How to Install Roof Flashings Step by Step
Key summary
- Goal: Make the roof watertight by correctly installing roof flashings at joints, valleys, ridges and wall junctions.
- Best materials: Colorbond steel flashings sized to suit your roof profile.
- Fixings: Roofing screws or rivets at 200 to 300 mm spacing, with minimum 100 mm overlaps.
- Seal: Use roofing grade neutral cure silicone or butyl tape on all laps and penetrations.
- Cutting: Use tin snips or a nibbler. Avoid angle grinders to protect the Colorbond coating.
- Safety: Work on dry days, use fall protection, gloves and eye protection.
- Pro tip: Custom flashings sized correctly reduce on-site cutting and speed installation.
What are roof flashings
Roof flashings are thin, formed metal sections that direct water away from vulnerable areas and into the guttering system. They seal transitions such as roof edges, valleys, abutments and ridgelines so wind driven rain cannot enter the roof cavity.
Common types of roof flashings
- Barge flashings: Finish and protect roof edges.
- Valley flashings: Channel water where two roof planes meet.
- Apron flashings: Seal where a roof meets a vertical wall or chimney.
- Ridge flashings: Cover and protect the ridge at the top of the roof.
Tools and materials for installing roof flashings
- Tape measure and chalk line
- Tin snips or nibbler
- Drill and rivet gun
- Roofing screws or rivets with washers
- Neutral cure roofing silicone or butyl sealing tape
- PPE: gloves, eye protection and fall protection
- Pre cut or custom Colorbond roof flashings
Note: Using snips or a nibbler preserves the Colorbond finish and reduces swarf. Avoid angle grinders where possible.
Before you start: plan and measure
- Check the roof profile so your flashings match the sheet type and pitch.
- Measure all runs and add allowance for overlaps. Mark cut lines with a chalk line.
- Dry fit each piece on the roof to confirm coverage and water flow direction.
- Clean the surface so sealant bonds correctly and remove any swarf after cutting.
How to install roof flashings
Step 1. Measure and cut to size
Measure the length required. Add allowance for a minimum 100 mm lap where pieces will join. Cut with tin snips or a nibbler for clean, burr free edges.
Step 2. Position the flashing
Place the flashing so the upper edge sits under the roofing sheet or cladding where required, and the lower edge discharges into the gutter or over the lower sheet. Check the fall so water cannot pond.
Step 3. Fix into place
Starting from one end, fasten at 200 to 300 mm spacing. Keep fixings straight and avoid over tightening which can distort the profile or squash washers. Work across the length to prevent buckling.
Step 4. Seal joints and overlaps
Where flashings join, provide a minimum 100 mm overlap. Apply a continuous bead of roofing grade neutral cure silicone or use butyl sealing tape between layers. Tool the sealant for full edge contact.
Step 5. Finish and inspect
Ensure the flashing sits tight against the surface with no gaps. Seal any visible pinholes. Remove all swarf to prevent tea staining. Touch up cut edges with manufacturer approved paint if specified.
Pro tips for a neat, watertight finish
- Choose Colorbond flashings to match your roof for long life and a clean finish.
- Install only in dry conditions so sealants cure as intended.
- Do not over tighten screws or rivets. Compress the washer just enough to seal.
- Use custom made flashings for unusual junctions to avoid patchwork seams.
DIY or hire a roofer
Confident DIYers can handle straightforward installations. For complex junctions, steep pitches or long runs, a licensed roofer is recommended to avoid costly leaks.
Order custom flashings online
Need exact sizes or special profiles
- Design online and see live pricing
- Choose from the full Colorbond colour range
- Order for Australia wide delivery or Click and Collect
Start your design in the ClickSteel Flashings Designer.
Frequently asked questions
How much overlap do I need on roof flashings
Allow at least 100 mm. In high wind or heavy rain zones consider greater laps as per local standards.
What sealant should I use
Use a neutral cure roofing silicone compatible with Colorbond or a butyl sealing tape under laps.
Should I screw or rivet flashings
Both are common. Use roofing screws with washers for easy removal and adjustment or sealed rivets for a low profile finish.
Can I cut Colorbond flashings with a grinder
Avoid it. Use tin snips or a nibbler to protect the coating and reduce swarf.