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How to Seal Roof Valleys?

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How to Seal Roof Valleys?

Most roofing contractors agree that roof valleys are one of the most common places where leaks can occur on your roof. They are often susceptible to the effects of wind, rain, and snow which can all lead to leaky roofs.

What is a roof valley?

A roof valley is a small depression in the middle of a roof that allows water to run off the roof. It’s usually caused by an accumulation of ice or snow on top of the shingles. When it melts, this water runs down into the roof valley, making its way to the eaves where it can drip through the soffit onto the wall below causing a roof leak.

How To Fix A Roof Valley Leak

  1. Remove any loose debris from around the leaky area. This could include leaves, twigs, or even pieces of insulation. If you see any nails sticking up out of the roof decking, remove them as well.
  2. Check for damaged shingles or missing shingles near the leak. If there are any missing shingles, repair them before continuing with the rest of the project.
  3. Clean the area thoroughly using a soft brush and soap or detergent. Make sure to scrub the entire area including the edges of the roof decking.
  4. Use a waterproof membrane such as EPDM to cover the roof decking. You may need to use two layers depending on the size of the leak.
  5. Apply a layer of roof cement over the waterproof membrane. The roofing cement will help prevent moisture from getting under the membrane.
  6. Install flashing along the edge of the roof decking to divert water away from the roof. Flashing should be installed at least 12 inches above the highest point on the roof.
  7. Seal the roof decking with an asphalt-based roof coating.
  8. Cover the roof with tar paper. Tar paper acts as a barrier between the roof decking and the weather.
  9. Apply new shingles to the roof.
  10. Waterproof the roof decking again.

If fixing roofs is not your thing, we recommend that you get in touch with an experienced roofing professional.

Types of Roof Valley Systems

There are two types of roof valley systems:

Open valley roof

An open valley system has no covering material placed on top of the roof decking; instead, the roof decking is exposed to the elements. Open valley roofs are typically used when the roof is not expected to get very wet.

Closed valley roof

A closed valley system has some type of covering material placed on top of the roof decking. Closed valley roofs are typically used if the roof is expected to get wet. They are quite popular among homeowners. However, they do not last as long as the open valley roof.

Reasons for Roof Valley Leak

There are many reasons why roof valleys leak. Roof slopes, roofing material, roof shingles are some of the parts that contribute to leaks. Some of the other reasons include:

  • Poorly designed roof vents
  • Ice dams
  • Rust
  • Wind-driven rain
  • Snowmelt
  • Rainwater runoff
  • High humidity levels
  • Moisture condensation
  • Excessive heat
  • Low air pressure
  • Vibrations due to construction activity
  • Heavy rainfall

How to Prevent Roof Valley Leaks?

Preventing roof valley leaks is easy if you follow some basic guidelines. First, make sure that your roof has good ventilation. Your roof should have at least 1/16th inch per foot of open space between the shingles. Second, keep your gutters clean. Third, inspect your roof every year. Look for signs of damage like holes or missing shingles.

The best way to prevent roof valley leakage is to keep your roof dry. That means keeping it free of leaves, sticks, and other debris. Also, make sure that the gutters are clear of obstructions.


Should roof valleys be sealed?

Yes, they should be sealed. However, you don’t necessarily need to do it yourself. There are plenty of companies that specialize in sealing roof valleys.

Can I seal my own roof?

If you know what you’re doing, then yes, you can. But we recommend hiring someone else to do the job instead.

What kind of materials should I use to seal my roof?

You can use either a silicone-based product or a latex-based product.

Is it necessary to install flashing when sealing roof valleys?

It depends on where the leak occurs. Installing flashing is not required in all cases. However, it’s highly recommended if the leak happens near the eaves or ridgeline.

Check our previous post here: What Is GRP Roofing (UK)?