A homeowner in Coquitlam calls about a brown stain on the living-room ceiling, a metre in from the exterior wall, under the spot where the garage roof meets the two-storey wall above it. The roofer who replaced the shingles two years ago comes back, finds nothing wrong with the roof, and leaves. The siding contractor says the siding is fine. Both are right about their own trade. The water is coming in at the line between them.
That line fails more often than any other single detail on a BC wall. A roof-to-wall flashing leak in BC rarely shows itself where the water enters. It runs down inside the wall and appears as a ceiling stain, a soft baseboard, or a patch of stucco that darkens after rain and takes days to dry.
Why does roof-to-wall flashing leak in BC?
Roof-to-wall flashing leaks when water running down a roof slope reaches the wall and nothing turns it back onto the roof or into the gutter. The three usual causes are a missing kickout diverter at the bottom of the junction, step flashing that is too short or sealed with caulk instead of lapped, and cladding run down onto the roof so it traps water behind it. On a BC house that takes 1,200 to 2,500 mm of rain a year, any one of the three puts litres of water into the wall every storm.
The three parts, and what each one does
Three pieces of metal handle the junction between a sloped roof and a wall.
Step flashing is a row of L-shaped pieces, one for every shingle course, each bent to sit about 75 mm up the wall and 75 mm out onto the roof. Each piece laps over the one below by the same 75 mm, so water that gets under a shingle lands on metal and runs down to the next piece. Part 9 of the BC Building Code sets those minimums where a shingle roof meets a wall. The leg that runs up the wall sits behind the building paper or house wrap, so anything reaching the wall face drains down over the metal, never behind it.
Counterflashing is the second piece. On a stucco or masonry wall it is a strip of metal that comes down over the top of the step flashing from behind the cladding and covers the joint. On siding, the cladding itself often does this job, held 25 to 50 mm clear of the roof surface so the cut edge can dry.
The kickout is the piece that gets left out. At the bottom of the junction, where the eave ends and the wall continues down, the last piece of step flashing has nowhere to send its water. A kickout is that last piece bent outward into a small scoop that throws the water into the gutter. Without it, every drop that ran the full length of the step flashing lands on the wall below the eave and runs down behind the siding or stucco.
A 6 m run of roof sheds roughly 250 litres onto that one corner in a 40 mm rain day. On a west-facing wall in North Vancouver, that happens many times a winter.
Where water gets in
Missing kickout. A vertical stain or a stripe of algae on the wall directly below the end of an eave is the signature. On stucco, the finish stays dark after everything around it has dried. Behind it, the sheathing at that corner is usually the first wood in the house to rot. We see it on 1990s houses in Coquitlam, Port Moody and Surrey, and on strata townhouse rows where the same detail repeats at every unit.
Step flashing too short, or not stepped at all. Some reroofing crews run one continuous L of metal along the junction instead of individual pieces, then seal the top edge with caulk. The caulk lasts two to five years. The leak that follows looks like a roof leak, and the roof is new, so nobody suspects the flashing.
Reverse lap. The building paper on the wall should lap over the top of the step flashing. When the roofer tucked the metal over the paper instead of under it, water running down the wall gets behind the flashing. This happens on roofs replaced after the wall was built, which describes most reroofs.
Stucco or siding buried in the roof. Stucco carried down to touch the shingles has no way to drain and wicks water up from the roof surface. BC envelope practice calls for the cladding to stop 50 mm above the roof, with a drip edge or casing bead at the bottom so the stucco can weep. A stucco edge sitting on the shingles is a leak waiting for the next storm.
Chimney and dormer walls. A chimney on the downslope side of a roof needs a saddle behind it, a small peaked flashing also called a cricket. Dormer side walls are short roof-to-wall junctions with their own kickouts. Both get missed on retrofits.
Our guide to where BC envelopes leak during atmospheric river season covers the other usual entry points, and the piece on wind-driven rain explains why the same detail fails on one elevation and holds on another.
Reading the symptoms
Inside: a ceiling stain near an exterior wall, below the point where a lower roof meets the upper wall. A baseboard that swells. Paint bubbling at a wall-ceiling corner. A window under the junction with a stained head trim.
Outside: a tide mark on the wall under an eave end, moss in a stripe, stucco cracks radiating from the junction, siding that has cupped or gone soft when pressed. On a strata building the pattern repeats at the same corner of every unit, which means the original detail was built that way along the whole row.
A moisture meter through the wall below the junction confirms it. Readings above 20 per cent in sheathing mean the wood has been wet for a while. Our article on testing stucco for moisture explains what probe readings tell you.
The mistake homeowners make here is to caulk the junction. Caulk over the top of flashing or along the stucco-to-roof joint holds water in and hides the problem until the sheathing is gone.
What the repair involves
A flashing repair at a roof-to-wall junction starts with the cladding. The siding or stucco next to the junction comes off far enough to expose the building paper and the top of the step flashing, usually 300 to 600 mm up the wall. Rotten sheathing gets cut out and replaced. The house wrap or paper is lapped correctly over new step flashing, the kickout goes in at the bottom, and the cladding goes back with the right clearance.
On a house with siding, a kickout retrofit with sound sheathing behind it is typically a one-day job for a two-person crew, in the range of $800 to $2,500 per location depending on height and access. On stucco the finish has to be cut, patched and colour-matched, and the price moves to $1,500 to $4,000. Where sheathing and framing have rotted, the opening grows, and a single corner can run $5,000 to $25,000 once structural repair, drying and interior finishes are counted.
Cutting into stucco pays for itself when it is done once and properly. Our stucco and EIFS crews handle the cutting, lath and patching, and our building envelope team scopes the flashing and wrap behind it, so the junction is rebuilt as one assembly. On a strata building with the detail repeated along a row of units, shared scaffolding and the same repair sequence at every unit are where the money is saved.
The insurance question
Most BC home policies cover sudden and accidental water damage and exclude gradual seepage and faulty workmanship. A roof-to-wall leak that has been working for three winters is usually the second kind. A windstorm that tears the flashing loose and floods the wall in one night is the first, and that claim tends to go through.
Call your broker before you decide the claim is hopeless. Resulting damage to interior finishes is sometimes covered even when the flashing repair itself is not, and the adjuster will want photos, moisture readings and a written scope. Keep the flashing repair and the interior restoration on separate invoices.
Houses under ten years old carry 2-5-10 home warranty coverage in BC, and the building envelope falls under the five-year term. A flashing defect on a house built in 2022 is a warranty claim first.
On a strata, the roof and the exterior walls are common property. The owner reports the stain to the property manager and the strata corporation arranges the investigation. Our piece on water ingress in a BC strata sets out who pays for what.
What happens when
First 24 hours. Photograph the stain inside and the wall outside. If water is dripping, catch it and move furniture. Do not caulk anything. If a storm tore flashing loose and the wall is open, temporary cover goes on the same day; our article on storm and wind damage repair covers emergency protection.
First week. A site visit, a hose test at the junction with someone inside watching, and moisture readings down the wall below it. Where readings are high, a section of cladding comes off to show the sheathing. The written scope follows from that opening, not from the stain.
Full repair. One junction with sound framing: one to three days. A rotted corner with sheathing, framing and interior finishes: one to three weeks, longer in winter when stucco and sealants need temperatures above 5°C. A strata row with the same defect at twelve units: six to twelve weeks with scaffolding, usually booked for the dry season.
Who should open the wall
MV Construction has repaired roof-to-wall junctions on houses and multi-family buildings across Greater Vancouver and Vancouver Island for 17+ years. We are fully licensed and WCB-insured, our crews take emergency calls within Greater Vancouver, and every flashing and cladding repair on our exterior renovation work carries a written warranty.
If a stain has appeared below a roof corner, call (778) 375-5672 or request a free written estimate. We find where the water gets in before we price the repair, and the scope, price and timeline go on paper before work begins.
