The Short Answer
Sidewall and dormer leaks usually come from the metal at the roof-to-wall joint: step flashing that was reused, cut short or reverse lapped, a missing kickout flashing at the bottom of the wall, or counterflashing on brick that has pulled loose. Just as often the water enters higher up, through siding, trim or a window, runs down behind the siding and appears at the roofline, so it looks like a roof leak when it is a wall leak.
Key Points
- The Michigan Residential Code requires base flashing at least 4 inches high and 4 inches wide at a sidewall, tucked under the siding.
- A kickout (diverter) flashing at the bottom of the wall is required by code and is the piece most often missing.
- Stains below the roof-to-wall line, rot in the wall under the eave, or leaks only in wind-driven rain all point to this joint.
- If water is entering above the roofline through siding or windows, new roof flashing will not stop it.
- A proper repair replaces the step flashing with new metal; reusing old step flashing is a common cause of repeat leaks.
How a Roof-To-Wall Joint Is Supposed to Shed Water
Where a roof slope runs up beside a wall, each course of shingles gets its own L-shaped piece of metal called step flashing. One leg lies on the shingle, the other runs up the wall, and the next shingle covers the roof leg. Each piece overlaps the one below it, like the shingles themselves, so water stepping down the wall is handed from piece to piece and back onto the roof.
The wall leg has to sit behind the siding and behind the wall's water-resistive barrier (the housewrap or felt). That is what makes the joint work: water running down the face of the wall stays outside the metal, and water that gets behind the siding is carried out over the metal instead of into the framing.
At the bottom of the wall, where the roof edge ends and the wall keeps going, a kickout flashing turns the water out into the gutter or onto the roof. Without it, every drop that came down the wall is dumped into the corner where the fascia, the siding and the wall framing meet.
Step flashing
One piece per shingle course
L-shaped metal woven into the shingles along a sloped sidewall. Overlapping pieces step water down the wall and back onto the roof.
Kickout (diverter) flashing
Bottom of the wall
A bent piece at the eave end of a sidewall that throws water away from the wall and into the gutter. Code requires one; many older roofs have none.
Counterflashing
Brick, stone, stucco
A second layer that covers the top of the step flashing where the wall is masonry or plaster and the metal cannot simply tuck behind siding.
Headwall (apron) flashing
Front of a dormer
A continuous piece where the top of a roof slope dies into a wall, such as the face of a dormer or a second story above a porch roof.
Our flashing repair serviceWhat the Michigan Residential Code Actually Says
Michigan builds to the 2015 Michigan Residential Code, which is based on the 2015 International Residential Code. Section R903.2.1 requires flashing at wall and roof intersections and adds that a flashing shall be installed to divert water away from where the eave of a sloped roof meets a vertical sidewall. That second sentence is the kickout requirement. Metal flashing must be corrosion resistant and not less than 0.019 inch thick (No. 26 galvanized sheet).
Section R905.2.8.3 covers asphalt shingle roofs specifically. Base flashing against a sidewall must be continuous or step flashing, not less than 4 inches high and 4 inches wide, and must direct water onto the roof or into the gutter. Where there is siding, the vertical leg must run continuously under it. Where the wall is brick or stone veneer, counterflashing is also required.
Shingle manufacturers can ask for more than the code. GAF's installation instructions for its Timberline shingles call for step flashing that extends 5 inches over the shingle and 5 inches up the wall, two nails per piece into the deck (not the wall), pieces lapped 2 inches, leak barrier membrane run at least 5 inches up the wall, and siding held at least 2 inches above the roof surface while covering the flashing by at least 2 inches. Beyond those minimums, the craft of flashing a wall well is mostly learned on the roof rather than from a manual.
How Sidewall and Dormer Flashing Fails
Very little of this is the metal wearing out. Galvanized or aluminum step flashing that was installed right often outlasts the shingles. Most sidewall leaks trace back to how the joint was built, or to what happened to it during a later reroof or siding job.
- Reused step flashing. On a reroof, the old pieces get bent back and reused to avoid touching the siding. They are often bent, nail-holed and the wrong length for the new shingle exposure, and they leak.
- No kickout. Water from the whole wall runs into the eave corner and soaks the wall framing and sheathing below it.
- Short or unlapped pieces. Step flashing has to overlap the piece below it (GAF calls for 2 inches) and reach past the shingle above. Pieces that are too short leave a gap at every course.
- Flashing installed on top of the housewrap, or siding installed tight to the roof. Water running behind the siding gets behind the metal, or the siding wicks water and holds debris against the shingles.
- Caulk doing the metal's job. A bead of sealant along the top of the flashing or the siding edge works for a season or two, then cracks with freeze-thaw and UV.
- Loose or surface-mounted counterflashing on brick. Metal that is caulked to the face of the masonry rather than set into a cut joint pulls away as the mortar and sealant age.
- Dormer corners. The two front corners of a dormer, where the headwall meets the sidewalls, need folded or soldered corner pieces. A gap there is a classic small, stubborn leak.
Water Behind Siding: When It Is Not a Roof Leak at All
The code expects every exterior wall to have a water-resistive barrier behind the siding and a way to drain water that gets past the siding back out. Siding is a rain screen, not a waterproof skin. Water gets behind it at window and door trim, at J-channel, at light fixtures and hose bibs, and at loose or cracked pieces.
If that water reaches the roof-to-wall line and the wall's barrier is lapped correctly over the step flashing, it runs out over the metal and does no harm. If the barrier is missing, torn, or tucked behind the flashing instead of over it, the water ends up inside the wall or on top of the roof deck. From inside the house it looks exactly like a roof leak.
The tell is where and when it leaks. A wall leak tends to show up in the wall cavity, around a window below, or at the base of the wall, and it often follows rain driven against that face of the house. A roof leak at the joint shows up on the ceiling or the attic side of the wall and is more likely to follow heavy rain on the roof itself or snowmelt.
- Step 1
Look Above the Roofline
From the ground, check the wall above the roof joint for windows, vents, light fixtures, cracked siding or open trim joints. Anything that can take water in sits upstream of the flashing.
- Step 2
Check the Attic Side
With a flashlight, look at the framing where the roof meets the wall. Staining that runs down the wall studs from above points to the wall; staining that starts on the roof deck points to the roof.
- Step 3
Note the Weather
Write down whether the leak followed rain blowing against that wall, a long steady rain, or a thaw. Different causes leak in different weather.
- Step 4
Get Both Trades Thinking
If the evidence points up the wall, a siding or window contractor may be the right first call. A good roofer will tell you when the roof is not the problem.
Signs Your Sidewall or Dormer Flashing Is Leaking
- A ceiling stain along the line where a lower roof meets a taller wall, often near the low end.
- Peeling paint, soft drywall or swollen trim on the wall directly below the bottom of a roof-to-wall joint, the spot a kickout should protect.
- Rot or stains on the exterior wall sheathing or siding just below the eave end of the joint.
- Dormer leaks that show up at the inside corners of the dormer window or on the dormer ceiling.
- Shingles cut back so far from the wall that you can see bare metal, or no metal visible at all, from a window or the ground with binoculars.
- Caulk lines along the top of the flashing or the bottom of the siding, a sign someone already chased this leak.
What a Proper Sidewall or Dormer Flashing Repair Involves
Fixing this joint right means getting to the metal. The bottom of the siding along the wall has to be released, and on vinyl and many sided walls it can usually be lifted and reset. Brick needs a fresh joint cut for counterflashing. The shingles along the wall come up so the old step flashing can be pulled and the deck checked for rot.
Then the joint is rebuilt in order: leak barrier membrane up the wall and onto the deck, new step flashing woven one piece per course, a kickout at the bottom, the wall's housewrap lapped back over the metal, and the siding reset with clearance above the shingles. Sealant only goes where the detail calls for it, not as the waterproofing.
Damaged siding, rotted wall sheathing, window flashing and interior drywall belong to other trades. A roofer repairs the roof side of the joint and should tell you plainly when the wall needs its own contractor.
Stellar Roofing Company prices a section of step flashing as a minor repair, $500 to about $1,500, when there is no wood damage. Longer walls, both sides of a dormer, masonry counterflashing or rotted decking move the work up a tier.
Two Licensed Trades Meet at This Joint in Michigan
Michigan's licensing law draws the same line this joint does. Under MCL 339.2404(3), a residential maintenance and alteration contractor license covers listed crafts and trades, and roofing is one trade while "siding and gutters" is a separate one. The statute says the license shall specify the particular craft or trade for which the licensee is qualified. A specialty contractor may take on work in another trade only when that work is incidental and supplemental to the licensed trade.
In practice, lifting and resetting a course or two of siding to replace step flashing is the kind of work a roofer does as part of a flashing repair. Re-siding a wall, rebuilding rotted wall sheathing or reflashing windows is siding and carpentry work in its own right. A residential builder license, which MCL 339.2401(a) defines around contracting to build, repair or alter a residential structure, is broader than a single trade. Before you hire anyone for the wall side, look up the license on LARA's lookup and check which license type, and for an M&A contractor which trade, it shows.
The licensing law also gives you a lever if this joint was built wrong recently. MCL 339.2411(2)(m) lists workmanship not meeting the standards of the Michigan Residential Code as a ground for discipline, and the code sections above require both step flashing and a kickout. Subsection (1) says a complaint about a maintenance and alteration contract must be made within 18 months after the latest of completion, occupancy or purchase. If a roof or siding job less than a year and a half old left this joint without a kickout or with reused step flashing, raise it with the contractor in writing first, and know that the LARA window is short.
Verifying a Michigan roofing license
How to run the LARA lookup and read license types and trades.
License lookupTime limits for workmanship claims
The 18-month LARA window alongside Michigan's contract and repose deadlines.
Michigan deadlinesWhat to Do if You Suspect This Joint
Photograph the stain and the outside of the wall above it. Note which way the wind was blowing during the rain that caused it. Do not climb onto the roof to caulk the joint: the caulk hides the evidence and rarely holds through a Michigan winter.
A free inspection, or a few clear photos sent to an inspector, will usually tell you whether you are dealing with roof flashing, a wall leak, or both. If the joint has been leaking for a while, ask for the deck and the wall sheathing at the bottom of the joint to be checked, because that is where long-running sidewall leaks do their damage.
Flashing problems explained
Our overview of where flashing fails across the roof, from chimneys to valleys.
Flashing issuesRotted roof deck
What happens to the plywood or OSB under a joint that has leaked for years.
Roof deck rotRoof Leak or Wall Leak at the Joint?
| Clue | Points to roof flashing | Points to the wall above |
|---|---|---|
| Where the water shows | Ceiling or attic side of the joint, roof deck stained | Inside the wall, around a window below, wall studs stained from above |
| When it leaks | Heavy rain on the roof, snowmelt, ice at the eave | Rain blowing against that face of the house |
| What you see outside | Bent, short or missing step flashing, no kickout, caulked joint | Open trim joints, cracked siding, unflashed window or vent above the roof |
| Who fixes it | Roofer | Siding or window contractor, sometimes with the roofer |
Many joints have both problems. The clues narrow it down; an inspection confirms it.
Leak Where the Roof Meets a Wall?
We will look at the flashing, the siding above it and the attic side of the joint, and tell you which one is letting water in. The inspection is free.
Related Guides
Why Roof Leaks Show Up Far From the Source
How water travels along the deck and framing before it drips.
Learn MoreRoof Leaks Only in Heavy Rain or Wind
Why some storms find a leak and others do not.
Learn MoreChimney Leak or Roof Leak?
Counterflashing, crowns and mortar: telling a masonry leak from a roof leak.
Learn MoreFlashing Repair
Wall, dormer, chimney and valley flashing rebuilt with new metal.
Learn MoreQuestions We Hear
What is kickout flashing and do I need it?
Kickout flashing is a small bent piece of metal at the bottom of a roof-to-wall joint that turns water away from the wall and into the gutter. The 2015 Michigan Residential Code requires a flashing that diverts water where a sloped roof's eave meets a sidewall, so a wall that runs past the end of a roof edge should have one. Without it, water from the whole wall pours into the eave corner and can rot the wall below.
Can step flashing be reused when a roof is replaced?
It can be done, but it is a common cause of leaks. Old pieces are often bent, nail-holed or sized for a different shingle exposure, and reusing them usually means not lifting the siding to set new metal properly. The code requires flashings that are rusted, damaged or deteriorated to be replaced on a reroof. New step flashing costs little compared with a repeat leak.
Why does my dormer only leak at the corners?
The front corners of a dormer are where the headwall flashing across the front meets the step flashing up each side. Those pieces have to be folded or overlapped into a corner that sheds water, and they often are not. A small gap, a cut that is too short or a bead of caulk standing in for metal will let water in during heavy or wind-driven rain, right at the corner of the dormer window or ceiling.
Is a leak at the bottom of a second-story wall a roof problem or a siding problem?
It can be either. If the stain is on the ceiling or the roof deck, look at the roof flashing first. If it is inside the wall, around a window below, or on wall framing stained from above, the water may be getting behind the siding higher up. A missing kickout can cause wall rot right at the bottom of the joint. An inspection that looks at both the roof and the wall above it is the fastest way to know.
How high above the roof should siding be?
GAF's shingle installation instructions call for siding to sit at least 2 inches above the roof surface while still covering the flashing by at least 2 inches. Siding that rests on the shingles can wick water, trap leaves and needles, and hold moisture against the roof and the bottom of the wall. Other shingle and siding manufacturers publish their own clearances, so check the product instructions for your house.
What This Page Cites
- 2015 Michigan Residential Code, Chapter 9 Roof Assemblies, Sections R903.2.1, R905.2.8.3, R905.2.8.4 and R908.5, UpCodes (https://up.codes/viewer/michigan/mi-residential-code-2015/chapter/9/roof-assemblies), accessed October 2026
- 2015 Michigan Residential Code, Chapter 7 Wall Covering, Sections R703.1, R703.2 and R703.4, UpCodes (https://up.codes/viewer/michigan/mi-residential-code-2015/chapter/7/wall-covering), accessed October 2026
- Timberline HDZ, UHDZ, AS II, CS, HDZ RS and RS+ Installation Instructions (RESTL622, 2023), GAF (https://images.thdstatic.com/catalog/pdfImages/ce/ce744b21-6c3d-4c1e-9396-919c6ffa7fe8.pdf), accessed October 2026
- MCL 339.2404, Residential builder and maintenance and alteration contractor licenses (crafts and trades, subsection (3)), Michigan Legislature (https://www.legislature.mi.gov/Laws/MCL?objectName=mcl-339-2404), accessed October 2026
- MCL 339.2401, Definitions (residential builder; residential maintenance and alteration contractor), Michigan Legislature (https://www.legislature.mi.gov/Laws/MCL?objectName=mcl-339-2401), accessed October 2026
- MCL 339.2411, Complaint period and grounds for discipline, Michigan Legislature (https://www.legislature.mi.gov/Laws/MCL?objectName=mcl-339-2411), accessed October 2026