Flashing where a metal roof meets a wall is a critical detail that prevents leaks and wind-driven moisture. The flashing must accommodate movement between roof and wall, channel water away, and resist local weather conditions. In the United States, walls range from brick and stucco to siding and concrete, each needing specific flashing strategies. This guide outlines common methods, materials, and installation steps to help builders, remodelers, and homeowners achieve lasting, watertight connections.
What Is Flashing At A Metal Roof Wall Intersection
Flashing at a roof-to-wall intersection forms a barrier against water intrusion and wind-driven rain. The flashing must accommodate movement between the wall and roof and be compatible with the selected metal roofing material to prevent galvanic corrosion. Proper flashing directs water down and away from the seam, protecting the interior structure and insulation.
Common configurations vary by wall type and roof style. On lower-pitched roofs with siding, step flashing is typical; on brick or stucco, a continuous wall flashing with counter flashing is used; on parapet walls, reglet systems and counter flashing are common. Choosing the right flashing depends on wall material, roof pitch, and climate conditions.
Key Flashing Methods For Metal Roofs Against Walls
Step Flashing For Wall Intersections
Step flashing consists of individual metal flashing pieces that alternate with roofing panels. Each piece is lapped over the wall, with the next piece stepping up the wall and under the next roof panel. This method creates a series of interlocking channels that shed water efficiently. Step flashing works well with wood, siding, and some masonry walls when paired with appropriate sealants and counter flashing.
Counter Flashing And Reglet Systems
Counter flashing is installed over base flashing to seal the joint where the wall meets the roof. A reglet—a groove or recessed channel in the wall or a mortar bed—accepts the counter flashing and provides a secure anchor. This approach is common on brick, stone, or stucco walls and on parapet walls. Proper installation prevents capillary action and ensures a continuous water barrier along the wall surface.
End Dams, Kick-Out Flashing, And Drains
End dams close the end of a flashing run to stop water from seeping behind panels. Kick-out flashing directs water away from the wall where it meets a vertical surface or gutter line. These details prevent moisture from migrating into the eave or interior wall cavity, especially on larger roof spans or where parapets meet roof planes.
For flat or low-slope sections, integrating drainage paths and ensuring clean runoff paths are essential. Use compatible sealants and flashing materials to maintain a continuous, watertight seam across transitions.
Materials And Tools
- Metal flashing: aluminum, galvanized steel, stainless steel, or copper, chosen for compatibility with the roof material.
- Counter flashing material: same metal as base flashing or compatible alloy.
- Backer rod and sealants: polyurethane or silicone-based sealants designed for exterior use and solar exposure.
- Butyl tape or other weatherproof tapes for underlayment redundancy.
- Reglet systems, fasteners, and closure strips as required by wall type.
- Underlayment or continuous membrane where required by code or climate.
- Tools: snips or shears, measuring tape, chalk line, hammer or driver, roofing nails or screws with appropriate washers, Caulking guns, and a pry bar.
Installation Guide: How To Flash A Metal Roof Against A Wall
- Assess the wall and roof intersection. Check for structural damage, moisture intrusion, and compatibility with the chosen flashing. Repair any wall substrates and clean the surface to ensure a solid bond.
- Prepare a clean, dry joining surface. Install an appropriate underlayment or membrane along the wall to bridge gaps and provide a smooth substrate for flashing. Maintain proper slope to ensure drainage away from the wall.
- Cut flashing pieces to fit. For step flashing, prepare several short pieces that can be overlaid with each roof panel as you work upward along the wall. Ensure each piece overlaps the previous by at least 2 to 4 inches, depending on weather exposure.
- Install base flashing along the wall. Start at the lowest point and progressively work upward. Secure with corrosion-resistant fasteners, placing fasteners where panels or wall materials provide solid backing. Leave a small gap for expansion if required by local code.
- Install counter flashing. Fit counter flashing over the base flashing and into the wall, sealing joints with a compatible sealant. For reglet systems, insert counter flashing into the reglet and seal at the joint with appropriate sealant to prevent water entry.
- Seal joints and transitions. Apply a continuous bead of exterior-grade sealant along all joints, ensuring it seals against both the metal and wall materials. Use a compatible sealant to resist UV exposure and temperature cycling.
- Install the metal roof panels. Align panels with the flashing and ensure proper overlap so water runs over the flashing rather than behind it. Secure panels with approved fasteners and maintain secure but flexible joints at the wall interface.
- Perform a water test. After installation, simulate rain with a garden hose at the wall intersection to verify a watertight seal. Look for leaks around fasteners, joints, and the edge where flashing meets wall material.
Common Mistakes And How To Avoid Them
- Inadequate overlap or improper lap direction. Ensure step flashing overlaps and that counter flashing covers the base flashing completely to prevent water intrusion.
- Using incompatible materials. Match flashing material to the roof metal to avoid galvanic corrosion; use compatible sealants and fasteners rated for exterior use.
- Skipping counter flashing on wall penetrations. Counter flashing is essential to seal joints and prevent moisture from migrating behind the flashing plane.
- Improper sealant selection. Use high-quality polyurethane or silicone sealants rated for exterior use and resist UV and temperature changes; avoid cheap silicone that can shrink over time.
- Ignoring wall type specifics. Brick, stucco, siding, and concrete each require different flashing details and attachment methods for a durable seal.
Maintenance And Inspection
- Schedule regular inspections after heavy rains, windstorms, or freeze-thaw cycles. Look for loose flashing, damaged seals, or corrosion.
- Check seals and joints annually and reapply sealant as needed. Use sealants designed for metal-to-wall joints to maintain flexibility and adhesion.
- Inspect for corrosion, especially on cheaper metals or in coastal environments. Replace damaged flashing promptly to prevent leaks.
- Ensure gutters and downspouts do not back up water toward the flashing. Keep drainage paths clear to maintain proper water shedding behavior.
- Document changes in climate or building envelope. If local codes change or the wall material is altered, reassess the flashing details to maintain a watertight connection.