Corroded metal flashings on shingle roof

Causes

Acidic leachate from cedar or H4-treated timber shingles (containing copper-based preservatives)

Air-borne salt, dust or dirt accumulating on or under the flashing

Listed under: Property locations, Exterior, metal, copper, Roof, flashings, corrosion, rust, timber shingles and shakes

Cause

Acidic leachate from cedar or H4-treated timber shingles (containing copper-based preservatives)

Repair

  • closely examine the condition of the flashing. Where rusting is minor it should be removed with sanding. Paint with a zinc-rich primer and then at least two coats of acrylic paint. This may only be a short-term solution, however, if the flashing material is not compatible with the timber shingles

  • where rust has corroded right through the metal, is close to doing that, or a long-term solution is required, then the flashing should be replaced. The replacement flashing material must be compatible with both the timber shingles and the guttering/downpipes. The acids contained in cedar and the copper in copper-based preservative treatments will attack many metals. Copper will not be affected, but galvanised steel and aluminium should be post-form coated. In some cases, suitable prefinished flashings may be available. Butyl rubber can also be used as a flashing material

  • flashings are a key part of the weatherproofing of a roof. Poorly installed flashings can lead to leaks, so replacement of flashings should be carried out by a person with the appropriate skills, experience and equipment. This is not work for a novice. Work on roofs is restricted building work under the Building Act and anyone engaged to carry out this work must be a licensed building practitioner or be supervised by an LBP

  • where the shingles are in good condition, homeowners can clean the roof and flashings annually with low-pressure washing, the water stream directed down the roof. Never use high-pressure waterblasting or wire-bristled brushes or brooms

  • older shakes and shingle roofs can become brittle and can be damaged when someone carelessly walks on the roof. Great care is needed with any repairs or maintenance. Hiring a well-experienced contractor with the appropriate equipment to avoid damage may be a good solution

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Cause

Air-borne salt, dust or dirt accumulating on or under the flashing

Repair

  • As for the first repair

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