How to Fix a Dead Valley Where Water Dumps Into a Wall or Flat Spot
When a valley ends against a wall, a dormer or a flat roof, all its water arrives in one place. Split it, slow it or carry it past.
- Professional
- 4 to 8 hours
- Updated
The short answer
A dead valley is a valley that ends where it cannot drain cleanly, against a wall, at a dormer, or on a low or flat roof. All its water dumps at one point. Fix it by building a cricket or diverter to split the flow, running wider metal and two layers of ice and water shield up the wall, adding a kickout or end dam, and sending water out to a gutter or downpipe.
A valley is supposed to lead water down to the eave and into a gutter. A dead valley is one that cannot. It ends against a wall, at the side of a dormer, at a chimney or on a flat or very low pitched roof, and everything the valley collects from two planes arrives at that one spot in a rush. The water has nowhere to go, so it sheets across whatever is there and finds any weak point: a wall joint, a flashing seam or a low-slope roof that cannot shed it fast enough.
These are some of the most common leak locations on houses with additions and complex rooflines. The fix is not more sealant. It is to manage the water: split it, slow it, carry it to a gutter, and double up the waterproofing where it lands. See also how to handle valleys with unequal pitches and flashing a pitch change, which are frequent partners of dead valleys.
Tools
- Sheet metal brake
- Tin snips (straight cut and offset)
- Hand seamer
- Tape measure
- Roofing hammer
- Caulking gun
- Hook blade utility knife
- Cut resistant gloves
Materials
- Ice and water shield, 36 inch and 18 inch wide rolls
- W-valley metal, 24 inches or wider
- Sheet metal for a diverter, kickout or end dam
- Plywood and 2 by 4 lumber for a cricket if needed
- Roofing nails, 1-1/4 inch
- Polyurethane or hybrid polymer sealant for metal joints only
- Shingles or matching roofing
Safety first
- Dead valleys are usually at the junction of two roof planes and a wall, often high on the house. Work tied off. WorkSafeBC requires fall protection at 3 metres (about 10 feet) and wherever a fall could cause serious injury.
- Working against a wall with a steep valley at your back is a fall risk. Use a roof anchor above you and a lifeline with a rope grab, not just a guardrail in your mind.
- If the valley ends above a porch, walkway or entry, keep people clear during demolition and water testing.
Step by Step
Step 1: Find out where the water goes and how much arrives
Estimate the roof area feeding the valley. A 10 by 10 foot plane in heavy rain is one thing, two large planes from a two-storey gable is another. The larger the catchment, the more important it is to split the flow and carry it to a downpipe rather than onto a lower roof.
Note what the valley ends against: a sidewall, a headwall, a dormer, a chimney or a flat roof. Each needs its own end detail. See how to flash a headwall and how to flash a dormer.
Step 2: Strip back to the deck and inspect
A dead valley has usually been leaking for some time, and the deck and wall framing around it are the most likely to be wet or rotted. Probe with a screwdriver. Replace soft sheathing and treat any framing damage before building the new detail. See how to replace roof sheathing.
If the wall is cladded, lift the lowest courses to look at the building paper and sheathing behind.
Watch out: If framing is damaged, stop and have it assessed. New flashing over rotting framing hides the problem.
Step 3: Build a cricket or diverter to split the flow
A diverter is a small peaked sheet metal piece, like a mini roof, fitted at the end of the valley. It splits the flow into two streams and sends each along the wall or down the lower plane, so the water does not slam into the wall in a single jet. For larger flows, frame a full cricket in the same way as you would behind a chimney.
Cover a cricket with membrane and metal. The ridge of the diverter should point up the valley, and its sides should slope away to the lower roof or to a gutter.
Step 4: Lay doubled membrane and turn it up the wall
The first layer is the normal 36 inch valley strip. The second is a wider or second layer across the end, running up the wall at least 6 inches and lapping onto the lower roof by at least 12 inches. Make sure the wall's building paper laps over the membrane on the wall, not behind it.
Press the membrane into every corner, because a void under it at the corner is the first place a nail will tear it.
Step 5: Run wide valley metal to the end
Metal is the best material for a dead valley because it does not depend on shingles lapping. Set the metal over the membrane, extend it past the valley end onto the lower roof or gutter, and turn up an end dam at the wall so water cannot run behind it. Lap sections 6 to 8 inches, upper over lower. See how to install an open metal valley.
Fasten only along the outer edges. Never nail the channel.
Step 6: Add a kickout or extend the metal to a gutter
Where the valley water ends at the bottom of a wall, a kickout flashing turns it out into a gutter instead of behind the cladding. The gutter must have capacity for the load: a valley bringing two large planes into a standard gutter will overshoot it, so check for a larger downpipe or a downpipe right at the valley end.
If the valley ends on a lower roof, extend the metal a full 12 inches or more past the valley end and onto the shingles of that roof, sitting over them. It is better to run water visibly onto the lower roof than to hide it under shingles.
Step 7: Reshingle and seal the wall joint properly
Reshingle around the metal, trimming to the cutlines and keeping every nail out of the valley. Seal the metal joints and the end dam with a polyurethane or hybrid sealant, used only at joints and never as a substitute for lap. See how to choose and apply roofing sealants.
Close the wall with the building paper lapped over the membrane and the cladding clear of the roof, as in wall flashing by cladding type.
Step 8: Water test the detail
Have a helper in the attic. Start the water at the top of the valley, not at the detail, so you can see how the water flows and where it arrives. Watch the diverter, the end dam and the kickout.
If any water shows in the attic or at the wall, stop and find where it entered before leaving. A dead valley detail that passes a hose test has a much better chance of surviving a wet fall.
Common Dead Valley Situations
- Valley into a sidewall: water hits the wall at speed. Needs a diverter or kickout, and membrane turned up the wall.
- Valley into a dormer: the dormer's cheek wall takes the water. Wide metal, step flashing and a kickout are all needed.
- Valley onto a low or flat roof: the lower roof must be able to drain the load. Add a scupper or extend a gutter.
- Valley ending at a chimney: a cricket on the upslope side is the detail. See how to build a chimney cricket.
- Valley ending above an entry or deck: run the water to a downpipe so it does not fall on people or rot the structure below.
Why Sealant Is Not the Fix
Dead valleys are often caulked repeatedly by owners who find a leak at the wall. The sealant cracks, water gets behind it, and the leak gets worse. The fix is to change where the water goes, not to seal the point where it lands.
Common Mistakes
- Sealing instead of diverting. Caulk at the wall joint cracks within a season. The water volume is the problem.
- No kickout. Water running down the wall end soaks the wall cladding and sheathing.
- Shingles under the valley end. Water lapped under the shingles of a lower roof finds its way into the deck.
- A single thin membrane layer. This is the most heavily watered point on the roof and deserves two layers.
- No capacity in the gutter. A standard gutter and one downpipe cannot take two large planes at once.
- Metal too short. A valley that stops at the wall edge leaves water to run behind it.
When to Call a Professional
Dead valleys involve wall flashing, framing, metal work and drainage, and they often sit over finished living space. They are not a first project. A roofer will trace the water, check the framing, and build the diverter, metal and kickout as one detail.
If water is already staining a ceiling below the valley end, the sheathing or framing is likely wet, and it should be assessed before any roofing is repaired.
Fraser Roofing does free roof inspections across the Fraser Valley, from Hope to Abbotsford. See our Roof Repair service or the towns we cover.
How to Fix a Dead Valley: Questions
What is a dead valley on a roof?
A dead valley is a valley that ends at a wall, a dormer, a chimney or a flat roof instead of draining down to the eave. All the water from the valley arrives at that one point, where it can overshoot the flashing and run behind the wall. They need diverters, wider metal, extra membrane and a way to carry the water to a gutter.
Why does my valley leak where it meets the wall?
The water from two roof planes hits the wall at speed and can run up behind the flashing, wick under shingles or overflow the detail. Common causes are no diverter or kickout, single-layer membrane, short valley metal and old caulking. A fix manages the water with a cricket or diverter, wider metal and a kickout.
What is a kickout flashing for?
A kickout flashing turns water coming off the end of a roof to wall joint out into a gutter instead of letting it run down behind the wall cladding. On a dead valley it carries the concentrated valley flow past the wall. Without one, water soaks the sheathing below the roof line and rots the wall over time.
Can I fix a dead valley with roof cement?
Roof cement is at best a temporary patch. It cracks with sun and temperature changes, and a dead valley sends enough water to find any gap. A lasting fix changes how the water is handled: a diverter or cricket to split it, wide metal, doubled membrane turned up the wall and a kickout or gutter to carry it away.
Related Guides
All Roof Valleys 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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