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How to Maintain and Repair a Metal Roof

If your home has a metal roof, it should last 40, 50 years or longer with regular maintenance. Taking care of problems early will help ensure you get the maximum possible service life!

Repair processes vary widely depending on the type of metal roof. Whenever repairing a metal roof, be sure to use compatible materials.

Many metals react, causing corrosion. Some woods and other chemicals can also cause corrosion. Be sure to read your manufacturer’s metal roof care instructions.

While the required maintenance steps vary, we’ve assembled tips on how to maintain and repair most types of metal roofs used in residential construction. Read on to learn more on how to maintain and repair most types of metal roofs

General Repairs

  1. Pull and re-nail loose nails.
  2. Look for holes, rust patches and other signs of damage.
  3. Seal leaks with urethane roof cement. Urethane protects against UV breakdown better than asphalt or plastic roof cement.
  4. Re-calk edges and seams along flashing using urethane roof cement.

Patching a Hole

  1. It is important to use the same type of metal as the roof, otherwise your patch can cause corrosion. First, clean the area with an all-purpose cleaner and a wire brush and let it dry completely.
  2. Your patch should be at least 2 inches larger than the damaged area, and remove the corners with tin snips. Fold the edges under ½ inch. Sand the folded part until its shiny. Put flux on the roof where the patch will be, and on the edges of the patch. Place the patch on the hole and weight it down with a brick. Hold solder on the seam and heat with soldering iron so that it melts and runs under the patch. Do this all the way around the patch, not leaving any open spaces.
  3. Cut two more patches larger than the hole. Coat the area on the roof with cement. Press one patch and apply another coat of cement. Repeat with the last patch and apply one last coat of roofing cement.

Long Run Metal Roofs

There are two basic types of long run metal roofs: fixed-through and clip-on. Clip-on roofing can be used on flatter roofs, with slopes as little as one degree. The clips go into the roofing first, which is then fixed to the roof purlins. Fixed-through corrugated sheeting is used on more sloping roofs (not below eight degrees). Sheets are held onto the roof with fastenings drilled through the roofing material.

Any repairs that penetrate the metal of a long run roof could invalidate your warranty. Check with the roofing manufacturer before doing any repairs. Also, check with the manufacturer before cleaning or attaching fastenings. You will need to know the correct cleaners and metals to use to prevent damage. For example, if your roof is made of zinc/aluminum-coated steel, you need to use soft zinc or aluminum flashings. Lead, even just from marking with a lead pencil, could cause reactions and corrosion.

Steel Roofs

Lifted Flashing – Flashing protects vulnerable spots, and if they are damaged you may have leaking. Lead or aluminum flashing that has bent or pulled away can be reshaped to the roof profile, but you might want to consider replacing them with a heavier grade flashing.

Loose Nails and Screws – Nails and screws that hold flashing into place need to be replaced if they fail. Consider replacing them with spiral shank nails or screws for better hold.

Dented and Damaged Sheets – If you can access the underside of the roof, you can push out smaller dents. Badly damaged sheets will need to be replaced.

Buckling and Tearing – Buckling and tearing can be caused by heat or by too few joints. Badly done repairs can also cause buckles. Remove and replace sheets with shorter lengths and more joints.

Corrosion – Metal will corrode due to grime, steel debris left on the roof, or contact with incompatible metals or woods (such as cedar, which is highly acidic). First, remove the cause. Then, clean the roof by sanding all the rust away. Apply a zinc-rich primer to sanded areas, then prime entire roof with galvanized iron primer and top coats. Severely corroded roofing will need to be replaced.

Bi-Metallic Corrosion – Many metals when put together will cause corrosion, especially when they become wet. Check with the roof manufacturer to find out what metals are compatible with your roof. If your roof is zinc/aluminum coated steel, it is not compatible with copper, pre-painted steel, galvanized steel, or lead. Make sure copper pipes don’t direct water onto metal roofing or gutters. Flashing should be made from the same material as your roof.

Corrosion at Roof Ridges – Salt, dust, or sand catching under the roof ridges can cause corrosion. If this happens, remove the ridging and clean the deposits. Remove the rust. Prime the area and replace the ridging. Replace any badly corroded ridging or roof panels.

Pre-Painted Steel Roofs – Factory coated steel is rust resistant and should need little repair for the first 15 years after installation.

Peeling Paint and Chalking – Weather can cause peeling paint and chalking (white powdery buildup). If the warranty period for the roof has expired, remove loose paint and repaint according to the manufacturers instructions.

Minor Scratches – Minor scratches (most don’t affect weather tightness) are best left alone, since patching with paint will show up more than the scratch. If sheets are badly damaged they will need to be replaced.

Surface Stains – Surface Stains can form from poor pre-paint preparation or with runoff from lead flashing. Lift the flashing, prime and paint both sides with acrylic topcoat to match the roof.

Unpainted Metal Roofs

White Rust – When water droplets sit on the surface of an unpainted metal roof, white rust can form. Scrub them off with a plastic brush, not wire. Regular cleaning will prevent these, or you can paint the steel to reduce corrosion.

Red Rust – This is most common on zinc/aluminum or galvanized steel. The only long-term solution is to find and remove the cause. Possible causes are: run off from cedar, redwood, CCA timbers (those treated with copper, chrome, and arsenic), glass, or painted steel; run off from clear or opaque sheeting; a corrosive environment (for example, a nearby swimming pool); or use of lead flashings or stainless steel fixings with zinc/aluminum alloy steel. Once you have identified and eliminated the cause, you can remove the rust, prime the area with a coating that is recommended by the manufacturer.

Corrosion – Corrosion can be caused by debris collecting under flashings and roofing overlaps, and can be avoided through regular maintenance, carefully cleaning under flashings and overlaps.
The underside of galvanized steel sheets can corrode if they are not primed or washed. Usually by the time you notice this, the damage is severe and the sheets will need to be replaced. Priming overlapping sheets can prevent this.

- Local Fresh  updated June 16th, 2008
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