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What is Felt Roofing? What is the Installation Process?

Table of Contents

Felt Roofing
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A felt roof refers to a type of roofing material made from layers of bitumen (a sticky, black, and viscous material) and felt (a fabric made from fibres such as wool or polyester). It is commonly used for flat or low-sloped roofs in residential and commercial buildings.

The process of installing a felt roof typically involves the following steps:

  1. Preparation
  2. Underlay Installation
  3. Torch-On or Pour-and-Roll Application
  4. Overlapping and Sealing
  5. Finishing

Preparation of Roof

Before installing a felt roof, proper preparation of the roof is crucial to ensure a smooth and effective installation. Here are the steps involved in preparing a roof for felt roof installation:

  1. Clear the Roof: Remove any existing roofing materials, such as old shingles or tiles, and clear the roof surface of debris, dirt, and loose materials. This can be done by sweeping, washing, or using a leaf blower.
  2. Inspect and Repair the Roof Deck: Thoroughly inspect the roof deck for any signs of structural issues, damage, or rot. Replace any damaged or rotted sections of the deck and repair any weak or sagging areas to ensure a solid foundation for the felt roof.
  3. Check for Proper Ventilation: Adequate ventilation is essential for a healthy roof system. Ensure that there are proper vents and openings to promote air circulation and prevent moisture buildup. If needed, install additional vents or make repairs to existing ones.
  4. Address Roof Flashings: Inspect and repair roof flashings, such as those around chimneys, vents, or skylights to ensure that they are properly sealed and in good condition to prevent water leakage.
  5. Check for Slope and Drainage: A proper slope and adequate drainage are essential to prevent water pooling on the roof. Check that the roof has a sufficient slope and that gutters and downspouts are in good working condition. Clear any clogged gutters or downspouts.
  6. Install Roofing Underlay: It is common to install a layer of roofing underlay or base sheet before applying the felt. This provides an additional layer of waterproofing and protection. Using nails or adhesive, the underlay should be securely fastened to the roof deck.
  7. Flashing and Edge Preparation: Install flashing around the roof edges, eaves, and other vulnerable areas to provide additional waterproofing. Ensure that all edges are properly sealed and that there is no potential for water penetration.
  8. Clean and Dry the Roof Surface: Ensure the roof surface is clean and dry before installing the felt. Remove any remaining debris or moisture to ensure optimal adhesion of the felt material.

Underlay Installation

Installing an underlay is essential in preparing the roof to install a felt roof, and the underlay provides an additional layer of waterproofing and protection. Here are the general steps involved in underlay installation for a felt roof:

  1. Choose the Underlay Material: Select an appropriate underlay material for your felt roof installation. Standard options include bitumen-impregnated roofing felt or synthetic underlayment. Ensure that the underlay material meets the required standards for waterproofing and durability.
  2. Measure and Cut the Underlay: Measure the roof area to determine the amount of underlay material needed. Roll out the underlay onto the roof and cut it to the appropriate size, leaving a few inches of overhang on all edges to ensure complete coverage.
  3. Secure the Underlay: Start at one corner or edge of the roof and unroll the underlay, positioning it parallel to the roof edge. Secure the underlay to the roof deck using roofing nails or staples. Place fasteners approximately every 6 to 12 inches along the edges and every 12 to 18 inches in the field.
  4. Overlap the Underlay: When installing multiple rolls of underlay, overlap the edges by a few inches to ensure proper waterproofing. The specific overlap distance will depend on the manufacturer’s instructions but typically ranges from 2 to 6 inches. Secure the overlaps using adhesive or additional fasteners as recommended.
  5. Install Underlay on Roof Protrusions: Cut the underlay around roof protrusions, such as chimneys, vents, or skylights. Extend the underlay up and around the protrusions, ensuring they are fully covered and sealed.
  6. Apply Underlay to Valleys: Extend the underlay into the valley in roof valleys or areas where two roof sections meet. Overlap the underlay from both roof sections to create a watertight seal.
  7. Secure and Seal Edges: Ensure that the edges of the underlay are securely fastened and sealed to prevent water infiltration. Use roofing nails, staples, or adhesive as the underlay manufacturer recommends.
  8. Inspect and Repair: Once the underlay is installed, inspect it for any tears, gaps, or lose sections. Repair any damaged areas or gaps by patching or replacing the underlay.
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Torch-On or Pour-and-Roll Application

Torch-On or Pour-and-Roll Application

When installing a felt roof, there are two standard methods for applying the layers of bitumen-impregnated felt: torch-on application and pour-and-roll application. Here’s a brief explanation of each method:

1. Torch-On Application:

  • In the torch-on application method, the layers of bitumen-impregnated felt adhere to the roof surface using a heating torch.
  • The process involves heating the underside of the felt material with a propane torch, which melts the bitumen and allows it to bond with the roof surface.
  • The heated felt is carefully rolled onto the roof, ensuring proper alignment and coverage.
  • As the felt is rolled out, pressure is applied to ensure good adhesion to the roof surface and to eliminate air pockets or bubbles.
  • The process is repeated for each layer of felt, ensuring that overlaps are adequately sealed, and the entire roof surface is covered.

2. Pour-and-Roll Application:

  • The pour-and-roll application method involves pouring hot bitumen directly onto the roof surface and then rolling the bitumen-impregnated felt onto it.
  • The hot bitumen is typically poured from a heated container or kettle, ensuring it is evenly distributed over the roof surface.
  • The bitumen-impregnated felt is then rolled onto the hot bitumen, starting from one end of the roof and working towards the other.
  • Pressure is applied to ensure proper bonding between the felt and the bitumen as the felt is rolled out.
  • The process is repeated for each layer of felt, with overlaps adequately sealed and all areas of the roof surface covered.

Overlapping and Sealing for Felt Roof Installation

Overlapping and sealing the layers of felt is a critical step in installing a felt roof. Properly overlapping and sealing the felt layers ensures a watertight and durable roof. Here are the general steps for overlapping and sealing during felt roof installation:

  1. Determine the Overlap Distance: Check the manufacturer’s instructions for the specific felt roofing system you use to determine the recommended overlap distance. It typically ranges from 2 to 6 inches, depending on the product.
  2. Apply Bitumen Adhesive: Along the edge of the first layer of felt, apply a strip of bitumen adhesive or mastic using a trowel or brush. The adhesive should be spread evenly and cover the width of the overlap.
  3. Position the Next Layer: Roll out the next layer of felt onto the adhesive, ensuring it overlaps the first layer according to the recommended overlap distance. Carefully align the edges of the two layers.
  4. Press and Smooth the Overlap: Apply pressure to the overlapped area using a roller or hand tools to ensure good contact between the layers. This helps to create a secure bond and prevents water penetration.
  5. Seal the Overlap: Add additional bitumen adhesive or mastic over the overlapped area using a trowel or brush. Ensure that the adhesive is spread evenly and covers the entire overlap.
  6. Repeat the Process: Continue rolling out and overlapping subsequent layers of felt, repeating the same steps of applying adhesive, positioning, pressing, and sealing the overlaps.
  7. Overlap at Joints and Protrusions: Ensure that the overlaps are adequately sealed for areas where two sections of the felt meet, such as roof joints or around protrusions like chimneys or vents. As the manufacturer recommends, apply bitumen adhesive along the edges and use additional flashing or sealing materials.
  8. Inspect and Repair: Throughout the installation process, regularly inspect the overlaps for gaps, loose edges, or areas requiring additional sealing. Repair any damaged or poorly sealed sections promptly to maintain the integrity of the felt roof.

Finishing for Felt Roof Installation

After the main layers of felt have been installed and properly sealed, there are several finishing steps which can enhance the durability, weather resistance, and appearance of the felt roof. Here are some standard finishing options for felt roof installations:

  1. Protective Coatings: Applying a protective coating over the felt roof can provide additional protection against UV rays, weathering, and general wear and tear. There are various coating options available, such as acrylic or bitumen-based coatings. For proper application and curing time, always follow the manufacturer’s instructions.
  2. Mineral Granules: Sprinkling mineral granules onto the top surface of the felt roof can add texture, increase durability, and provide aesthetic appeal. The granules help protect the felt from UV damage and provide a more finished appearance. These granules are typically embedded into a layer of bitumen or adhesive to ensure they adhere securely to the roof.
  3. Reflective Coatings: Reflective coatings, often white or light-coloured, can help reduce heat absorption and lower the roof’s temperature. These coatings can improve energy efficiency by reducing cooling costs in warm climates.
  4. Edge Trims and Flashings: Installing edge trims and flashings can enhance the waterproofing and aesthetic aspects of the felt roof. Metal or PVC trims can create clean edges and protect vulnerable areas. Flashings seal roof junctions, chimneys, vents, and other roof penetrations.
  5. Roof Drainage Systems: Installing or ensuring the proper functioning of gutters, downspouts, and drainage systems is essential to prevent water buildup and facilitate effective water runoff from the roof. Adequate drainage helps prolong the lifespan of the felt roof and protects the underlying structure.
  6. Regular Maintenance: A regular maintenance schedule is essential to keep the felt roof in good condition. This includes removing debris, inspecting for damage or loose seams, and promptly performing necessary repairs.

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