Laying a felt roof is a practical, cost-effective option for sheds, outbuildings, and extensions. This guide walks through the key steps, materials, and best practices to ensure a durable, weather-tight membrane. By following a methodical process for laying a felt roof, homeowners can achieve reliable protection against rain and wind while extending the life of their structure.
Preparation And Safety
Before starting, inspect the roof deck for damage, rot, or loose boards. Replace any compromised sections to ensure a stable surface for laying the felt. Clean the roof thoroughly, removing dust, debris, and loose nails. Work on a dry day with stable footing, using a sturdy ladder and, if needed, a safety harness. Wear gloves and eye protection when handling roofing materials and nails. Proper preparation reduces the risk of leaks and makes the installation smoother.
Materials And Tools
A successful laying of a felt roof depends on selecting the right components and having the proper tools. Common materials include:
- Roof felt rolls (asphalt- or bitumen-based, with or without glass fiber reinforcement)
- Underlayment or membrane starter strips
- Roof nails or nails with plastic caps
- Bitumen-based flashing and sealant
- Fiberglass or mineral-surfaced felt caps (if required by local code)
- Overlapping battens (if used on certain substrates)
- Roofing cement or adhesive (per manufacturer instructions)
- Measuring tape, utility knife, chalk line, and a straightedge
Having these tools ready helps prevent mid-project delays. A typical set also includes a hammer, roofing trowel, brush or roller for adhesive, and a sledge for driving nails where needed.
Substrate Preparation
Lay down a clean, smooth surface under the felt to ensure proper adhesion and even coverage. If the roof deck is plywood or oriented strand board (OSB), check for moisture and repair any warped panels. Sand rough patches and remove protrusions that could puncture the felt. Install a roof underlayment if recommended by the felt manufacturer, especially on exposed exposures or steep pitches. Proper substrate preparation reduces the risk of leaks and extends the roof’s service life.
Underlay And Starter Strips
Begin with a starter strip along the eaves to control the first course’s alignment and prevent water from seeping under the edges. The starter strip should be cut to length and positioned so that the upper edges align with the intended fanning or covering pattern. If using an underlayment sheet, apply it per the manufacturer’s instructions, ensuring it overlaps edges and is securely fixed. This layer provides an additional barrier against moisture and helps the main felt layers lay flat without wrinkling or air pockets.
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Applying The Felt
Roll out the first course of felt starting at one eave and working upward. Align the roll with a straight edge as you unroll to avoid creases. Secure the felt with nails along one edge or through the center of the sheet, following the manufacturer’s nail pattern. For stronger installations, stagger the joints between courses so that seams do not align along the same vertical line. Each course should overlap the one below by a consistent amount, typically about 75 mm (3 inches) for standard asphalt felt, or as specified by the product. Thermally activated asphalt felts may require heat or adhesive setting; follow the specific instructions for your product.
Edge Sealing And Ventilation
Seal all edges, hips, and ridges to prevent wind uplift and water ingress. Use asphalt roof cement or the manufacturer’s recommended sealant at joints and edges. Apply flashing at valleys, parapets, and any protrusions like chimneys or vents, ensuring a tight seal with the felt and base materials. Proper ventilation beneath the roof helps prevent condensation and extends the life of the membrane. If the roof is steep, extra attention to securement and overlap is crucial to resist uplift during high winds.
Seaming, Nailing, And Overlaps
Ensure that all seams are properly lapped and sealed. When nailing, drive nails through the felt at regular intervals and place nails at the recommended distance from the edges to avoid tearing. For larger roofs or higher wind zones, additional mechanical fasteners or sealant beads may be required. Do not over-tighten nails, which can cause the felt to tear. Regularly check overlaps to ensure continued protection as the roof ages. Proper seaming reduces the risk of moisture ingress and improves overall durability.
Flashing And Penetrations
Flashing around vents, chimneys, and skylights must be installed with care. Cut the felt to create a tight fit against the flashing material, then seal with compatible flashing cement or adhesive. Use backer rod or similar materials behind flashing if needed to maintain a watertight seal. For chimney and vent flashings, ensure slopes direct water away from joints and towards the exterior surface. Poor flashing is a common source of leaks, so it warrants careful attention during the laying process.
Inspections And Maintenance
After installation, inspect the roof for any loose edges, wrinkles, or misaligned seams. Push or re-nail any sections that have come loose, and apply additional sealant where necessary. Periodic maintenance is essential; check after heavy rain, windstorms, or freezing temperatures when materials expand and contract. Clean debris from the roof and ensure drainage paths remain clear. A well-maintained felt roof provides reliable protection for many years with appropriate care.
Common Pitfalls To Avoid
- Not allowing for adequate overlap, which can lead to leaks at seams.
- Rushing the nailing process, causing loose sheets or tears.
- Ignoring substrate defects, resulting in premature failures.
- Improper flashing, which remains a leading cause of water intrusion.
Frequently Asked Questions
- How long does a felt roof typically last?
- What is the best overlap for felt roofing?
- Can felt roofs be repaired on the same day?
Note: Always follow the specific manufacturer instructions for the felt product you choose, as recommendations on overlaps, nailing patterns, and sealing compounds can vary. Local building codes may also influence acceptable methods for laying a felt roof in different climates.