A Guide to Roofing Felt

Roofing felt is a crucial material in both residential and commercial construction, yet it often goes unnoticed. Acting as a protective layer, it helps shield roofs from water damage, extends their lifespan, and ensures a secure environment beneath. Here, we will explore what roofing felt is, its key purposes, and how it is installed.

What Is Roofing Felt?

Roofing felt, also known as underlayment or tar paper, is a water-resistant material that is laid between the roof deck and the external roofing material, such as shingles or tiles. Traditionally, it is made by saturating a fibrous base (typically made of organic materials or fibreglass) with asphalt or bitumen to improve its water resistance. It often comes in rolls and is widely used on pitched and flat roofs alike.

Modern advancements have brought synthetic roofing felts to the market, which are lighter, more durable, and offer enhanced water resistance compared to traditional felt.

What Does Roof Felt Do?

Roofing felt serves multiple vital purposes, including:

1. Waterproofing Roofing felt acts as an extra layer of defence against water infiltration. If shingles or tiles become damaged or dislodged, the felt helps prevent water from penetrating into the building structure.
2. Weather Protection During the roof installation process, roofing felt provides temporary protection from the elements, such as rain, snow, and wind, before the final roofing material is installed.
3. Improved Longevity Roofing felt protects the roof deck from moisture build-up, which can lead to wood rot and structural damage over time. It helps prolong the lifespan of the roof.
4. A Uniform Surface Roofing felt creates a smooth, even base for installing tiles, shingles, or other external roofing materials.
5. Prevention of Resin Stains If your roof deck is made from wood, roofing felt prevents natural wood resins from staining the final roofing material.

How Is Roofing Felt Installed?

The installation process for roofing felt varies depending on whether you are working on a flat or pitched roof, but generally the steps are as follows:

1. Prepare the Roof Deck Before installing roofing felt, ensure the roof deck is clean, dry, and free from debris. Any damaged sections should be repaired or replaced.
2. Lay the Roofing Felt Starting at the bottom of the roof (eaves), unroll the roofing felt horizontally across the deck. The felt should be laid flat and smooth to prevent wrinkles or air pockets.
3. Nail or Staple the Felt Use galvanised roofing nails or staples to secure the felt to the roof deck. Place fasteners approximately every 6 to 12 inches along the edges and in the centre of the roll for stability.
4. Overlap Each Row Overlapping is essential to prevent water infiltration. Typically, a 2-inch overlap is sufficient for pitched roofs, while flat roofs may require a larger overlap of around 4 inches.
5. Install Additional Layers Continue laying roofing felt in rows, working upward toward the roof ridge. Ensure each layer overlaps the one below it to maintain a watertight barrier.
6. Secure Final Edges Ensure all edges are properly nailed down, particularly around vents, chimneys, and other roof penetrations. Seal these areas with roof cement or flashing for added protection.

Once the roofing felt is installed, it serves as a temporary waterproof barrier until the final roofing material (tiles, shingles, or other coverings) is applied.

In summary, roofing felt plays a pivotal role in protecting roofs from water damage and ensuring their longevity. Whether you are constructing a new roof or making repairs, understanding its purpose and installation process is key to maintaining a durable, watertight structure.

If you are looking for roofing services in Exeter, please get in touch.

FAQs

What roofing felt should I use? 

The choice of roofing felt depends on the roof type and climate. Traditional bitumen-based felt is effective, but synthetic roofing felts offer superior durability, tear resistance, and water resistance.

How much overlap is needed for roofing felt on a flat roof? 

For flat roofs, an overlap of at least 4 inches is recommended to ensure proper water resistance.

How long can you leave roofing felt exposed? 

Roofing felt can typically remain exposed for up to 2 weeks in dry weather conditions. However, prolonged exposure to rain, sun, or wind can damage the felt, so covering it promptly is best.

Can rain get through the roofing felt? 

While roofing felt is water-resistant, it is not completely waterproof. If left exposed for long periods, heavy or consistent rainfall can saturate and compromise the material.