How to Repair Roof Flashing Against a Wall

Repairing roof flashing against a wall is a common roofing task that prevents leaks where the roof meets vertical surfaces. This article covers assessment, materials, step-by-step repair methods for step and counter flashing, common mistakes, and maintenance tips to keep flashing watertight. Follow safety guidance and local building codes when working at heights.

Item	Typical Time	Difficulty
Inspection	30–60 Minutes	Low
Minor Sealant Repair	1–2 Hours	Low
Replace Counter Flashing	2–6 Hours	Medium
Install New Step Flashing Section	3–8 Hours	Medium–High

Why Flashing Against A Wall Matters

Flashing Prevents Water Intrusion At Roof-Wall Joints, where roof planes intersect vertical surfaces like chimneys, dormers, and siding. Failure of flashing causes hidden leaks, drywall damage, mold, and structural rot. Proper flashing directs water onto the roof surface and away from vulnerable seams.

Types Of Wall Flashing And When To Use Them

Common wall flashing setups include continuous (apron) flashing, step flashing, and counter flashing. The choice depends on roof slope, cladding type, and whether the wall receives siding, brick, or stucco.

Step Flashing

Used Where Roof Meets Vertical Wall Over Multiple Shingle Courses. Step flashing consists of a series of L-shaped metal pieces flashed under shingles and against the wall to create overlapping waterproofing.

Counter Flashing

Counter Flashing Covers The Top Edge Of Base Flashing and is typically embedded into mortar joints for chimneys or fastened behind wall cladding for siding. It protects the upper edge of base flashing from direct exposure.

Continuous (Apron) Flashing

One Long Piece That Bridges The Joint, used where a single sheet can be secured against the wall and over the roof edge, often seen at plumbing vent bases or simple roof-wall intersections.

Tools And Materials Needed

Gather Materials Before Starting to avoid delays: galvanized or stainless steel flashing, step flashing pieces, lead-coated copper for premium installs, polymer roofing cement, exterior sealant (urethane or silicone as appropriate), roofing nails, tin snips, pry bar, hammer, roofing nails, caulk gun, ladder, safety harness, chalk line, and tin snips.

Inspection: How To Diagnose Flashing Problems

Start With A Thorough Visual And Interior Inspection. Look for rusted/flared flashing, gaps, pulled fasteners, loose or missing counter flashing, cracked sealant, and water stains inside ceilings or walls directly below the wall-roof junction.

On siding or stucco walls, check mortar joints and weep screed areas. For chimneys, inspect mortar for erosion where counter flashing is embedded.

Minor Repairs: Resealing And Patching

Reseal Small Gaps And Replace Cracked Sealant where flashing meets wall or chimney. Remove loose or deteriorated caulk and apply a compatible exterior-grade sealant. Use roofing cement for small holes and metal-compatible sealants for long-term flexibility.

• Clean The Area removing dirt, rust, and old sealant before applying new products.
• Use Backer Rods for large gaps to allow proper sealant thickness and movement handling.
• Apply Sealant Smoothly and tool the bead to ensure adhesion and a continuous barrier.

Replacing Step Flashing: Step-By-Step

Replacement May Be Necessary When Flashing Is Corroded Or Missing. Work from the top down and replace shingles as needed to access each step flashing piece.

1. Remove A Few Shingles above the damaged flashing by lifting tabs and prying nails carefully.
2. Extract Old Flashing Pieces using a pry bar, taking care not to damage adjacent roofing felt or sheathing.
3. Install New Step Flashing Pieces one at a time: slide the vertical leg against the wall, tuck the horizontal leg under the shingle above, and nail through the top flange into the roof deck, not through the vertical wall leg.
4. Lap Each Piece Properly—each flashing should overlap the one below by at least 2 inches to ensure water sheds outward.
5. Reinstall Shingles and seal nail heads where necessary with roofing sealant.

Working With Counter Flashing And Masonry

Counter Flashing Embedded In Mortar Joints Requires Care. For chimneys, remove mortar where the counter flashing sits and cut the flashing to fit into a chase. Repoint mortar above flashing to secure it and create a tight joint.

When siding covers the top edge, tuck counter flashing behind siding or install a reglet (metal channel) into the wall to receive flashing. Never rely solely on caulk at the top of counter flashing; it’s a secondary barrier.

Best Materials And Corrosion Considerations

Choose Durable Metals For Longevity. Galvanized steel is economical, but stainless steel or copper resists corrosion longer. Use lead-coated copper only where allowed by code and environmental considerations.

Match fastener material to flashing to avoid galvanic corrosion. Use stainless steel screws with stainless flashing and hot-dipped galvanized nails where appropriate.

Common Mistakes To Avoid

Avoid These Frequent Errors That Cause Flashing Failure.

• Over-Reliance On Sealant Instead Of Proper Mechanical Flashing Overlaps.
• Improper Fastening: Nailing Through The Vertical Wall Leg, Creating Penetrations At Vulnerable Points.
• Insufficient Overlap: Flashing Should Overlap By At Least 2 Inches Per Course.
• Wrong Metals Together: Mixing Incompatible Metals That Promote Galvanic Corrosion.

When To Call A Professional

Hire A Licensed Roofer Or Mason For Complex Jobs such as counter flashing embedded into masonry, extensive roof and shingle replacement, or when the roof pitch and safety concerns exceed homeowner capability. Professionals can also ensure compliance with local building codes.

Safety And Building Code Considerations

Prioritize Fall Protection And Local Code Compliance. Use a safety harness, roof anchors, and stable ladders. Many jurisdictions require specific flashing details—check local building department guidance or permits before major work.

Maintenance Schedule And Long-Term Care

Regular Inspections Twice A Year And After Major Storms catch small problems before they become major leaks. Keep nearby gutters clean, trim overhanging branches, and monitor sealant condition. Replace flashing showing >30% corrosion or physical damage.

Cost Estimates And Factors Affecting Price

Repair Costs Vary By Scope, Material, And Access Difficulty. Simple resealing can cost under $200 in DIY materials, while professional replacement of flashing and shingles can run several hundred to a few thousand dollars depending on roof complexity and materials like copper.

Practical Example: Repairing Flashing At A Vinyl-Sided Wall

Step Flashing Under Vinyl Siding Requires A Reglet Or Tucking Technique. Remove a few courses of siding, slide vertical flashing behind the siding starter track, fasten and caulk the top edge, and reinstall siding. This maintains weathertightness without removing large siding sections.

Troubleshooting Persistent Leaks

If Leaks Continue After Flashing Work, Consider These Possibilities:

• Water Following A Path Behind Cladding Into The Wall Cavity
• Hidden Rot Or Damaged Sheathing Allowing Bypass Of Flashing
• Improperly Installed Underlayment Or Ice-And-Water Shield Missing At Eaves

Use water testing (garden hose) to isolate the leak area and inspect from attic or interior walls to track the water path.

Additional Resources And References

Consult Manufacturer Guides, Local Codes, And Trusted Roofing Associations such as the National Roofing Contractors Association (NRCA) for technical details and best practices. Manufacturer instructions for sealants and flashing materials provide compatibility and warranty information.

For complex masonry flashings, consult masonry restoration specialists or chimney services to ensure proper embedment and repointing methods.

Key Takeaways For Successful Roof Flashing Repairs

Effective Flashing Repairs Combine Proper Materials, Correct Installation, And Regular Maintenance. Ensure overlaps, secure attachment, compatible metals, and minimal reliance on sealant as a primary barrier. When in doubt or when work requires working with masonry or high roofs, hire a licensed professional.