What is Roofing Felt? Can It Get Wet?

What is Roofing Felt

What is roofing felt? Roofing felt, also known as felt underlayment, is a thin water-shedding barrier that is installed between roof shingles and the decking to protect the roof from moisture infiltration, wind-driven rain, and snow.

Can roofing felt get wet? The answer is Yes, roofing felt can get wet but it is designed to repel water rather than absorb it.

Key Takeaways:

  • Roofing felt is an asphalt-saturated organic or fiberglass mat moisture barrier.
  • It is installed under shingles and other roofing materials to prevent leaks.
  • Roofing felt should not get excessively wet, as moisture can compromise its waterproofing abilities.
  • Allow roofing felt to fully dry out before continuing roof work after exposure to moisture.
  • Use caution when walking on wet felt to avoid damage.

What is Roofing Felt?

Roofing felt, also called tar paper, is a material applied in sheets underneath roofing materials like shingles and tiles. It is made by saturating a reinforced paper or fiberglass mat with asphalt.

The key functions of roofing felt are:

  • Moisture barrier – The asphalt coating repels liquid water to prevent leaks.
  • Protection – Felt buffers the roof deck from damage by overlaying materials.
  • Adhesion – The surface provides grip for shingles and other roofing.

Roofing felt weighs around 18-30 pounds per 100 square feet. It commonly comes in rolls 3 feet wide and 36-144 feet long.

There are two main categories of roofing felt:

  • Organic – The traditional type uses paper reinforced with wood fibers.
  • Fiberglass – A stronger synthetic option with a fiberglass mat.
Roofing Felt TypeProsCons
Organic– More pliable- Better conforms to surfaces– Absorbs more moisture- Prone to tearing
Fiberglass– Stronger and tear-resistant- Maintains strength when wet– Less flexible- Difficult to cut

Within these two categories, there are different types numbered from lightest (#15) to heaviest (#30). The higher the number, the thicker the felt and the more layers it contains.

Heavier felt types are ideal for steep-sloped roofs, while lighter felt suits low-sloped or flat roofs. Regional building codes also recommend minimum felt weights for various roof types.

How is Roofing Felt Used?

Roofing felt is a secondary layer installed over the roof deck and underneath other exterior roof coverings. It serves as an added moisture barrier between the inside of the building and the outside elements.

Here are the key steps for installing roofing felt:

  1. Start by fastening the roof decking material, such as plywood or OSB. Make sure the surface is clean.
  2. Roll out the felt parallel to the roof eaves. Use galvanized roofing nails to tack it in place temporarily.
  3. Overlap horizontal seams by 2-4 inches and vertical end seams by 4-6 inches. This provides double coverage.
  4. At valleys and around dormers, do triple coverage with felt overlaps.
  5. Apply final roofing materials like shingles on top of the felt. The shingle fasteners will hold the felt permanently in place.
  6. Trim any excess felt hanging over roof edges once done.

Proper installation is key for roofing felt to work effectively. Following manufacturer specifications for the specific type used is also important.

Can Roofing Felt Get Wet

Can Roofing Felt Get Wet?

Now that we’ve covered the roofing felt basics, let’s address the critical question – can roofing felt get wet?

The short answer is – yes, roofing felt is made to withstand some moisture. But there are limits to how wet it should get.

During installation, it’s normal for roofing felt to be exposed to some rain and dew before shingles go on. But it shouldn’t get soaked through or sit under collected water.

When roofing felt gets overly wet for extended periods, problems can occur:

  • Loss of asphalt – Excessive moisture washes away the waterproofing asphalt coating.
  • Loss of strength – Wet paper or fiberglass mats become weaker and prone to tearing.
  • Buckling – Saturated felt can wrinkle up under other roofing materials.
  • Mold growth – Moisture enables mold colonies to start growing on the surface.
  • Difficulty drying out – Felt applied over a wet roof deck takes longer to dry.

To minimize issues, builders should:

  • Not install felt when heavy rain is imminent.
  • Work quickly to cover with shingles once felt is down.
  • Exercise caution when walking on felt in damp conditions.
  • Allow extra time for drying if the felt gets very wet before proceeding.
  • Replace any felt that wrinkles or molds over from excess moisture.

With reasonable care during construction, roofing felt can handle small amounts of moisture from weather and condensation. 

But prolonged wetness compromises its performance and longevity.

Working on Roofs with Wet Felt

Sometimes, roofing projects get rained out, and it’s not possible to avoid the felt getting soaked. What do you do in this situation?

If work must continue over damp felt, extra precautions are necessary:

  • Let the roof dry out entirely before adding shingles, which seal in moisture.
  • Replace any areas where felt has torn, wrinkled, or pulled away.
  • Add an extra layer of felt over damaged sections for fortification.
  • Walk carefully on wet felt to avoid ripping it with foot traffic.
  • Use plastic tarps to keep overnight dew or light rain from further wetting the roof.
  • Allow a few days of dry weather to fully dry the roof before finishing.

Rushing through roofing over wet felt leads to problems down the road. It’s better to wait for proper drying conditions first.

Signs of Excess Moisture in Roofing Felt

Even after installation, excessive moisture can compromise roofing felt over time. Signs this may be occurring include:

  • Dark staining – Wet areas show up darker than the surrounding felt.
  • Blistering – Bubbles form under the felt from trapped moisture.
  • Wrinkling – Felt buckles up off the roof deck as it expands when wet.
  • Mold/mildew – Discolored blotchy patches from mold colonies forming.
  • Leaks – Water drips through nail holes or damaged sections of saturated felt.

Don’t ignore these warning signs of waterlogged felt. Address the source of moisture quickly before rot and leaks occur.

If small sections are affected, spot repairs may suffice:

  • Dry out the roof section thoroughly.
  • Cutaway stained/damaged felt.
  • Replace with a fresh felt patch.
  • Seal edges with roofing cement.

For widespread moisture issues, a complete roof replacement may be needed. Finding and fixing the leak source is also critical.

Maintaining Roofing Felt

Like other roofing components, roofing felt requires periodic maintenance to maximize lifespan.

  • Have the roof professionally inspected every 2-3 years. They can spot felt issues early.
  • Trim back overhanging trees to limit dampness from shade.
  • Clean gutters and downspouts regularly to prevent water buildup.
  • Replace any missing or loose shingles right away that expose the felt.
  • Watch for holes, tears, and gaps around flashing that need resealing.
  • Combat mold growth by spraying bleach solution on discolored patches.

With proper installation and care, roofing felt typically lasts as long as the shingles before needing replacement. Catching moisture problems quickly prevents costly damage.

Roofing Felt and Moisture

Roofing felt provides a water-resistant barrier between your roof deck and shingles against the elements. But it has its limits for how much wetness exposure it can handle.

Keep these guidelines in mind:

  • Install roofing felt only when suitable dry weather is expected.
  • Work efficiently to cover it with shingles as soon as possible.
  • Use caution when walking over damp felt to avoid ripping it.
  • Allow adequate drying time if felt does get excessively wet before finishing the roof.
  • Repair or replace affected areas if you see dark staining, blistering, buckling, or mold growth.
  • Perform regular roof maintenance to preserve the felt condition.

With proper care taken during installation and over time, roofing felt does an excellent job protecting against leaks. But moisture control is key to maximizing its performance and longevity.

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