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Installing Valleys and Flashing for Roofing Services: A Comprehensive Guide

installing valleys and flashing on a roof in cardiff

Roofing is one of the most crucial aspects of building construction, offering protection against the elements and contributing to the overall aesthetic appeal of a home. Among the various components of a roofing system, valleys and flashing play vital roles in ensuring the roof’s durability and functionality. This guide will walk you through the essentials of installing valleys and flashing, ensuring your roofing project is both efficient and long-lasting.

What are Valleys and Flashing?

Valleys are the V-shaped metal channels that run up and down the ‘folds’ of a roof. They are designed to direct rainwater and debris off the roof, preventing water from pooling and causing damage.

Flashing is a material, usually made of metal, that is used to seal and protect joints in a building from water penetration. It is commonly installed in areas where the roof plane meets a vertical surface, such as around chimneys, vent pipes, and roof valleys.

Steps for Installing Valleys and Flashing

1. Preparation

Before starting, ensure you have all the necessary tools and materials:

  • Metal valley flashing
  • Roofing nails
  • Hammer
  • Roofing cement
  • Ladder
  • Safety gear (gloves, safety glasses, harness)
2. Remove Old Roofing Material

If you are replacing old valleys and flashing, carefully remove the existing shingles and underlayment around the valley area. Clear any debris to create a clean working surface.

3. Install Underlayment

Lay down a layer of roofing underlayment, extending it into the valley area. This acts as an additional barrier against water penetration.

4. Position the Valley Flashing

Cut the valley flashing to the appropriate length, ensuring it runs the entire length of the valley. Place the flashing in the valley, securing it with roofing nails every 12 inches along the edges. Be sure to overlap sections by at least 6 inches if more than one piece is needed.

5. Seal the Edges

Apply a layer of roofing cement along the edges of the valley flashing to seal any gaps and prevent water from seeping underneath.

6. Install Shingles

Begin laying shingles, starting from the bottom of the valley and working upwards. Trim the shingles to fit along the edges of the valley flashing, leaving a small gap (about 2 inches) to allow for proper water runoff. Secure the shingles with roofing nails, ensuring they are firmly in place.

7. Flashing Around Roof Penetrations

For areas where the roof meets vertical surfaces (e.g., chimneys, vent pipes), install step flashing. This involves placing a piece of flashing at each step of the shingle, ensuring that each piece overlaps the one below it, creating a continuous barrier against water penetration.

8. Final Inspection

After installation, conduct a thorough inspection to ensure all flashing is properly sealed and all shingles are securely fastened. Look for any gaps or areas where water could potentially seep through and apply additional roofing cement if necessary.

Benefits of Proper Valley and Flashing Installation

  • Leak Prevention: Correct installation of valleys and flashing significantly reduces the risk of roof leaks, protecting the structural integrity of your home.
  • Longevity: Properly installed flashing extends the lifespan of your roof by preventing water damage and decay.
  • Aesthetic Appeal: Well-installed valleys and flashing contribute to a clean, professional look, enhancing the overall curb appeal of your home.


Installing valleys and flashing is a critical part of any roofing project. While it may seem daunting, following the steps outlined in this guide can help you achieve a durable and effective roofing system. Whether you are a DIY enthusiast or a professional roofer, attention to detail in these areas will ensure your roof stands the test of time.

For professional roofing services or more detailed guidance, consider consulting with experienced roofing contractors who can provide the expertise and precision needed for high-quality roofing installations.