Roof Valleys: Why They Leak and How to Flash Them Correctly

Water stain in your ceiling. Always in the same spot. Always after heavy rain.

We climb into your attic. Trace the water path. It's coming from the valley.

Valley leaks are the second most common roof leak we see in Richmond (chimneys are first). Here's why they fail and how to fix them permanently.

What Roof Valleys Are

A valley is where two roof slopes meet at an inside corner, forming a V-shape.

Purpose: channels water from both slopes down toward the gutter.

Problem: water volume. A valley handles water from two roof planes. Heavy rain means high-velocity water flow concentrated in a narrow channel.

That stress means valleys fail more often than the rest of your roof.

Types of Valley Construction

There are three main methods. Each has pros and cons.

1. Open Metal Valley

Construction:

• Metal flashing (aluminum, steel, or copper) runs the length of the valley
• Shingles are cut back about 2 inches on each side
• Valley channel is exposed (you can see the metal)

Pros:

• Channels water efficiently (metal is slick, water flows fast)
• Easy to inspect (you can see if there's debris buildup)
• Lasts as long as the metal (30-50 years for aluminum, 100+ for copper)
• Less prone to leaks

Cons:

• Visible metal (some people dislike the look)
• Costs more (metal material + labor to cut shingles precisely)

Our take: This is the best method. More durable, fewer leaks, worth the extra cost.

Cost: Add $200-400 to a typical roof replacement.

2. Closed Cut Valley (California Valley)

Construction:

• Shingles from one slope run across the valley
• Shingles from the other slope are cut to overlap the valley center
• No exposed metal (valley is covered with shingles)

Pros:

• Uniform appearance (no visible metal)
• Slightly cheaper than open valley
• Acceptable in most situations

Cons:

• Water flows over shingles, not metal (slower drainage)
• Cut edges of shingles are vulnerable to wind lift
• Harder to clean debris from the valley
• Leaks more common than open valley

Our take: Fine for moderate climates. In Richmond's heavy rain, we prefer open valleys.

Cost: Standard on most roof replacements (no additional charge).

3. Woven Valley

Construction:

• Shingles from both slopes weave together in the valley
• No exposed metal, no cut edges
• Each course alternates which side goes on top

Pros:

• Looks uniform (no visible seam)
• Traditional method (common on older roofs)

Cons:

• Time-consuming to install (most roofers avoid it)
• Difficult to replace individual shingles later
• Debris accumulates easily
• Not recommended by most shingle manufacturers anymore

Our take: We don't install woven valleys. They're outdated and leak-prone.

Cost: N/A (we don't offer this method).

Why Valleys Leak

1. Inadequate or Missing Ice and Water Shield

Valleys should have ice and water shield (a self-sealing underlayment) running their entire length. Minimum 36 inches wide (18 inches on each side of the valley center).

Some contractors skip it or use standard felt underlayment instead.

When water backs up (heavy rain, ice dams), felt lets it through. Ice and water shield doesn't.

We've fixed dozens of valley leaks simply by removing the shingles and adding proper ice and water shield.

2. Valley Metal Too Narrow

Open valleys should use metal flashing at least 24 inches wide (12 inches on each side of center).

We've seen 12-inch and 18-inch valley metal. Not wide enough. Water volume during heavy rain exceeds the channel width. Water flows under the shingles.

Proper width: 24 inches minimum. 36 inches for long valleys or steep pitches.

3. Poor Shingle Overlap

In closed cut valleys, shingles need to overlap the valley center by at least 12 inches.

Contractors in a hurry sometimes cut shingles too close to the valley line. Water flows across the exposed edge and leaks through.

4. Valley Debris Accumulation

Leaves, pine needles, shingle granules — they all wash down and collect in valleys.

Over time, debris dams the valley. Water backs up under shingles.

Valleys need cleaning more often than the rest of your roof. Twice a year minimum if you have trees.

5. Improper Valley Flashing Crimps

Open valleys need a center crimp (a small raised ridge down the middle). This prevents water from one slope jumping across to the other slope's shingles.

Flat valley metal lets water spread. Crimped metal directs it downward.

Some contractors don't crimp the metal. Water washes sideways, under shingles, into your attic.

6. Valley Meets Gutter at Wrong Angle

Valleys that dump directly into a gutter sometimes create problems.

High-velocity water from the valley overshoots the gutter, especially if the roof pitch is steep.

We've seen valleys that send water straight past the gutter and down the fascia. Looks like a leak. Actually a design problem.

Fix: add a splash guard or redesign the gutter position.

How to Flash a Valley Correctly

Here's our process for open metal valleys (the method we use on every complex roof):

Step 1: Install Ice and Water Shield

Run ice and water shield the full length of the valley, minimum 36 inches wide. Overlap seams by 6 inches. Press firmly to ensure adhesion.

Step 2: Install Valley Metal

Use pre-formed valley metal (24-30 inches wide) with a center crimp. Overlap sections by 12 inches, sealed with roofing adhesive. Secure with roofing nails every 8-10 inches along the outer edges (never in the valley center).

Step 3: Install Shingles

Cut shingles to leave 2-3 inches of exposed metal on each side of valley center. Angle cuts to match the valley line. Seal cut edges with roofing adhesive to prevent wind lift.

Step 4: Quality Check

Inspect valley for:

• Continuous ice and water shield (no gaps)
• Properly crimped metal
• Correct shingle cutback distance
• Smooth metal (no dents or wrinkles)
• Adequate fastening (no loose sections)

Done correctly, this valley won't leak for 30+ years.

Open Valley vs. Closed Valley: Which to Choose?

Choose open metal valley if:

• Your roof has long valleys (over 15 feet)
• You live in an area with heavy rainfall (Richmond qualifies)
• You have steep roof pitches (water flows fast)
• You want maximum durability
• You have lots of trees (easier to clean debris)

Closed cut valley is acceptable if:

• Valleys are short (under 10 feet)
• Roof pitch is moderate (4:12 to 6:12)
• You prioritize appearance over slight performance difference
• Budget is tight (saves $200-400)

Our default: Open metal valleys on every roof. The durability and leak resistance are worth the minimal extra cost.

Valley Metal Materials

Aluminum:

• Most common
• Affordable ($3-5 per linear foot)
• Won't rust
• Lasts 30-40 years
• Available in white, brown, or mill finish

Galvanized Steel:

• Stronger than aluminum
• Slightly cheaper ($2-4 per linear foot)
• Can rust over time (usually 20-30 years)
• Heavier (better wind resistance)

Copper:

• Premium option
• Very expensive ($15-25 per linear foot)
• Lasts 100+ years
• Develops green patina over time
• Used on high-end and historic homes

Our choice: Aluminum for most Richmond homes. Copper for historic properties in The Fan or high-end projects.

Richmond-Specific Valley Challenges

Heavy summer thunderstorms. June through August, we get downpours that dump 2-3 inches in an hour. Valleys handle enormous water volume during these events.

Ice dams. Valleys are prime locations for ice dam formation. They're low points where snow collects and melts.

Debris from oak trees. Leaves and acorns funnel into valleys. Requires regular cleaning.

Complex roof designs. Many Richmond colonials and victorians have multiple valleys (4-6 per roof). Each is a potential leak point.

Maintaining Your Valleys

Twice-yearly inspection:

• Spring (after pollen season)
• Fall (after leaves drop)

What to check:

• Debris accumulation (clean it out)
• Shingle edges (look for lifting or curling)
• Exposed metal (check for rust or damage)
• Water stains in attic below the valley

Cleaning process:

1. Carefully climb onto roof (safety first)
2. Use leaf blower or soft brush to remove debris
3. Flush with garden hose (never pressure washer)
4. Inspect for damage while you're there

Professional cleaning: $150-250 if you're not comfortable on the roof.

Signs of Valley Problems

Inside:

• Water stains on ceiling along the valley line
• Drips during or shortly after heavy rain
• Musty smell (mold from persistent moisture)

Outside:

• Shingles curling or lifting near valley
• Visible gaps between shingles and valley metal
• Rust stains on valley metal
• Debris buildup that doesn't clear with rain

In attic:

• Water stains on decking along valley
• Wet insulation
• Daylight visible through valley area

Any of these? Call for an inspection.

Valley Replacement Cost

Open metal valley installation (new roof):

• Material: $3-5 per linear foot (aluminum)
• Labor: $8-12 per linear foot
• Total: $11-17 per linear foot
• Typical valley (15 feet): $165-255

Valley repair (existing roof):

• Remove shingles along valley (4-6 feet on each side)
• Replace ice and water shield
• Install new valley metal
• Reinstall shingles
• Cost: $400-700 per valley

Full valley replacement on existing roof:

• Similar to repair but full length of valley
• $600-1,200 per valley depending on length

Expensive compared to patching. But valley leaks don't get better on their own. Temporary fixes (caulk, tar) last maybe 6 months.

Questions to Ask Your Roofer

"Do you install open or closed valleys?" Open is better. If they only do closed, ask why.

"What width valley metal do you use?" Should be minimum 24 inches.

"Do you install ice and water shield under the valley?" Only acceptable answer: yes, full length, 36 inches wide minimum.

"Do you crimp the valley metal?" Should say yes (for open valleys).

"Can I see photos of your valley work?" They should have plenty. Look for clean, straight valleys with proper shingle cutback.

What We Install

Open metal valleys with:

• 36-inch wide ice and water shield (full length)
• 24-inch pre-formed aluminum valley metal (or copper on high-end projects)
• Center crimp for water control
• 2-3 inch shingle cutback on each side
• Sealed cut edges to prevent wind lift

We install the same valley method on a $9,000 ranch roof as on a $35,000 colonial. No shortcuts based on budget.

Want to see examples? We've got photos from 50+ Richmond valley installations in the past two years.

Call (804) 238-7837 or request an inspection if you suspect valley leaks or want an honest assessment of your valley condition.

Final Thoughts on Valleys

Valleys are high-stress areas. Water volume, debris accumulation, ice dams — they handle it all.

Cheap out on valley construction and you'll pay for it later in leaks and repairs.

Spend the extra $200-400 for open metal valleys with proper ice and water shield. Your ceiling (and your wallet) will thank you.

And clean those valleys twice a year. Ten minutes with a leaf blower prevents thousands in future damage.