Flashing is the quiet hero of a watertight roof. It is one of the essential elements of a weatherproof roofing system, ensuring that vulnerable areas are protected from water intrusion. It channels rain away from junctions and openings so water ends up in your gutters, not your ceiling. This guide explains where flashing goes, which tools and materials to use, and how to install the most common details on Australian roofs.

You will see short explanations followed by tight checklists so pros can scan and DIYers can follow along. This guide will help you achieve a successful roof flashing installation.

What Roof Flashing Does And Where It Goes

Flashing is a thin material, usually formed metal, that blocks water at vulnerable areas and roof features, such as chimneys, vents, dormers, and walls. Flashing acts as a barrier to prevent water infiltration and moves it back into the roof drainage path. You will find it wherever the roof surface meets a wall, exterior wall, or vertical wall, or where water concentrates around roof features.

Flashing acts to direct water away from vulnerable areas, ensuring water runs down and off the roof, which helps prevent leaks and water damage.

Areas That Require Flashing On Roof

Tools And Materials You Will Need

Set up before climbing a ladder. Most mistakes happen when people rush or cut metal in the wrong place.

Tools:

  • Tin snips, nibbler and a hand seamer or small folding brake
  • Tape measure, builder’s line, square and scribe
  • Drill or driver, pop riveter, roofing nails or class 4 screws with EPDM washers
  • Caulking gun with neutral cure silicone or roofing cement where specified
  • Butyl tape and flashing tape for laps and selective sealing
  • PPE: harness or edge protection, non slip footwear, cut resistant gloves, eye protection

Materials guidance:

  • Roof flashings are typically made from thin material such as galvanised steel, which is lightweight, flexible, and durable for weatherproofing. Most building codes specify a minimum thickness for flashing material to ensure compliance and long-term performance.
  • Match flashing metal and coating to the roof (Colorbond, Zincalume, aluminium where appropriate)
  • Separate dissimilar metals with a compatible barrier to prevent corrosion, and ensure flashing is separated from other building materials like brick or wood to avoid chemical reactions.
  • Use proprietary pipe boots for round vents
  • Detail every piece with positive fall to avoid ponding and debris build up
  • Select compatible roof materials and roofing materials, considering how building materials expand and contract with temperature changes. Proper sealing and fastening techniques help accommodate this movement and prevent leaks.
  • Common materials used for flashing include galvanised steel, aluminium, and rubber. Choose materials based on durability, compatibility with roof materials, and installation requirements.
Installing Flashing

Safety First On A Metal Roof

Pick a dry, calm day and plan your anchor points. Avoid walking on dusty or wet sheets. Isolate nearby electrical equipment before cutting metal and never use abrasive wheels that can burn protective coatings.

Safety checklist:

  • Edge protection or harness with a rated anchor
  • Soft soled, non slip footwear
  • Cut resistant gloves and eye protection
  • Tethered tools and clean work zone
  • Weather check and stop work limits
Damageed Vs Repaird Flashing

Core Rules For A Watertight Result

A few rules make the difference between a dry roof and a slow leak.

  • Install in shingle fashion so upslope pieces overlap downslope pieces, and ensure the first row of shingles is properly overlapped to provide effective waterproofing
  • Turn up corrugated pans 20 to 30 mm at the high side where the roof meets a wall
  • Lap metal by at least 100 mm and compress with butyl where required
  • Fix on crests, not in pans, at 200 to 300 mm centres
  • Add an anti capillary offset fold or leave a 3 to 5 mm clearance so water cannot wick
  • Make sure roof underlay drains to daylight, not into wall cavities
  • Use sealant to complete joints at terminations and penetrations, not to replace laps and upstands

Following these rules is crucial for preventing leaks and ensuring your roof remains protected from water damage.

Stormwater Runoff With Flashing

Underlay And Substrate Preparation At Walls And Chimneys

Before metal goes down, prepare the base. Dress a self adhesive waterproof membrane over the roof deck and continue it 100 to 200 mm up the wall surface and exterior wall. This ensures a sealed pan beneath the metal, helping to prevent water infiltration at the junction between the roof and wall. A waterproof membrane, such as an ice-and-water barrier, should cover the roof deck up to the base of the wall or chimney and extend 4–8 inches up the vertical surface before installing flashing. Always check the Building Code of Australia and supplier instructions.

Prep sequence:

  • Clean and dry the roof deck
  • Lay membrane on the deck and up the wall surface and exterior wall 100 to 200 mm to prevent water infiltration
  • Mark reference lines for laps and fixings
  • Dry fit the metal pieces before you fasten

Apron Flashing Installation At A Roof To Wall

Apron flashing protects the junction where the roof surface meets cladding or masonry. Start with clean bends and a firm dry fit. Then fix methodically and finish with counter flashing.

How to do it:

  1. Measure And Pre Form – Upstand should be installed behind wall cladding 100 to 150 mm; cover over roof sheet at least 100 mm.
  2. Dry Fit And Mark Laps – End laps 100 mm minimum with butyl tape.
  3. Turn Up The Pans – Corrugated turn ups 20 to 30 mm at the high side.
  4. Fix The Lower Edge – Fix through crests at 200 to 300 mm centres; never through pans.
  5. Add Counter Flashing – Masonry Reglet chase 20 to 25 mm; or termination bar on cladding. Keep a weep path.
  6. Seal Selectively – Use a caulking gun to seal chases and mitres. Do not block drainage.
  7. Hose Test – Hose from low to high and check for back flow.

Step Flashing And Counter Flashing Against Masonry Or Cladding

Following a step by step process is essential for proper installation of step flashing and counter flashing.

Where a wall meets a pitched, shingled surface, step flashing is reliable, forgiving and proven.

Key points:

  • Installing flashing correctly is critical for waterproofing—cut L shaped steps about 200 mm long with a 75 to 100 mm vertical leg
  • Weave each piece between shingle courses with 100 mm head laps in the flow direction
  • Install a kickout flashing at the base to push water into the gutter
  • Finish with counter flashing chased 20 to 25 mm into mortar or fixed with a termination bar on cladding
  • Fix counter flashing to the wall only so the roof can move with temperature

How To Install Flashing On Corrugated Roof Penetrations

Chimneys, skylights and vents collect water and demand careful sequencing. The back pan does the heavy lifting as the base flashing for the penetration; side and head pieces complete the roof flashings system.

Penetration sequence:

  • Back pan, serving as the base flashing, extends at least 150 mm past each side of the penetration
  • Head of back pan tucks under counter flashing by 75 to 100 mm
  • Turn ups 20 to 30 mm at the upslope edge; turn down the lower edge
  • Side pieces overlap the back pan 100 mm with butyl tape
  • Fix on crests at 200 to 300 mm centres
  • Round vents use a profiled base and a storm collar sealed to the pipe, not the sheet
  • Metal forms the structure; sealant at collars and chases completes a neat watertight finish

Barge And Valley Flashing Basics

Barge flashing protects the gable edge from wind driven rain and finishes the profile neatly. Overlap lengths by at least 100 mm, fix on crests and use hemmed edges to stiffen the metal and reduce flutter.

At roof cladding edges located away from gutters, a cover flashing fastened on both faces is required to ensure proper weatherproofing and to prevent water ingress.

Valley flashing is the internal gutter where two roof planes meet. Size it for your rainfall and roof area, keep the path clear of debris and maintain steady fall to the gutters.

Quick specs:

  • Barge overlaps 100 mm minimum; hemmed edges preferred
  • Valley sized to catchment and intensity; clear of debris; positive fall to gutter

How To Install Gutter Flashing And Drip Edge

Eaves are a common leak point when water tracks behind the fascia. The drip edge stops that.

Do this:

  • Overhang the drip edge 10 to 15 mm into the gutter
  • Cover the fascia 20 to 25 mm to protect the timber
  • Fix on a crest or stiffened edge at 200 to 300 mm centres
  • Check that underlay and sheets discharge over the drip edge without back wicking

Sill, Jamb And Head Flashing Around Openings

Sequence is everything around openings. It keeps water moving outwards even if wind pushes rain behind cladding.

Correct order:

  • Sill Flashing First forms a pan that projects beyond the cladding
  • Jamb Flashings Next overlap the sill and channel water downward
  • Head Flashing Last sheds water over the jambs with a drip edge and end dams

Fasteners, Sealants And Compatibility In WA Conditions

Coastal and sub coastal WA needs extra care. Choose fixings and sealants that last and keep dissimilar metals apart.

Recommendations:

  • Class 4 self drilling screws with EPDM or neoprene washers
  • Neutral cure silicone at terminations; butyl tape in laps, applied neatly with a caulking gun. Using sealant to securely attach flashing is essential for effective waterproofing.
  • Keep copper away from Zincalume and Colorbond or separate with a membrane
  • Allow for thermal movement on long runs and avoid over fixing

For complex situations, installing roof flashing should be done by professional roofers to ensure safety and long-term performance. It is essential to confirm that the installation methods comply with local building codes during flashing installation.

Common Mistakes And How To Avoid Them

Improperly installed roof flashing is one of the most common causes of leaks and water damage. Most leaks come from small errors rather than bad materials.

Watch for:

  • Reverse laps that drive water upslope and behind metal
  • Fixing through pans instead of crests
  • Under bending aprons so they spring away from cladding
  • Blocking weeps under counter flashing
  • Relying on sealant as the primary waterproofing
  • Abrasive cutting that burns protective coatings

Quick Checklist Before You Leave The Roof

  • Upstand 100 to 150 mm at roof to wall; cover over sheet at least 100 mm
  • Turn ups 20 to 30 mm at corrugated high sides
  • End laps 100 mm minimum, compressed with butyl
  • Fixings on crests at 200 to 300 mm centres with sound washers
  • Anti capillary fold or 3 to 5 mm clearance on edges
  • Drip edge overhang 10 to 15 mm and fascia cover 20 to 25 mm
  • Underlay dressed up walls 100 to 200 mm where required

Frequently Asked Questions

Flashing is thin, formed metal that directs water away from joints and openings so the building stays weatherproof. It prevents leaks at roof to wall junctions, chimneys, valleys, skylights and around windows and doors.

Common options are galvanised or pre painted steel, aluminium and copper, plus proprietary rubber or PVC boots for round penetrations. Match metals to the roof and separate dissimilar metals to prevent corrosion.

Install flashing wherever the roof plane meets a vertical surface or where water concentrates, including valleys, chimneys, vents, skylights, barge edges, eaves and along roof cladding edges away from gutters.

Yes. Fit sill flashing first to form a pan, then jamb flashings that overlap the sill, and finish with head flashing that sheds water over the jambs with a clear drip edge and end dams.

Basic drip edges and short aprons can be DIY if you follow supplier instructions and safety rules. Chimneys, parapets, complex valleys and low pitches should be installed by a professional roofer.

Reverse laps, small upstands, blocked weeps or fixing through pans let water track behind the metal. The result is stains, rot and mould. Chimneys fail often when base and counter flashing are not sequenced correctly.

Look for water stains after rain, damp insulation, rusted or lifted edges and drips at roof to wall junctions. Outside, a missing kickout flashing at the base of a wall is a common red flag.

Replace flashing that is rusted, deformed, poorly lapped or no longer seats tightly against cladding. Inspect twice a year and after storms, and plan replacement during roof restorations or re roofing.

You will need tin snips, a nibbler or hand seamer, a drill or driver, a pop riveter, a tape and square, class 4 screws with EPDM washers, butyl tape and a caulking gun with neutral cure silicone.

Step flashing uses individual L shaped pieces woven between shingle courses along a wall. Continuous flashing, also called apron flashing, is a single length used at roof to wall junctions or against cladding.

Book Professional Flashing Installation

If you want a neat, compliant result that stays watertight through Perth conditions, Fremantle Roofing Services can help. We fabricate and install apron flashing, step flashing, chimney flashings, valley flashing and gutter flashings to suit your roof profile and the Building Code of Australia. Contact Fremantle Roofing Services for an inspection and quote today.

Adam Dean

Adam has 28 years of roof tiling and restoration experience, he has been running Fremantle Roofing Services since its inception and is still trying to improve the business and its reputation. Adam has worked on everything, Often a little grumpy before 10 am but otherwise always happy to discuss the job and explain exactly what’s going right or wrong with your roof.