Why Valleys Are Critical

Valleys are where two roof planes meet at an inside angle. Water from both planes flows into the valley, concentrating 2-4x the water volume of flat sections. This makes valleys the second most common leak location (after chimneys).

Valley Failure Modes:

• Corroded flashing: Rust holes in galvanized steel
• Inadequate flashing width: Too narrow for water volume
• Improper shingle cuts: Water runs under shingles
• Debris accumulation: Leaves and needles block water flow
• Ice dam formation: Valleys are prone to ice dams in winter

Valley Types

Open Valley (Recommended):

• Metal flashing visible in valley center
• Shingles cut back from valley center
• Superior water shedding
• Easier to clean and maintain
• Longer lifespan
• This is our recommended method

Closed Valley (Woven or Cut):

• Shingles cover valley (no visible flashing)
• Relies on underlayment for waterproofing
• More prone to leaks
• Difficult to clean
• We do not recommend this method

Before You Start

Skill Level: Intermediate to Advanced

Time Required: 2-4 hours per valley

Cost: $50-150 per valley (DIY) vs. $200-400 (professional installation)

Required Tools

• Tin snips (for cutting flashing)
• Utility knife with hook blades
• Chalk line
• Tape measure
• Straight edge (4-6 feet)
• Hammer or roofing nailer
• Caulk gun

Materials Needed

• Valley flashing (24-36 inches wide, galvanized steel, aluminum, or copper)
• Ice & water shield (36 inches wide)
• Roofing nails
• Roofing cement
• Shingles (to match existing roof)

Step 1: Prepare Valley

Process:

1. Remove old valley material: If re-roofing, remove old flashing and shingles
2. Inspect deck: Check for rot or damage in valley area
3. Clean valley: Remove all debris, nails, and old sealant
4. Ensure proper slope: Valley should drain freely (no flat spots)

Step 2: Install Ice & Water Shield

Why This Matters:

Ice & water shield provides a waterproof backup layer. Valleys are prone to ice dams and wind-driven rain. This is your last line of defense.

Installation:

1. Center in valley: 36-inch wide ice & water shield, 18 inches on each side of valley center
2. Start at eave: Work upward toward ridge
3. Overlap upslope: 6 inches where pieces meet
4. Press firmly: Ensure complete adhesion to deck
5. Smooth out wrinkles: Wrinkles can cause water to pool

Step 3: Install Valley Flashing (Open Valley Method)

Flashing Material Selection:

• Galvanized Steel: Most common, affordable, 20-30 year lifespan
• Aluminum: Lightweight, won't rust, 30-40 year lifespan
• Copper: Premium, 50+ year lifespan, expensive

Flashing Width:

• Standard: 24 inches wide (12 inches each side of center)
• High-volume valleys: 36 inches wide (18 inches each side)
• Fraser Valley recommendation: 24 inches minimum, 36 inches for complex roofs

Installation:

1. Center flashing in valley: Equal width on each side of valley center
2. Start at eave: Extend 1-2 inches past drip edge
3. Nail edges only:
   • Nails 1 inch from edge
   • Spacing: 12 inches on center
   • DO NOT nail in valley center (allows thermal expansion)
4. Overlap upslope: 12 inches where flashing pieces meet
5. Seal laps: Apply roofing cement to overlap areas
6. Extend to ridge: Flashing should extend over ridge by 6 inches

Step 4: Install Shingles Along Valley

Critical Details:

Shingle placement determines water flow. Improper cuts allow water to run under shingles.

Process:

1. Install shingles on one side first: Work from eave to ridge
2. Extend shingles into valley: At least 12 inches past valley center
3. Nail shingles: Keep nails 6 inches from valley center (prevents water infiltration at nail holes)
4. Install shingles on opposite side: Overlap first side's shingles

Step 5: Cut Shingles for Open Valley

Chalk Line Layout:

1. Snap chalk lines:
   • 2-3 inches from valley center on each side
   • Lines should widen slightly toward eave (1/8 inch per foot)
   • This creates a slight "V" shape that improves water flow

Cutting Process:

1. Cut along chalk lines: Use utility knife with hook blade
2. Cut from top: Cleaner cut than cutting from bottom
3. Use straight edge: For clean, straight cuts
4. Clip corners: 45-degree cut at top corner of each shingle (directs water into valley)
5. Seal cut edges: Dab of roofing cement under each cut edge

Step 6: Final Sealing

Critical Final Steps:

1. Inspect all cuts: Ensure clean, straight cuts with no loose edges
2. Seal shingle edges: Apply roofing cement under cut edges
3. Check flashing laps: Verify 12-inch overlap and proper sealing
4. Clean valley: Remove all debris and excess sealant

Alternative: Closed Valley (Not Recommended)

Why We Don't Recommend It:

Closed valleys rely on underlayment for waterproofing. When underlayment fails (and it will), the valley leaks. Open valleys provide visible, durable metal flashing that lasts 30+ years.

If You Must Use Closed Valley:

1. Apply ice & water shield: 36 inches wide, centered in valley
2. Weave or cut shingles:
   • Woven: Shingles from each side interlace in valley
   • Cut: One side extends across valley, other side cut to overlap
3. Seal all cuts: Generously apply roofing cement

Fraser Valley Specific Considerations

Heavy Rain:

• Use 36-inch wide flashing for high-volume valleys
• Ensure valley has adequate slope (no flat spots)
• Clean valleys annually to prevent debris buildup

Ice Dams:

• Extend ice & water shield 36 inches on each side of valley center (72 inches total)
• Ensure proper attic insulation and ventilation
• Consider heat cables for problem valleys

Moss and Debris:

• Open valleys are easier to clean than closed valleys
• Install zinc strips at ridge to reduce moss growth
• Clean valleys twice per year (spring and fall)

Common Mistakes to Avoid

1. Nailing in Valley Center

Nails in the valley center create leak points. Nail edges only, 1 inch from edge.

2. Inadequate Flashing Width

Using 18-inch flashing instead of 24-36 inches. Narrow flashing can't handle water volume.

3. Not Clipping Shingle Corners

Failing to clip corners causes shingles to wick water under adjacent shingles.

4. Insufficient Ice & Water Shield

Using 18-inch ice & water shield instead of 36 inches. Valleys need extra protection.

5. Using Closed Valley Method

Closed valleys are prone to leaks. Open valleys are superior in every way.

Maintenance

Annual Valley Inspection:

• Clean debris (leaves, needles, granules)
• Check for rust or corrosion (galvanized steel)
• Inspect shingle cuts (ensure edges are sealed)
• Look for standing water (indicates poor slope or blockage)

When to Replace Valley Flashing:

• Rust holes visible
• Flashing is severely corroded
• Persistent leaks despite repairs
• Flashing is 25+ years old

The Bottom Line

Valley installation is straightforward but critical. Mistakes cause leaks that damage interior ceilings and walls. Open valley method is superior to closed valley in every way: better water shedding, easier maintenance, longer lifespan.

At RJ Roofing Bros, we install open valleys with 24-36 inch flashing and full ice & water shield coverage. We know the details that prevent leaks: proper flashing width, correct shingle cuts, and adequate sealing. We warranty our work.

Valley leaking? Call (604) 997-1292 for expert valley repair.