How to Flash Sidewalls and Endwalls on Metal Roofs
Sidewall trim with a closure, endwall flashing under the wall cladding, and counter flashing where the wall is masonry or stucco.
- Advanced
- 3 to 6 hours for an average wall
- Updated
The short answer
On a metal roof, a sidewall (along the slope) gets a formed sidewall trim that runs up the wall behind the cladding, sits on the panel edge over a closure, and is fastened high on the wall leg. An endwall (across the top of the slope) gets a headwall flashing with a Z-closure, tucked under the wall's weather barrier. Stucco or masonry uses a counter flashing over the base flashing.
Where a metal roof meets a wall, water runs down the wall and across the roof at the same time and collects in the corner. On shingle roofs step flashing handles that. Metal panels do not step, so the flashing is a continuous formed trim that runs up the wall and sits on the panel, with a closure that seals the ribs. The principle is the same: the wall cladding goes over the flashing and the flashing goes over the roof.
Two conditions matter. A sidewall runs alongside the slope, so water runs along the trim toward the eave. An endwall or headwall runs across the top of the slope, so water running down the wall falls onto the roof above the trim, and the flashing has to lift it over the panels. Both need a closure under the trim and sealant where the trim meets the wall.
Metal roofs move more than shingles, so the trim has to allow for it. Read thermal movement in metal roofs. For shingle equivalents, see step flashing and headwall flashing.
Tools
- Sheet metal brake
- Aviation snips and hand seamer
- Flat bar for lifting siding
- Impact driver
- Chalk line and level
- Caulk gun
- Fall protection equipment
Materials
- Sidewall trim or flashing matched to the panel
- Endwall or headwall flashing
- Z-closure and profile closures
- Self-adhered membrane for the wall and deck
- Trim screws with washers
- Butyl sealant tape
- Counter flashing and a reglet or receiver for masonry and stucco
Safety first
- Wall junctions are often at the roof edge or beside a drop. Tie off and keep your feet on the roof, not on a loose panel.
- Lifting siding can release nails and cut-off pieces. Wear eye protection and gloves.
- WorkSafeBC requires fall protection at 3 metres (about 10 feet) and wherever a fall of any height could cause serious injury.
Step by Step
Step 1: Expose the wall and check what is behind the cladding
Lift the siding with a flat bar and look at the wall sheathing for stains, soft wood or old leak paths. Water damage behind the wall is common on roof to wall junctions. Repair any rot before flashing over it. Note the weather barrier: housewrap or building paper, which will lap over the top of the new flashing.
On stucco, you cannot lift the cladding, so the flashing needs a counter flashing set into a cut joint or a receiver. See cutting a reglet.
Step 2: Line the corner with self-adhered membrane
Fold the membrane so it lies on both surfaces, pressing it into the corner so there is no gap for a fastener or foot to puncture. Lap the main underlayment over the deck portion and the wall weather barrier over the top of the wall portion, so the layers shingle downwards. See metal roof underlayment.
Step 3: Install a closure along the wall edge
On a sidewall, the last panel stops short of the wall by the manual's gap, typically 1 to 2 inches, and the trim covers the gap. A closure under the trim keeps wind-driven rain, insects and snow out of the ribs. Use the closure shaped for the panel profile, sealed with butyl tape.
On an endwall, a Z-closure or flat closure runs across the top of the panels against the wall, and the flashing sits above it.
Step 4: Set the sidewall trim on the panel and fasten high on the wall leg
The roof leg of the trim is typically 3 to 4 inches wide and the wall leg 4 to 6 inches tall or more. Fasten the wall leg with a screw near its top edge, where the siding will cover it, at 12 to 24 inches. Fasten the roof leg through to the panel only as the manual specifies, usually along its outer edge with a screw through a slot, so the panel can expand beneath.
Lap sections 2 to 4 inches with the upper piece over the lower and butyl tape between. See metal roof screws.
Watch out: Do not fasten the roof leg rigidly to the panel and the wall leg to the wall. The roof and wall move independently and the trim will tear or ripple.
Step 5: Install the endwall flashing with a hemmed upper edge
The flashing has a horizontal leg over the top of the panels, sealed to the Z-closure, and a vertical leg up the wall. Fold the lower edge of the horizontal leg down into a hem so water drops clear of the panel ends. The upper edge goes under the wall's weather barrier or under the siding.
Extend the endwall flashing past the ends by a few inches and fold the end into a dam, so water running down the wall cannot run around the end of the flashing. See headwall flashing for shingles for the principle.
Step 6: Close the wall above: siding, stucco or counter flashing
Siding should stop a minimum of 1/2 inch to 2 inches above the roof surface, depending on the product, and not touch the panel. Lap the weather barrier over the wall leg. On masonry or stucco, fit a counter flashing into a reglet or receiver that covers the upper part of the trim. See counter flashing and flashing by cladding type.
Seal the top edge of counter flashing or a stucco receiver with a proper sealant, not caulk alone. See roofing sealants.
Step 7: Finish the ends and check for leaks
At the eave end of a sidewall, the trim turns out over the eave trim or ends in a kickout that directs water into the gutter. See eave trim and kickout flashing. At the ridge, the trim ends under the ridge cap.
Water test from the top down, and check inside the wall if you can. A wall leak can sit unseen for years.
Stucco and Masonry Walls
Stucco, brick and stone walls cannot be lifted, so the base flashing runs up the wall behind a counter flashing set into a cut reglet or a stucco receiver. The two pieces are not fastened together, so each can move. Seal the counter flashing top with sealant rated for the substrate. Breaking out stucco for a retrofit is rarely needed if the counter flashing is surface mounted with a sealed top edge.
Movement at Wall Junctions
A long sidewall trim on a dark roof can move noticeably. Steel expands about 0.78 inch over 100 feet with a 100 degree Fahrenheit swing. Use slotted fasteners or laps that can slide, and do not trap the trim between the wall and the panel.
Common Mistakes
- Fastening the trim to both the roof and the wall rigidly, so it tears as the two move.
- Leaving out the kickout at the bottom of a sidewall.
- Siding touching the panel, which wicks water and rots the boards.
- Missing the closure under the trim, so wind-driven rain enters the ribs.
- Caulking instead of lapping metal, relying on sealant alone.
- Flashing over rotten sheathing without repairing it.
- Ending the endwall flashing with no dam at the ends.
When to Call a Professional
Wall junctions are the place most roofs leak, and stucco and masonry need specialist detailing. If the wall is stucco, brick or stone, if the sheathing behind the siding is soft or stained, or if the wall sits above a steep or high roof, call a roofer.
A roofer will check the kickout, the headwall and the siding clearance in the same visit.
Fraser Roofing does free roof inspections across the Fraser Valley, from Hope to Abbotsford. See our Metal Roofing service or the towns we cover.
How to Flash Sidewalls and Endwalls on Metal Roofs: Questions
How do you flash a wall on a metal roof?
Run self-adhered membrane up the wall, set a closure along the wall edge, then fit formed trim with its roof leg on the panel and its wall leg running up behind the siding. Fasten the wall leg high, lap sections 2 to 4 inches and seal with butyl tape. At an endwall, use a Z-closure and headwall flashing.
What is the difference between sidewall and endwall flashing?
A sidewall runs alongside the slope, so flashing runs down the slope with water moving along it toward the eave. An endwall, or headwall, runs across the top of the slope, so water falls onto the roof above the flashing and the flashing has to lift it over the panels. Each needs a closure and a kickout or end dam.
What is counter flashing on a metal roof?
Counter flashing is a second piece of metal that covers the top of the base flashing where the wall is masonry or stucco. It is set into a cut joint or receiver in the wall, so the base flashing can move without breaking the seal. It is used instead of lifting siding, which is not possible on these walls.
How far should siding be above a metal roof?
Commonly between 1/2 inch and 2 inches above the panel surface, depending on the cladding and the manufacturer's requirement. The gap stops water wicking up the siding and lets debris clear. Fibre cement usually needs more clearance than vinyl. Check the cladding manufacturer's installation instructions.
Related Guides
All Metal Roofing guides|The full How-To Library
This guide is general education. Always follow the product manufacturer's installation instructions, the BC Building Code and WorkSafeBC requirements, which take priority over anything written here.
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