To cut roofing felt on a roof effectively, you primarily need to make precise cuts to fit the roof dimensions, ensure proper overlap, and trim excess material. This process usually involves measuring and cutting rolls of roofing felt into manageable lengths before they are fully secured.
Essential Tools for Cutting Roofing Felt
Having the right tools is crucial for clean, accurate, and safe cuts.
- Utility Knife / Roofing Knife: A heavy-duty utility knife with retractable, replaceable blades is essential. Specialized roofing knives often have a hooked blade for easier cutting through thick felt.
- Tape Measure: For accurate measurements of roof length and width, as well as felt overlap.
- Straightedge / Chalk Line: A long straightedge (e.g., a 2x4, metal ruler) or a chalk line helps ensure straight cuts across the felt.
- Scissors / Shears: Useful for intricate cuts or trimming smaller pieces.
- Gloves: To protect hands from rough edges and potential cuts.
- Safety Glasses: To protect eyes from debris.
Preparing to Cut Roofing Felt
Before making any cuts, proper preparation ensures a smooth installation process.
Measuring and Initial Cuts
Begin by measuring the full length of your roof from front to back. Cut the roofing felt into lengths that will cover this dimension, ensuring each piece is approximately 10cm longer than the actual length of the structure. This extra length allows for overhang at the eaves and ensures complete coverage.
Ensuring Proper Overlap
When laying felt, especially at the eaves (the edges of the roof that overhang the walls), you want to aim for about a 40mm overlap. This overlap helps create a drip edge, directing water away from the fascia and walls of the structure.
Step-by-Step Cutting and Installation
Follow these steps for effective cutting and installation of roofing felt.
- Unroll and Position the First Piece:
- Unroll your first pre-cut length of roofing felt along one edge of the roof, typically starting at the lowest point (eaves) and working upwards.
- Align the edge carefully, ensuring the 40mm overlap at the eaves.
- Place the first piece at one edge and tack the front and back to hold it temporarily in position. This prevents the felt from shifting while you work.
- Secure the Felt:
- Once positioned and lightly tacked, fully secure the felt using appropriate fixings like clout nails or roofing felt adhesive, following the manufacturer's instructions. Work from the center outwards, pulling the felt taut to avoid wrinkles.
- Trim Excess at Eaves and Gable Ends:
- After the felt is securely attached, use your utility knife with a straightedge to carefully trim any excess felt at the eaves and gable ends. The goal is a neat, straight edge that aligns with the roof's drip edge or fascia.
- For a clean cut, press down firmly on the felt with your straightedge and draw the knife along it in one continuous motion.
- Overlapping Subsequent Layers:
- For subsequent rows of felt, you will need to overlap the previous layer. This creates a waterproof seal. The typical overlap is 50-75mm (2-3 inches).
- Measure and mark the overlap line on the installed felt to ensure a consistent, straight line for the next piece.
- Cutting Around Obstacles (if any):
- If your roof has obstacles like vents or chimneys (more common on larger roofs than sheds), cut the felt to fit around them.
- Measure the dimensions of the obstacle and transfer these measurements to the felt.
- Make relief cuts (diagonal cuts towards corners) to allow the felt to wrap snugly around the base of the obstacle.
- Use mastic or sealants around these areas for a watertight finish.
Roofing Felt Cutting Guidelines
| Aspect | Recommendation | Purpose |
|---|---|---|
| Length | 10cm longer than roof length | Allows for overhang at eaves and proper trimming. |
| Eaves Overlap | Approximately 40mm | Creates a drip edge to divert water. |
| Layer Overlap | 50-75mm (2-3 inches) | Ensures a watertight seal between felt layers. |
| Tools | Utility knife, straightedge, tape measure | For precise and clean cuts. |
| Method | Cut felt before full installation for main lengths | Easier to handle and cut accurately on the ground or a flat surface. |
Tips for Clean, Straight Cuts
- Sharp Blade: Always use a new, sharp blade in your utility knife. Dull blades tear felt and make uneven cuts.
- Firm Pressure: Apply firm, consistent pressure on the knife and straightedge.
- Work on a Stable Surface: When cutting full lengths, use a flat, stable surface like a plywood sheet or the roof deck itself if it's clear.
- Mark Your Lines: Use a chalk line or pencil to clearly mark your cutting lines before you start.
- Cut from the Back: Sometimes, cutting from the back (underside) of the felt can provide a cleaner edge, especially if the top has a granular finish.
- Safety First: Always cut away from your body and keep fingers clear of the blade path.
For more detailed guides on shed roofing felt installation, you can consult resources like Wickes' guide to shed felt roofing or general DIY roofing tutorials.
