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How to Properly Flash a Headwall

Date: November 26, 2023

Understanding Headwall Flashing: A Crucial Component for Water Management

Headwall flashing plays a critical role in roofing by facilitating the smooth transition of water from siding to the roof, redirecting it away from the wall. This essential process significantly safeguards the structural integrity of any building. Usually situated at the intersection of a roofline and a vertical wall, headwall flashing becomes a necessary fixture in various architectural designs. Its primary function is to prevent water from infiltrating the structure, averting potential damage and preserving the building's durability.

By efficiently managing water runoff, headwall flashing ensures that moisture doesn't compromise the wall or the roof's integrity. This small but pivotal component is instrumental in maintaining the overall health and longevity of the building. Its presence is particularly crucial in areas prone to heavy rainfall or adverse weather conditions, underscoring its significance in preserving the structure's soundness.


Components of Headwall Flashing

  1. Siding: Siding is the outer covering or cladding of a building's walls. It's both decorative and functional, protecting the interior walls from weather elements like rain, snow, and wind. It's available in various materials like vinyl, wood, fiber cement, brick, or metal. Properly installed siding helps direct water away from the structure, preventing moisture from seeping into the walls.
  1. House Wrap: This is a moisture and air barrier installed beneath the siding. It helps prevent water from penetrating the walls while allowing water vapor to escape, maintaining a dry and well-insulated interior. House wraps also contribute to energy efficiency by reducing air leakage.
  1. Counter-Flashing: Counter-flashing is installed over the primary flashing to provide an additional layer of protection against water infiltration. It's typically used in conjunction with primary flashing to seal and prevent water from getting behind the flashing, especially in areas prone to water accumulation.
  1. Flashing: This thin, waterproof material is used at critical points on a building, such as roof-to-wall intersections or around chimneys and skylights. It prevents water from penetrating vulnerable areas by directing it away from these junctions, ensuring that water doesn't infiltrate the building envelope.
  1. Underlayment: Underlayment is a layer of material installed beneath the roof-covering material (such as shingles, tiles, or metal) and on top of the roof sheathing. It acts as an additional barrier against moisture, providing extra protection to the roof structure from water infiltration.
  1. Roof Sheathing: This is the structural layer, typically made of plywood or oriented strand board (OSB), installed over the rafters or trusses. It provides a sturdy base for the roof covering material and supports the weight of the roofing materials and any external loads (like snow or wind).
  1. Roof-Covering Material: This is the outermost layer of the roof that directly faces the elements. It can include shingles, tiles, metal panels, or other materials. The roof covering material protects the roof sheathing and underlying structure from weather elements like rain, snow, UV rays, and wind.
Headwall installment

Installation Process and Importance

The installation of headwall flashing involves a meticulous process where each layer is strategically placed to ensure optimal water flow. 

Installation process:

  • Underlayment and Sheathing: These are the foundational layers of the roof. The sheathing provides structural support while the underlayment, typically a waterproof barrier like felt or synthetic materials, adds an extra layer of protection against water intrusion. They form the base upon which the roof-covering material will be laid.
  • Roof-Covering Material: This can vary depending on the type of roof being installed—shingles, tiles, metal sheets, etc. This material is installed over the underlayment and sheathing, forming the visible and protective outer layer of the roof.
  • Flashing: Flashing is a thin, weather-resistant material (often metal such as aluminum or galvanized steel) designed to divert water away from critical areas prone to leaks. In the case of headwall flashing, it's placed at the intersection of the roof and the wall. It prevents water from seeping into this vulnerable joint by directing it away from the seam.
  • Counter-Flashing: This is installed over the top of the flashing to provide an extra layer of protection and to secure the flashing in place. It helps to further direct water away from the joint and prevents it from getting behind the flashing.
  • House Wrap: This layer is part of the wall assembly. It's a moisture-resistant barrier that goes over the sheathing and under the siding. It acts as an additional defense against water infiltration, protecting the structural integrity of the wall system.
  • Siding: This is the visible exterior cladding of the building. It goes over the house wrap and provides aesthetic appeal while also offering some protection against the elements.

Importance of each layer:

  • Underlayment and Sheathing: They provide structural support and a barrier against water that might penetrate the roof covering.
  • Roof-Covering Material: Protects the underlayment and sheathing from direct exposure to the elements while enhancing the building's aesthetics.
  • Flashing and Counter-Flashing: Essential for preventing water intrusion at vulnerable joints like roof-wall intersections, safeguarding against leaks and potential damage.
  • House Wrap: Protects the wall assembly from moisture that might penetrate the siding, preventing issues like rot and mold.
  • Siding: Provides the final layer of defense against weather while enhancing the building's appearance.

The correct installation of headwall flashing is vital for several reasons:

  1. Prevents Water Damage: By effectively channeling water away from the wall and onto the roof, headwall flashing prevents water from penetrating the structure, thereby avoiding potential water damage.
  2. Enhances Roof Longevity: Properly installed flashing contributes to the longevity of the roof by preventing water accumulation and subsequent deterioration.
  3. Improves Energy Efficiency: By keeping moisture out, headwall flashing aids in maintaining the insulation properties of the walls, which can contribute to overall energy efficiency.


In summary, headwall flashing isn't merely a roofing necessity; it's pivotal for building durability. Its significance in water management cannot be emphasized enough. Correct installation is vital for structural health. A well-flashed headwall ensures a secure, dry, and enduring home. It's integral to the integrity and longevity of any structure. Efficient water flow management is its primary function, safeguarding against potential damage.

Neglecting proper installation compromises the building's health. Therefore, recognizing its critical role is paramount. The secure installation of headwall flashing secures the home against moisture infiltration, contributing significantly to its longevity. The importance of this component extends beyond mere necessity; it's a safeguard for the overall well-being of the structure. Always remember, investing in quality headwall flashing pays dividends in maintaining a sturdy, watertight home.

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