Properly overlapping roofing felt is crucial to ensure your roof is watertight and durable. Whether you’re laying felt on a shed roof, a flat roof, or a sloped structure, the overlap plays a key role in preventing water ingress and ensuring the felt stays secure. Here’s a guide on the minimum overlap requirements and best practices for installing shed roof felt.
1. Why Overlap Matters
Overlapping roofing felt creates a seamless and watertight barrier. Without sufficient overlap, water can seep between the layers, compromising the integrity of the roof and leading to leaks and damage.
2. Minimum Overlap Guidelines
When laying roofing felt, the overlap depends on the specific section of the roof:
- At the Eaves:
The first piece of felt should have an overlap of at least 40mm (4cm) at the eaves. This ensures water runs off the roof into the gutter or away from the structure. - Between Adjacent Pieces:
Adjacent pieces of roofing felt should overlap by 20cm (200mm) to provide a strong seal against water infiltration.
3. Installing Roofing Felt on a Shed Roof
Follow these steps for properly installing roofing felt with the correct overlap:
- Start at the Bottom Edge:
Begin by laying the first strip of felt along the lower edge of the roof, allowing it to overhang the eaves by approximately 40mm. Tack the felt securely along the front and back edges. - Work Your Way Up:
Place the next strip of felt above the first, ensuring a 20cm overlap between the two. This overlap prevents water from entering the seams. - Secure the Felt:
Use galvanized nails or tacks spaced evenly along the edges to secure the felt. Ensure the felt lies flat, with no gaps or wrinkles, to maintain a watertight seal. - Cap the Apex:
For pitched shed roofs, finish by laying a final strip of felt over the apex. This strip should extend equally down both sides of the roof, overlapping the top edges of the adjacent panels by at least 20cm.
4. Best Practices for Laying Roofing Felt
- Cut Felt to Fit: Use a utility knife to neatly trim the felt around edges, vents, or other protrusions.
- Use Adhesive (Optional): For additional security, apply adhesive along the edges and overlaps to reinforce the seal.
- Check Weather Conditions: Install roofing felt on a dry day to ensure proper adhesion and prevent moisture from getting trapped beneath the felt.
- Inspect Overlaps: Ensure all overlaps are consistent, with no gaps or misalignments.
5. Common Mistakes to Avoid
- Insufficient Overlap: Overlaps smaller than 20cm between adjacent strips can result in water seepage.
- Uneven Laying: Wrinkles or bubbles in the felt can compromise the watertight seal.
- Neglecting the Apex: Failing to secure the apex properly can allow water to pool or seep into the roof.
The minimum overlap when laying roofing felt is 40mm at the eaves and 20cm between adjacent pieces. Following these guidelines ensures a secure, watertight roof that protects your shed or other structure from the elements. By taking your time to align and secure the felt properly, you can extend the lifespan of your roof and avoid costly repairs in the future.
