barrier against leaks, protecting the roof structure and interior.
- Reduces Friction: The smooth felt surface allows the exterior roofing materials, like shingles, to expand and contract more easily with temperature changes. Less friction means fewer cracks or tears in the exterior roof.
- Adds Stability: Roofing felt creates a more uniform surface over inconsistencies in the roof deck, like knots in wood or seams between panels. This provides a stable base for the roof covering.
- Resists Wind Damage: The reinforced felt withstands force from high winds better than roof decking alone. It provides extra hold against wind uplift.
- Aids in Insulation: The layers of asphalt paper provide a small amount of extra insulation for the roof structure. This can reduce heat transfer and energy costs.
How Long Can It Stay Exposed?
Roofing felt is intended to be covered up soon after installation. Most roofing felt products are not designed for long-term exposure to the elements. Here are general guidelines on exposure limits:
- 1-2 Weeks: Most standard roofing felts can handle brief exposure with minimal risk of issues. But leaving it uncovered for over 2 weeks is not recommended.
- 90 Days Max: Some premium or specialized roofing felts may be warrantied for up to 90 days of exposure. But past 90 days, the condition will deteriorate.
- Not Indefinitely: No roofing felt products are designed to permanently function as a finished roof surface. Leaving roofing felt uncovered indefinitely will lead to failure.
Exceeding these exposure limits can lead to problems like:
- Brittleness and cracking from sun damage
- Loss of water resistance as coatings wear away
- Wind uplift under the felt causing rips
- Leaks and interior water damage
So while roofing felt can handle a short uncovered period, it should always be treated as a temporary underlayment until permanent roofing goes on top.
Factors That Shorten Safe Exposure Time
Several factors can accelerate the deterioration of exposed roofing felt and shorten the safe exposure period:
- Hot Climate: In hot regions, sun and heat damage the roofing felt more quickly. The asphalt coatings soften and materials dry out faster.
- Lots of Sun: South- or west-facing roofs and roofs at high elevations receive more intense sunlight. This can degrade exposed felt quicker.
- Wind and Rain: Wet, windy conditions combined put more stress on the felt and wash away protective coatings.
- Poor Installation: Wrinkles, gaps, or inadequate fastening reduce the felt’s ability to withstand exposure. Proper installation is key.
- Low-Quality Felt: Cheaper roofing felts often have fewer asphalt coatings and weaker reinforcement. They break down faster when uncovered.
- Steep Slope Roofs: Steeply angled roofs can allow the felt to slide or lift off before exterior roofing is installed.
Protecting Exposed Roofing Felt
If roofing felt needs to stay uncovered longer than recommended, there are temporary measures that can protect it:
- Cover the felt with waterproof tarps or plastic sheeting between work sessions.
- Weight down loose edges or seams with boards, bricks, or gravel bags to prevent wind uplift.
- Use a high-quality felt with the maximum exposure rating for your climate.
- Apply an acrylic coating or additional asphalt layer to re-waterproof the surface.
- Limit foot traffic and avoid dragging tools over uncovered felt to prevent tears.
- Check for and repair any loose nails, wrinkles, or gaps in the felt that could allow water intrusion.
Consult the Manufacturer’s Recommendations
For the most accurate exposure guidelines, check the manufacturer’s specifications for your particular roofing felt product. Different materials and coatings can provide better or worse temporary exposure resistance. Follow their recommended time limits closely.
In general, roofing felt should not remain uncovered for more than a few weeks at the very most. Exceeding exposure limits risks moisture damage, leaks, and even total failure of the felt. Protect or cover exposed felt as soon as possible to avoid compromising the roof. With reasonable care, roofing felt can serve its purpose as a reliable underlayment.